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AutonomicPEM-relevant

Autonomic Nervous System

340 studies in the atlas

Autonomic dysfunction is among the most consistently reported abnormalities in ME/CFS. Studies document heart rate variability impairments, orthostatic intolerance, postural orthostatic tachycardia syndrome (POTS), and abnormal blood pressure regulation across patient populations. These findings reflect dysregulation of the autonomic nervous system — the network governing heart rate, blood pressure, and circulatory response to positional change. Research explores links between autonomic dysfunction, endothelial dysfunction, vascular tone, and impaired cerebral blood flow, suggesting a systemic vascular component to ME/CFS pathophysiology.

What we know

  • Orthostatic intolerance is reported by a majority of ME/CFS patients and can be demonstrated with tilt table testing
  • POTS has been documented in ME/CFS cohorts, particularly among younger patients
  • Reduced cerebral blood flow during upright posture has been observed in multiple studies
  • Altered heart rate variability has been reported, suggesting sympathetic-parasympathetic imbalance

What remains uncertain

  • Small fiber neuropathy, found in a subset of patients, may contribute to autonomic symptoms
  • Autoantibodies against adrenergic receptors have been reported in small studies and could play a role, though replication is needed
  • Blood volume reduction may contribute to orthostatic intolerance in some patients
  • The relationship between autonomic dysfunction and PEM is likely bidirectional, but the mechanisms are not well mapped

What is emerging

  • Whether autonomic dysfunction in ME/CFS is a primary driver of symptoms or a secondary consequence of other processes
  • Which assessment protocols are most appropriate for this patient population
  • Whether specific autonomic subtypes predict treatment response
  • Whether interventions such as vagus nerve stimulation or autonomic retraining have measurable benefit in ME/CFS specifically

Start here

E0 ConsensusPEM unclearPreliminary

Systematic literature review: treatment of postural orthostatic tachycardia syndrome (POTS).

Schiweck, Nicole, Langer, Katharina, Maier, Andrea et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2026

This review examined treatments for POTS (postural orthostatic tachycardia syndrome), a condition where your heart rate jumps significantly when you stand up, causing dizziness and fatigue. POTS is common in people with ME/CFS. The researchers looked at 45 studies and found that simple first-line treatments like compression socks, physical training, extra salt, and a vagus nerve stimulation device may help, while certain medications like ivabradine and beta-blockers also showed promise in some studies.

Research Momentum

340 publications over 34 years. Recent trend: steady (19/year over the last 3 years).

All Studies

340 studies, sorted by review status and evidence level

E0 ConsensusPEM unclearModerate confidenceEditor reviewed

Mapping cerebral blood flow in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and orthostatic intolerance: insights from a systematic review.

Christopoulos, Elena M, Tantanis, Darcy, Huang, Katherine et al.·Journal of translational medicine·2025

This review examined 118 research studies to understand how blood flow to the brain changes in ME/CFS patients, particularly those who also experience orthostatic intolerance (difficulty maintaining blood pressure when standing). Researchers found that blood flow to the brain is often reduced in both conditions, and when patients have both ME/CFS and orthostatic intolerance together, the reduction in brain blood flow appears to be even more pronounced. This finding suggests that measuring brain blood flow might help doctors track how severe the disease is.

Autonomic Nervous System
E0 ConsensusPEM unclearModerate confidenceMeta-AnalysisEditor reviewed

Objective sleep measures in chronic fatigue syndrome patients: A systematic review and meta-analysis.

Mohamed, Abdalla Z, Andersen, Thu, Radovic, Sanja et al.·Sleep medicine reviews·2023

This study looked at 24 research papers that measured sleep objectively (using devices and tests, not just patient reports) in people with ME/CFS. The researchers found that ME/CFS patients do indeed have real, measurable sleep problems—they take longer to fall asleep, wake up more during the night, and don't get good-quality sleep. Interestingly, these sleep problems looked slightly different in teenagers compared to adults with ME/CFS.

SleepAutonomic Nervous System
E0 ConsensusPEM unclearModerate confidenceSystematic-ReviewEditor reviewed

A systematic review of neurological impairments in myalgic encephalomyelitis/ chronic fatigue syndrome using neuroimaging techniques.

Maksoud, Rebekah, du Preez, Stanley, Eaton-Fitch, Natalie et al.·PloS one·2020

This review examined 55 studies that used brain imaging techniques to look for physical differences in the brains of people with ME/CFS compared to healthy people. The researchers found evidence that ME/CFS affects how the nervous system works, including changes in brain structure and blood flow. However, the findings weren't consistent across all studies, meaning scientists still don't have a complete picture of what's happening in the brain.

Autonomic Nervous SystemCognitive Impairment
E0 ConsensusPEM unclearModerate confidenceMeta-AnalysisEditor reviewed

Evidence of altered cardiac autonomic regulation in myalgic encephalomyelitis/chronic fatigue syndrome: A systematic review and meta-analysis.

Nelson, Maximillian J, Bahl, Jasvir S, Buckley, Jonathan D et al.·Medicine·2019

This study looked at how the hearts of people with ME/CFS respond differently compared to healthy people, focusing on heart rate and its patterns. Researchers reviewed 64 previous studies and found that ME/CFS patients tend to have higher resting heart rates, unusual heart rate responses to position changes, and different patterns in heart rate variability (the natural variation in time between heartbeats). These findings suggest that the nervous system that controls heart function may work differently in people with ME/CFS.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Cognitive Dysfunction in Chronic Fatigue Syndrome: a Review of Recent Evidence.

Cvejic, Erin, Birch, Rachael C, Vollmer-Conna, Uté·Current rheumatology reports·2016

People with ME/CFS commonly experience 'brain fog'—problems with memory, attention, and concentration. While these cognitive problems are real and significantly impact daily life, the exact biological causes remain unclear. This review suggests that problems with blood flow to the brain and nervous system dysfunction may be involved, and calls for standardized testing methods to better understand what's happening.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceSystematic-ReviewEditor reviewed

Malfunctioning of the autonomic nervous system in patients with chronic fatigue syndrome: a systematic literature review.

Van Cauwenbergh, Deborah, Nijs, Jo, Kos, Daphne et al.·European journal of clinical investigation·2014

This review examined 27 studies that looked at how the autonomic nervous system (the part of your nervous system that controls automatic body functions like heart rate) works differently in ME/CFS patients compared to healthy people. Researchers found that ME/CFS patients often show unusual heart rate responses during tilting tests, which is consistent with a condition called postural orthostatic tachycardia syndrome (POTS). These autonomic nervous system differences might help doctors diagnose ME/CFS.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Dysautonomias: clinical disorders of the autonomic nervous system.

Goldstein, David S, Robertson, David, Esler, Murray et al.·Annals of internal medicine·2002

This review examines dysautonomias—conditions where the autonomic nervous system (the part of your body that controls heart rate, blood pressure, and other automatic functions) stops working properly. The authors discuss how these problems can range from occasional fainting spells to serious nerve damage. Importantly, they note that ME/CFS patients often show signs of orthostatic intolerance (difficulty maintaining blood pressure when standing), but a common treatment that works for other autonomic conditions does not appear to help ME/CFS patients.

Autonomic Nervous System
E0 ConsensusPEM not requiredPreliminaryEditorialEditor reviewed

Chronic fatigue syndrome: what role does the autonomic nervous system play in the pathophysiology of this complex illness?

Gerrity, Timothy R, Bates, Janet, Bell, David S et al.·Neuroimmunomodulation·2002

This paper brings together expert opinions about how the autonomic nervous system (the part of your nervous system that controls automatic functions like heart rate and breathing) may be involved in ME/CFS. The authors reviewed what was known in 2000 about connections between autonomic nervous system problems and other system dysfunctions seen in ME/CFS, including immune and hormone abnormalities.

Autonomic Nervous System
E0 ConsensusPEM unclearPreliminarySystematic-ReviewEditor reviewed

Systematic literature review: treatment of postural orthostatic tachycardia syndrome (POTS).

Schiweck, Nicole, Langer, Katharina, Maier, Andrea et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2026

This review examined treatments for POTS (postural orthostatic tachycardia syndrome), a condition where your heart rate jumps significantly when you stand up, causing dizziness and fatigue. POTS is common in people with ME/CFS. The researchers looked at 45 studies and found that simple first-line treatments like compression socks, physical training, extra salt, and a vagus nerve stimulation device may help, while certain medications like ivabradine and beta-blockers also showed promise in some studies.

Autonomic Nervous System
E0 ConsensusPEM unclearModerate confidenceSystematic-ReviewEditor reviewed

Systematic review: digital biomarkers of fatigue in chronic diseases.

Aboagye, Nana Yaw, Hinchliffe, Chloe, Del Din, Silvia et al.·NPJ digital medicine·2025

This review looked at studies using wearable devices (like fitness trackers) to measure fatigue in people with various chronic illnesses, including ME/CFS. Researchers found that across many diseases, reduced physical activity, more sitting time, and problems with the body's automatic nervous system (which controls heart rate and breathing) were linked to higher fatigue levels. The findings suggest that wearable devices might help doctors personalize fatigue management for individual patients.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Autoimmune Autonomic Neuropathy: From Pathogenesis to Diagnosis.

Nakane, Shunya, Koike, Haruki, Hayashi, Tomohiro et al.·International journal of molecular sciences·2024

This review describes autoimmune autonomic ganglionopathy (AAG), a rare condition where the immune system attacks nerve cells that control automatic body functions like heart rate and blood pressure. The authors explain how doctors can diagnose AAG and how it differs from other similar conditions, including ME/CFS and long COVID, which can have overlapping symptoms.

Autonomic Nervous SystemDiagnostics
E0 ConsensusPEM unclearModerate confidenceEditorialEditor reviewed

Understanding, diagnosing, and treating Myalgic encephalomyelitis/chronic fatigue syndrome - State of the art: Report of the 2nd international meeting at the Charité Fatigue Center.

Steiner, Sophie, Fehrer, Annick, Hoheisel, Friederike et al.·Autoimmunity reviews·2023

Over 100 international researchers gathered in Berlin in May 2023 to discuss what we currently know about ME/CFS, how to diagnose it, and how to treat it. The conference highlighted that ME/CFS involves problems with the immune system, blood vessel function, and nervous system control, and that some cases may be triggered by viruses reactivating in the body. Despite growing interest due to Long COVID, ME/CFS remains under-researched and needs significantly more funding to find better diagnostic tests and targeted treatments.

Autonomic Nervous SystemImmune System
E0 ConsensusPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Autoimmune autonomic nervous system imbalance and conditions: Chronic fatigue syndrome, fibromyalgia, silicone breast implants, COVID and post-COVID syndrome, sick building syndrome, post-orthostatic tachycardia syndrome, autoimmune diseases and autoimmune/inflammatory syndrome induced by adjuvants.

Malkova, A M, Shoenfeld, Y·Autoimmunity reviews·2023

This review examined whether ME/CFS, fibromyalgia, and several other conditions share a common problem: the immune system mistakenly attacks nerve controls that regulate heart rate, blood pressure, and other automatic body functions. Researchers found that people with these conditions often have similar symptoms like fatigue, dizziness, and brain fog, and some have autoantibodies (immune proteins) that target nerve receptors. The authors propose this 'autonomic nervous system imbalance' could be a unifying mechanism explaining why these diverse conditions feel so similar.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceMeta-AnalysisEditor reviewed

Reduced Heart Rate Variability in Patients With Medically Unexplained Physical Symptoms: A Meta-Analysis of HF-HRV and RMSSD.

Vreijling, Sarah R, Troudart, Yael, Brosschot, Jos F·Psychosomatic medicine·2021

This study looked at heart rate variability (how much your heart rate changes moment-to-moment) in people with chronic fatigue syndrome, irritable bowel syndrome, and fibromyalgia. Researchers combined results from 58 previous studies and found that patients with these conditions had lower heart rate variability than healthy people, suggesting their nervous systems may not be regulating heart rate as flexibly as they should.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceSystematic-ReviewEditor reviewed

Sympathetic nervous system dysfunction in fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, and interstitial cystitis: a review of case-control studies.

Martínez-Martínez, Laura-Aline, Mora, Tania, Vargas, Angélica et al.·Journal of clinical rheumatology : practical reports on rheumatic & musculoskeletal diseases·2014

This review examined whether ME/CFS, fibromyalgia, IBS, and interstitial cystitis share a common problem: an overactive stress-response system in the nervous system. Researchers looked at 196 published studies that compared patients with these conditions to healthy controls. They found that about 65% of studies showed these patients have a nervous system stuck in 'overdrive,' which could explain why these conditions often occur together.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceSystematic-ReviewEditor reviewed

Heart rate variability in patients with fibromyalgia and patients with chronic fatigue syndrome: a systematic review.

Meeus, Mira, Goubert, Dorien, De Backer, Fien et al.·Seminars in arthritis and rheumatism·2013

This review looked at 16 studies comparing heart rhythm patterns between people with fibromyalgia, chronic fatigue syndrome, and healthy controls. Both conditions showed changes in how the heart responds to stress, but the patterns were different: fibromyalgia patients had heart rhythm problems throughout the day, while CFS patients mainly showed them during sleep. Exercise helped improve heart rhythm patterns in fibromyalgia patients.

Autonomic Nervous System
E0 ConsensusPEM not requiredPreliminaryReview-NarrativeEditor reviewed

[Etiology of functional somatic syndromes].

Nakao, Mutsuhiro·Nihon rinsho. Japanese journal of clinical medicine·2009

This review explores why people develop functional somatic syndromes—a group of conditions including ME/CFS, fibromyalgia, and irritable bowel syndrome that cause real suffering but don't show clear structural damage on standard tests. The authors suggest that mood, stress sensitivity, genetics, and environment all play important roles in these conditions, and that how patients interact with their doctors matters too.

Autonomic Nervous System
E0 ConsensusPEM not requiredWeak / uncertainMeta-AnalysisEditor reviewed

As good as it gets? A meta-analysis and systematic review of methodological quality of heart rate variability studies in functional somatic disorders.

Tak, Lineke M, Riese, Harriëtte, de Bock, Geertruida H et al.·Biological psychology·2009

This research review looked at whether people with ME/CFS and similar conditions have problems with their nervous system's ability to regulate heart rate. Researchers combined results from 23 studies involving 533 patients and found weak evidence that patients may have lower parasympathetic nerve activity (the calming part of the nervous system) compared to healthy people. However, the evidence was not strong enough to draw firm conclusions, and the studies reviewed had many quality problems that made the results unreliable.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceEditorialEditor reviewed

Central nervous system abnormalities in fibromyalgia and chronic fatigue syndrome: new concepts in treatment.

Gur, Ali, Oktayoglu, Pelin·Current pharmaceutical design·2008

This review examines how ME/CFS and fibromyalgia may both involve problems in the nervous system—specifically in how the brain processes pain, manages stress hormones, and controls automatic body functions. The authors discuss why current treatments are limited and explore new medication approaches that target brain chemicals involved in pain and fatigue.

SleepAutonomic Nervous SystemCognitive Impairment
E0 ConsensusPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Autonomic nervous system derangement in fibromyalgia syndrome and related disorders.

Cohen, H, Neumann, L, Kotler, M et al.·The Israel Medical Association journal : IMAJ·2001

This review examines how the autonomic nervous system—the part of your nervous system that controls heart rate, breathing, and digestion automatically—may not work properly in fibromyalgia and related conditions like ME/CFS and irritable bowel syndrome. Researchers found evidence that this system dysfunction could have important health consequences, including increased risk of heart problems. However, studies on this topic have produced mixed and sometimes contradictory results.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Controlled exposures to volatile organic compounds in sensitive groups.

Fiedler, N, Kipen, H M·Annals of the New York Academy of Sciences·2001

This review looked at studies where people with chemical sensitivities were exposed to different odors and chemical mixtures in controlled lab settings. Researchers found that people with chemical sensitivities did have real symptoms when exposed to certain chemicals, even at low levels, but these symptoms weren't always linked to measurable changes in heart rate, breathing, or other body functions that usually indicate stress.

Autonomic Nervous System
E0 ConsensusPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Chronic pain and fatigue syndromes: overlapping clinical and neuroendocrine features and potential pathogenic mechanisms.

Clauw, D J, Chrousos, G P·Neuroimmunomodulation·1997

This review examines fibromyalgia and chronic fatigue syndrome, two conditions with overlapping symptoms of pain and exhaustion that have been described throughout medical history under different names. The authors propose that both conditions stem from problems in the central nervous system—the brain and spinal cord—particularly in areas that control hormone levels, pain sensing, and automatic body functions. They suggest that immune system changes seen in these conditions are side effects rather than root causes.

Autonomic Nervous SystemImmune System
E0 ConsensusPEM unclearModerate confidenceSystematic-ReviewEditor reviewed

Decreased Heart Rate Variability Is Associated with Increased Fatigue Across Different Medical Populations: A Systematic Review.

Penfold, Sophie Maria, Cunningham, James, Whelan, Pauline et al.·Pathophysiology : the official journal of the International Society for Pathophysiology·2025

This review looked at 17 studies examining the link between fatigue and heart rate variability (HRV)—a measure of how well your nervous system is working. The researchers found that people who feel more fatigued tend to have imbalanced heart rate patterns, suggesting their autonomic nervous system (the part controlling automatic body functions) may not be working properly. ME/CFS patients were the most studied group, making this particularly relevant to understanding fatigue in this condition.

Autonomic Nervous System
E0 ConsensusPEM not requiredHigher confidenceMeta-AnalysisEditor reviewed

Heart rate variability in patients with somatic symptom disorders and functional somatic syndromes: A systematic review and meta-analysis.

Ying-Chih, Cheng, Yu-Chen, Huang, Wei-Lieh, Huang·Neuroscience and biobehavioral reviews·2020

This large review combined results from 85 studies comparing heart rhythm patterns between people with conditions like fibromyalgia and ME/CFS (functional somatic syndromes) and healthy people. Researchers found that patients with these conditions have lower heart rate variability—meaning their heart's rhythm is less flexible and adaptive—which suggests their nervous system may not be responding normally to stress and daily activities.

Autonomic Nervous System
E1 ReplicatedPEM not requiredPreliminaryRCTEditor reviewed

Effects of acupuncture and moxibustion on heart rate variability in chronic fatigue syndrome patients: Regulating the autonomic nervous system in a clinical randomized controlled trial.

Li, Tong, Litscher, Gerhard, Zhou, Yudian et al.·Complementary therapies in medicine·2025

This study tested whether acupuncture and moxibustion (a traditional heat therapy) could help people with chronic fatigue syndrome by measuring changes in heart rate variability, which reflects how well the nervous system is working. Researchers divided 175 CFS patients into groups receiving different acupuncture treatments, fake acupuncture, or moxibustion over 10 sessions. Both acupuncture and moxibustion reduced fatigue symptoms, with combining both approaches working best, and the treatments appeared to help balance the body's stress response system.

Autonomic Nervous System
E1 ReplicatedPEM requiredModerate confidenceRCTEditor reviewed

Assessing fatigue in myalgic encephalomyelitis/chronic fatigue syndrome patients before and after treatment with bright light therapy: A prospective randomized controlled crossover study.

Ludwig, Birgit, Hauer, Lea, Böck, Marion et al.·Sleep medicine·2025

Researchers tested whether bright light therapy—using special light boxes at home for two weeks—could help reduce fatigue in ME/CFS patients. While fatigue scores did improve immediately after the light therapy, these improvements did not remain significant when compared fairly to a waitlist control group. The study did find that bright light therapy may have helped patients concentrate better and react faster to tasks.

Autonomic Nervous SystemCognitive Impairment
E1 ReplicatedPEM unclearModerate confidenceRCTEditor reviewed

Compression Stockings Improve Cardiac Output and Cerebral Blood Flow during Tilt Testing in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) Patients: A Randomized Crossover Trial.

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Medicina (Kaunas, Lithuania)·2021

Many ME/CFS patients experience dizziness and other symptoms when standing up (called orthostatic intolerance). This study tested whether compression stockings—tight socks that squeeze the legs—could help. Researchers found that when ME/CFS patients wore compression stockings during a standing test, their heart pumped blood more effectively and their brain received better blood flow compared to when they wore regular socks.

Autonomic Nervous System
E1 ReplicatedPEM requiredModerate confidenceObservationalEditor reviewed

Cerebral blood flow is reduced in ME/CFS during head-up tilt testing even in the absence of hypotension or tachycardia

C. M. C. van Campen, F. C. Visser, P. C. Rowe·Journal of Internal Medicine·2020·n=429

In the largest study of its kind, 429 ME/CFS patients underwent head-up tilt testing with simultaneous cerebral blood flow monitoring. Nearly all ME/CFS patients showed significantly reduced cerebral blood flow when upright, even when blood pressure and heart rate were normal. The reduction correlated with symptom severity.

Autonomic Nervous SystemCognitive Impairment
E1 ReplicatedPEM not requiredPreliminaryRCTEditor reviewed

Acupuncture and Moxibustion have Different Effects on Fatigue by Regulating the Autonomic Nervous System: A Pilot Controlled Clinical Trial.

Shu, Qing, Wang, Hua, Litscher, Daniela et al.·Scientific reports·2016

This study tested whether two traditional Chinese medicine treatments—acupuncture and moxibustion (warming therapy)—could help reduce fatigue in ME/CFS patients. Forty-five people were divided into three groups: two received acupuncture and one received moxibustion. Both treatments reduced fatigue, but moxibustion appeared to work better, especially over the long term, possibly by calming the nervous system.

Autonomic Nervous System
E1 ReplicatedPEM not requiredModerate confidenceRCTEditor reviewed

Ubiquinol-10 supplementation improves autonomic nervous function and cognitive function in chronic fatigue syndrome.

Fukuda, Sanae, Nojima, Junzo, Kajimoto, Osami et al.·BioFactors (Oxford, England)·2016

This study tested whether taking a supplement called ubiquinol-10 (a form of coenzyme Q10) could help people with ME/CFS feel better. Researchers first gave 20 patients ubiquinol-10 for 8 weeks and saw improvements, then tested it more rigorously in 43 patients who either received ubiquinol-10 or a placebo for 12 weeks. The results suggested that ubiquinol-10 may help improve some CFS symptoms, particularly problems with nerve function and thinking ability.

Autonomic Nervous System
E1 ReplicatedPEM not requiredModerate confidenceRCTEditor reviewed

Effects of low-dose clonidine on cardiovascular and autonomic variables in adolescents with chronic fatigue: a randomized controlled trial.

Fagermoen, Even, Sulheim, Dag, Winger, Anette et al.·BMC pediatrics·2015

This study tested whether a low-dose blood pressure medication called clonidine could help adolescents with ME/CFS, particularly those experiencing dizziness when standing up. Researchers found that clonidine did reduce certain stress hormones in the blood and improved some measurements of heart rhythm control while lying down, but it did not relieve the actual symptoms of dizziness or improve heart function during positional changes.

Autonomic Nervous System
E1 ReplicatedPEM not requiredPreliminaryRCTEditor reviewed

Home orthostatic training in chronic fatigue syndrome--a randomized, placebo-controlled feasibility study.

Sutcliffe, K, Gray, J, Tan, M P et al.·European journal of clinical investigation·2010

Some ME/CFS patients experience sudden drops in blood pressure when standing up, which may worsen fatigue. This study tested whether daily tilting exercises done at home could help stabilize blood pressure and improve symptoms. Over 6 months, patients who did the tilting exercises showed slightly better blood pressure control compared to those doing fake exercises, though fatigue improvements were modest.

Autonomic Nervous System
E1 ReplicatedPEM not requiredHigher confidenceRCTEditor reviewed

Combination therapy with hydrocortisone and fludrocortisone does not improve symptoms in chronic fatigue syndrome: a randomized, placebo-controlled, double-blind, crossover study.

Blockmans, Daniel, Persoons, Philippe, Van Houdenhove, Boudewijn et al.·The American journal of medicine·2003

Researchers tested whether a combination of two medications (hydrocortisone and fludrocortisone) could reduce fatigue and improve well-being in ME/CFS patients. Over 6 months, 80 patients took either the medication combination or placebo in a blinded study where neither patients nor doctors knew which they were receiving. The medications did not help—patients reported the same level of fatigue and well-being whether they were taking the drugs or placebo.

Autonomic Nervous System
E1 ReplicatedPEM not requiredModerate confidenceRCTEditor reviewed

Fludrocortisone acetate to treat neurally mediated hypotension in chronic fatigue syndrome: a randomized controlled trial.

Rowe, P C, Calkins, H, DeBusk, K et al.·JAMA·2001

Many people with ME/CFS experience a drop in blood pressure when standing up (called neurally mediated hypotension), which may contribute to symptoms like dizziness and fatigue. This study tested whether a medication called fludrocortisone could help reduce ME/CFS symptoms in 100 patients with this blood pressure problem. After 9 weeks of treatment, the medication did not work better than placebo, suggesting it may not be an effective standalone treatment for this group.

Autonomic Nervous System
E1 ReplicatedPEM not requiredPreliminaryRCTEditor reviewed

A preliminary placebo-controlled crossover trial of fludrocortisone for chronic fatigue syndrome.

Peterson, P K, Pheley, A, Schroeppel, J et al.·Archives of internal medicine·1998

This study tested whether a low-dose steroid medication called fludrocortisone could help ME/CFS patients feel better. Twenty participants took either the medication or a placebo for 6 weeks each, in random order. The medication did not improve fatigue, other symptoms, or physical function compared to placebo, and it did not cause more side effects than placebo.

Autonomic Nervous System
E1 ReplicatedPEM unclearPreliminaryRCTEditor reviewed

The Use of Heart Rate Variability-Biofeedback (HRV-BF) as an Adjunctive Intervention in Chronic Fatigue Syndrome (CSF/ME) in Long COVID: Results of a Phase II Controlled Feasibility Trial.

Cossu, Giulia, Kalcev, Goce, Primavera, Diego et al.·Journal of clinical medicine·2025

This study tested whether a technique called heart rate variability biofeedback (HRV-BF)—which uses breathing exercises and computer feedback to help regulate your nervous system—could help people with Long COVID who have severe fatigue. Participants received 10 sessions over 5 weeks, and the results showed that people in the treatment group experienced greater improvement in severe fatigue compared to those receiving usual care. The treatment was well-tolerated with very few people dropping out, suggesting it could be a helpful add-on therapy for ME/CFS.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Understanding concussion in myalgic encephalomyelitis/chronic fatigue syndrome: Findings from the 2023 National Health Interview study.

Sirotiak, Zoe, Adamowicz, Jenna L, Thomas, Emily B K·Brain injury·2026

This study found that people with ME/CFS are nearly 5 times more likely to have had a concussion in the past year compared to people without ME/CFS. People with ME/CFS also experienced more falls and dizziness or balance problems. The researchers suggest that doctors should screen patients with ME/CFS more carefully for concussions and take steps to reduce their concussion risk.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryCross-SectionalEditor reviewed

Provocation of brachial plexus and systemic symptoms during the elevated arm stress test in individuals with myalgic encephalomyelitis/chronic fatigue syndrome or idiopathic chronic fatigue.

Edwards, Charles C, Byrnes, Julia M, Broussard, Camille A et al.·Journal of translational medicine·2025

Researchers tested whether a simple arm position exercise (holding arms overhead and opening/closing fists) could trigger symptoms in ME/CFS patients who struggle with overhead activities. They found that nearly all patients (97%) developed arm symptoms like pain, numbness, or heaviness during the test, and 41% also experienced whole-body symptoms like dizziness, brain fog, or a racing heart. This suggests that some ME/CFS patients may have nerve compression issues in their shoulders or neck that worsen with certain arm positions.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCase-ControlEditor reviewed

Diagnosis of chronic fatigue syndrome using beat-to-beat autonomic measurements.

Kujawski, Sławomir, Tabisz, Hanna, Morten, Karl J et al.·Journal of translational medicine·2025

Researchers used artificial intelligence to analyze how the heart and nervous system behave differently in ME/CFS patients compared to healthy people. By measuring heart rate changes beat-by-beat, they found a pattern that could identify ME/CFS patients with 89% accuracy. The key differences included a less responsive vagal nerve (which normally calms the body), a more active stress response in blood vessels, and less efficient heart pumping.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Awareness and Perception of Myalgic Encephalomyelitis and Chronic Fatigue Syndrome Among Pain Specialists: A Questionnaire-Based Study.

Uygun, Gürsan Güneş, Gözükızıl, Salim Taner, Bilen, Ayşegül·Cureus·2025

This study asked pain doctors in Turkey about their knowledge of ME/CFS and how they evaluate and treat patients with the condition. The results show that many pain specialists aren't familiar with ME/CFS, and some hold misconceptions—like thinking it's a type of depression or that intense exercise will help. This matters because pain doctors could potentially help ME/CFS patients, but they need better education about the condition first.

Autonomic Nervous System
E2 ModeratePEM requiredModerate confidenceObservationalEditor reviewed

Low Vasopressin in Myalgic Encephalomyelitise/Chronic Fatigue Syndrome.

Huhmar, Helena M, Soinne, Lauri S, Bertilson, Bo Christer et al.·Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists·2025

This study found that most people with ME/CFS have abnormally low levels of vasopressin, a hormone that helps your body control water balance and blood volume. The researchers measured this hormone and fluid markers in over 100 ME/CFS patients and discovered that 82% had vasopressin levels below the detectable range. This may help explain why many ME/CFS patients experience excessive thirst, frequent urination, and dizziness when standing up.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Autonomic Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): Findings from the Multi-Site Clinical Assessment of ME/CFS (MCAM) Study in the USA.

Issa, Anindita, Lin, Jin-Mann S, Chen, Yang et al.·Journal of clinical medicine·2025

This study found that people with ME/CFS experience much higher levels of autonomic nervous system problems—which control things like heart rate, blood pressure, and digestion—compared to healthy people. Nearly all ME/CFS patients (97%) had at least one autonomic symptom, with common complaints including dizziness, cold hands and feet, and difficulty standing up. The more autonomic symptoms someone had, especially in certain areas like blood pressure regulation and stomach problems, the more severe their overall illness tended to be.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceObservationalEditor reviewed

The Relation Between Cardiac Output and Cerebral Blood Flow in ME/CFS Patients with a POTS Response During a Tilt Test.

van Campen, C Linda M C, Visser, Frans C·Journal of clinical medicine·2025

When people with ME/CFS and POTS stand up, their blood pressure and heart rate don't respond normally, causing symptoms like dizziness and fatigue. This study looked at 260 ME/CFS patients during a tilt test to understand how the heart's output of blood relates to blood flow in the brain. The researchers found two different patterns: about two-thirds of patients showed their brain blood flow dropped at roughly the same rate as their heart's output decreased, while about one-third had a different pattern where their heart was racing but their heart output wasn't dropping as much, and their brain blood flow didn't follow the expected pattern.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Two Different Hemodynamic Responses in ME/CFS Patients with Postural Orthostatic Tachycardia Syndrome During Head-Up Tilt Testing.

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Journal of clinical medicine·2024

This study looked at how the bodies of ME/CFS patients with POTS (a condition causing rapid heart rate when standing) respond to positional changes differently than healthy people. Researchers found that ME/CFS patients with POTS fall into two groups: those with a smaller heart rate increase appear to have blood pooling in their legs, while those with a larger heart rate increase seem to have an overactive stress response system. These two different patterns might benefit from different treatments.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Plasma Neurofilament Light Chain: A Potential Biomarker for Neurological Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Azcue, Naiara, Tijero-Merino, Beatriz, Acera, Marian et al.·Biomedicines·2024

Researchers measured a protein called neurofilament light chain (NfL) in the blood of ME/CFS patients and healthy people. They found that ME/CFS patients had higher levels of this protein, which suggests nerve damage in the brain and nervous system. The patients with higher NfL levels also had more problems with memory, thinking clearly, and with their autonomic nervous system (the part that controls heart rate and other automatic body functions).

Autonomic Nervous SystemCognitive Impairment
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Do people with ME/CFS and joint hypermobility represent a disease subgroup? An analysis using registry data.

Mudie, Kathleen, Ramiller, Allison, Whittaker, Sadie et al.·Frontiers in neurology·2024

This study looked at whether ME/CFS patients with loose, flexible joints (joint hypermobility) form a distinct group with different symptoms and health impacts. Researchers surveyed 815 ME/CFS patients and found that about 16% had joint hypermobility. These patients reported worse quality of life, more pain, and more symptoms affecting their nervous system, thinking, digestion, and muscles compared to ME/CFS patients without joint hypermobility.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

The Cardiac Output-Cerebral Blood Flow Relationship Is Abnormal in Most Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients with a Normal Heart Rate and Blood Pressure Response During a Tilt Test.

van Campen, C Linda M C, Verheugt, Freek W A, Rowe, Peter C et al.·Healthcare (Basel, Switzerland)·2024

This study looked at how blood flow to the brain changes when ME/CFS patients stand up or tilt on a table. Researchers found that in 91% of patients, the heart wasn't pumping enough blood and the brain wasn't getting enough blood flow—and these two problems were directly connected. This suggests that blood vessels in the brain may not be working properly to compensate when blood flow drops, which could explain why many ME/CFS patients feel dizzy or faint when standing.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryMechanisticEditor reviewed

Phenylephrine alters phase synchronization between cerebral blood velocity and blood pressure in ME/CFS with orthostatic intolerance.

Medow, Marvin S, Stewart, Julian M·American journal of physiology. Regulatory, integrative and comparative physiology·2024

People with ME/CFS often experience brain fog and cognitive problems when standing up, possibly because their brain isn't getting enough blood flow and oxygen. This study tested whether a medication called phenylephrine could help restore brain blood flow and improve thinking during standing. The researchers found that phenylephrine was the only treatment tested that significantly improved both cognitive performance and the brain's ability to maintain stable blood flow during head-up tilting.

Autonomic Nervous SystemCognitive Impairment
E2 ModeratePEM not requiredPreliminaryLongitudinalEditor reviewed

Effects of whole-body cryotherapy and static stretching are maintained 4 weeks after treatment in most patients with chronic fatigue syndrome.

Kujawski, Sławomir, Zalewski, Paweł, Godlewska, Beata R et al.·Cryobiology·2023

This small study looked at whether a treatment combining cold therapy (whole-body cryotherapy) and stretching could help ME/CFS patients feel better for at least a month. Researchers found that 17 out of 22 patients reported improvements in fatigue, and brain function tests also improved. However, the study was small and had some dropouts, so the results should be viewed with caution.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryObservationalEditor reviewed

Repetitive transcranial magnetic stimulation ameliorates symptoms in patients with myalgic encephalomyelitis (chronic fatigue syndrome).

Miwa, Kunihisa, Inoue, Yukichi·IBRO neuroscience reports·2023

This small study tested a brain stimulation treatment called repetitive transcranial magnetic stimulation (rTMS) in 30 ME/CFS patients. The treatment targeted specific areas of the brain involved in movement and decision-making. After treatment, most patients reported improvements in their ability to do daily activities, reduced dizziness when standing, better balance, and less pain.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceEditor reviewed

Comparison of a 20 degree and 70 degree tilt test in adolescent myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) patients.

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Frontiers in pediatrics·2023

This study tested whether a gentler tilt test could detect blood flow problems in teenagers with ME/CFS, since the standard aggressive tilt test sometimes causes fainting in young patients. Researchers found that a mild 20-degree tilt reduced blood flow to the brain almost as much as the standard 70-degree tilt, but caused far fewer problems like fainting. This suggests doctors might be able to use a gentler test to diagnose blood flow issues in young ME/CFS patients.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceObservationalEditor reviewed

Skin Temperature Circadian Rhythms and Dysautonomia in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: The Role of Endothelin-1 in the Vascular Tone Dysregulation.

Cambras, Trinitat, Zerón-Rugerio, Maria Fernanda, Díez-Noguera, Antoni et al.·International journal of molecular sciences·2023

This study looked at how the bodies of people with ME/CFS respond to position changes and whether problems with their blood vessel function might be involved. Researchers compared 67 women with ME/CFS to 48 healthy women, measuring their blood pressure, heart rate, body temperature patterns, and blood markers related to blood vessel health. They found that people with ME/CFS had higher blood pressure and heart rate, disrupted daily temperature rhythms, and elevated levels of substances in the blood that suggest blood vessel problems.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryObservationalEditor reviewed

Autonomic Nervous System Regulation Effects of Epipharyngeal Abrasive Therapy for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Associated With Chronic Epipharyngitis.

Hirobumi, Ito·Cureus·2023

This study looked at how a throat treatment called epipharyngeal abrasive therapy (EAT) affects the nervous system in ME/CFS patients who also had chronic throat inflammation. Researchers measured heart rate and autonomic nervous system activity in 11 ME/CFS patients and 18 control patients during the procedure. They found that ME/CFS patients had higher resting heart rates and their nervous systems responded differently to the treatment compared to those without ME/CFS.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Orthostatic chronotropic incompetence in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

van Campen, C Linda M C, Verheugt, Freek W A, Rowe, Peter C et al.·IBRO neuroscience reports·2023

This study looked at how ME/CFS patients' hearts respond when they stand up or tilt upright during a medical test. Normally, when you stand, your heart rate increases to maintain blood flow to your brain. Researchers found that many ME/CFS patients had an incomplete heart rate increase despite their blood flow dropping significantly—a condition called chronotropic incompetence. This problem was more common in patients with more severe ME/CFS.

Autonomic Nervous System
E2 ModeratePEM requiredModerate confidenceObservationalEditor reviewed

Worsening Symptoms Is Associated with Larger Cerebral Blood Flow Abnormalities during Tilt-Testing in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS).

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Medicina (Kaunas, Lithuania)·2023

This study found that ME/CFS patients with worsening symptoms had larger problems with blood flow to their brain during a standing-up test (tilt test). When researchers compared patients at two visits, those who got sicker showed a bigger drop in brain blood flow (from 19% to 31%), while patients who stayed stable showed no change in blood flow reduction. The more severe a patient's ME/CFS became, the greater the reduction in blood flow to the brain.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryCross-SectionalEditor reviewed

Orthostatic Intolerance and Chronotropic Incompetence in Patients With Myalgic Encephalomyelitis or Chronic Fatigue Syndrome.

Miwa, Kunihisa·Circulation reports·2023

This study looked at how the hearts of ME/CFS patients respond when standing up. Researchers found that some patients have difficulty increasing their heart rate enough during standing, even when they don't experience the rapid heartbeat (POTS) that others with ME/CFS develop. For these patients, the ability to stand longer seemed to depend on having that rapid heartbeat response, suggesting their bodies may not be activating the right nervous system pathways to maintain blood pressure.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Influence of end-tidal CO2 on cerebral blood flow during orthostatic stress in controls and adults with myalgic encephalomyelitis/chronic fatigue syndrome.

van Campen, C Linda M C, Rowe, Peter C, Verheugt, Freek W A et al.·Physiological reports·2023

This study looked at how carbon dioxide (CO2) levels in the blood affect blood flow to the brain when people stand up or tilt on a table. Researchers compared 535 women with ME/CFS to 34 healthy women. They found that CO2 does affect brain blood flow in both groups similarly, but CO2 changes only partially explain why ME/CFS patients often have reduced blood flow to the brain during position changes.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCase-ControlEditor reviewed

Psychogenic Pseudosyncope: Real or Imaginary? Results from a Case-Control Study in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) Patients.

van Campen, C Linda M C, Visser, Frans C·Medicina (Kaunas, Lithuania)·2022

Some ME/CFS patients experience frequent fainting or near-fainting spells and have been told these are psychological in origin. This study compared brain blood flow in ME/CFS patients with these spells to ME/CFS patients without them during a tilt test (where you're gradually tilted upright). The group with fainting spells showed a much larger drop in blood flow to the brain, suggesting their symptoms have a physical cause rather than a psychiatric one.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Orthostatic intolerance and neurocognitive impairment in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS).

Gaglio, Caroline L, Islam, Mohammed F, Cotler, Joseph et al.·Epidemiologic methods·2022

This study looked at how often people with ME/CFS experience two symptoms that doctors use to diagnose the condition: difficulty thinking clearly (brain fog, memory problems) and dizziness when standing up. The researchers found that nearly all participants reported thinking and memory problems, while only a small number had standing-up dizziness without also having cognitive problems. This suggests these two symptoms overlap heavily in ME/CFS patients.

Autonomic Nervous SystemDiagnostics
E2 ModeratePEM not requiredPreliminaryObservationalEditor reviewed

Combination of whole body cryotherapy with static stretching exercises reduces fatigue and improves functioning of the autonomic nervous system in Chronic Fatigue Syndrome.

Kujawski, Sławomir, Słomko, Joanna, Godlewska, Beata R et al.·Journal of translational medicine·2022

This study tested whether combining cold therapy (whole body cryotherapy) with stretching exercises could help people with ME/CFS. Over 2 weeks, 32 people with ME/CFS and 18 healthy people did 10 sessions of stretching and cold exposure. People with ME/CFS experienced less fatigue and some improvements in thinking speed after the treatment, and the cold therapy was well-tolerated with no serious safety concerns.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceLongitudinalEditor reviewed

Physiological assessment of orthostatic intolerance in chronic fatigue syndrome.

Natelson, Benjamin H, Lin, Jin-Mann S, Blate, Michelle et al.·Journal of translational medicine·2022

This study tested how the bodies of ME/CFS patients respond when they shift from lying down to leaning upright for 10 minutes. Researchers measured heart rate, blood pressure, breathing, and carbon dioxide levels in the blood. They found that 60% of patients showed abnormal responses, with low blood carbon dioxide levels being the most common problem, followed by an excessively fast heartbeat when standing.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceLongitudinalEditor reviewed

Nonimprovement in Chronic Fatigue Syndrome: Relation to Activity Patterns, Uplifts and Hassles, and Autonomic Dysfunction.

Friedberg, Fred, Adamowicz, Jenna L, Bruckenthal, Patricia et al.·Psychosomatic medicine·2022

Researchers followed 148 people with ME/CFS for 6 months to understand why some patients improve while others don't. They tracked activity patterns, daily stressors and positive experiences, and measured heart rate variability (a sign of nervous system health). Patients who didn't improve had less heart rate variability and reported fewer positive daily experiences, but surprisingly, activity patterns like "push-crash" cycles didn't differ between improving and non-improving groups.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceObservationalEditor reviewed

Possible involvement of the autonomic nervous system in cervical muscles of patients with myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS).

Matsui, Takayoshi, Hara, Kazuhiro, Iwata, Makoto et al.·BMC musculoskeletal disorders·2021

This study looked at 1,226 hospitalized ME/CFS patients who received daily physical therapy focused on neck muscles. About 55% of patients recovered from ME/CFS after this treatment, and those who recovered showed changes in pupil size suggesting their nervous system function improved. The findings suggest that neck muscle problems and nervous system dysfunction may be connected in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM requiredPreliminaryCross-SectionalEditor reviewed

Post-Exertional Malaise May Be Related to Central Blood Pressure, Sympathetic Activity and Mental Fatigue in Chronic Fatigue Syndrome Patients.

Kujawski, Sławomir, Słomko, Joanna, Hodges, Lynette et al.·Journal of clinical medicine·2021

This study looked at 101 ME/CFS patients to understand post-exertional malaise (PEM)—the worsening of symptoms after activity that many patients experience. Researchers measured blood pressure, nervous system function, and fatigue levels in patients with and without PEM. They found that patients with PEM had higher mental fatigue, lower central blood pressure, and greater nervous system imbalance at rest, but the researchers caution that these findings need to be confirmed by larger studies.

Autonomic Nervous SystemPost-Exertional Malaise
E2 ModeratePEM not requiredPreliminaryLongitudinalEditor reviewed

Relationship between Cardiopulmonary, Mitochondrial and Autonomic Nervous System Function Improvement after an Individualised Activity Programme upon Chronic Fatigue Syndrome Patients.

Kujawski, Sławomir, Cossington, Jo, Słomko, Joanna et al.·Journal of clinical medicine·2021

This study tested whether a personalized activity program could help ME/CFS patients feel less tired and function better. Thirty-four patients followed a 16-week program tailored to their individual abilities. After the program, patients reported significant improvements in fatigue, and blood tests showed improvements in mitochondrial markers (Mfn1 and Mfn2)—the energy-producing components of cells. However, about half of the patients found exercise difficult to tolerate.

Autonomic Nervous SystemPost-Exertional Malaise
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Limbic Perfusion Is Reduced in Patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS).

Li, Xia, Julin, Per, Li, Tie-Qiang·Tomography (Ann Arbor, Mich.)·2021

Researchers used a specialized brain imaging technique to measure blood flow in the brains of ME/CFS patients and compared it to healthy people. They found that patients with ME/CFS have reduced blood flow in several areas of the limbic system—the part of the brain that helps control emotions, automatic body functions, and memory. The amount of reduced blood flow was also linked to how severe patients' symptoms were.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Comparison of the finger plethysmography derived stroke volumes by Nexfin CO Trek and suprasternal aortic Doppler derived stroke volume measurements in adults with myalgic encephalomyelitis/chronic fatigue syndrome and in healthy controls.

van Campen, C Linda M C, Verheugt, Freek W A, Rowe, Peter C et al.·Technology and health care : official journal of the European Society for Engineering and Medicine·2021

This study compared two different ways of measuring how much blood the heart pumps with each beat during a tilt table test (where patients lie down then are tilted upright). Researchers tested 154 ME/CFS patients and 39 healthy people using finger cuff measurements and ultrasound of the heart. They found that the finger cuff method gave higher readings than ultrasound, but after adjusting the finger cuff numbers to match ultrasound values, the device became reliable enough to track changes during tilt testing.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryCross-SectionalEditor reviewed

Cortical autonomic network connectivity predicts symptoms in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

Zinn, Mark A, Jason, Leonard A·International journal of psychophysiology : official journal of the International Organization of Psychophysiology·2021

This study looked at how the brain controls the autonomic nervous system (the part that manages heart rate, breathing, and other automatic functions) in people with ME/CFS. Researchers used special brain recordings to measure electrical activity in 34 ME/CFS patients and 34 healthy people at rest, then looked for differences in how different brain regions communicate with each other. They found that people with ME/CFS had different patterns of brain communication, and these differences were connected to specific symptoms like fatigue, thinking problems, and pain.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Cerebral blood flow remains reduced after tilt testing in myalgic encephalomyelitis/chronic fatigue syndrome patients.

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Clinical neurophysiology practice·2021

This study looked at blood flow to the brain in ME/CFS patients during and after a tilt test (where people are tilted upright). Researchers found that when ME/CFS patients were tilted, blood flow to their brain decreased abnormally, and importantly, it did not fully recover even after returning to lying down—unlike their heart's ability to recover. The severity of this delayed blood flow recovery was directly related to how sick the patient was, with the most severely ill patients showing the slowest recovery.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Cerebral blood flow is reduced in ME/CFS during head-up tilt testing even in the absence of hypotension or tachycardia: A quantitative, controlled study using Doppler echography.

van Campen, C Linda M C, Verheugt, Freek W A, Rowe, Peter C et al.·Clinical neurophysiology practice·2020

This study measured blood flow to the brain in ME/CFS patients while they were tilted upright for 30 minutes. Researchers found that blood flow to the brain dropped significantly more in ME/CFS patients (24-29%) compared to healthy people (7%), even in patients whose heart rate and blood pressure stayed normal. The more symptoms patients experienced from standing, the greater their blood flow reduction.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Hemodynamics during the 10-minute NASA Lean Test: evidence of circulatory decompensation in a subset of ME/CFS patients.

Lee, Jihyun, Vernon, Suzanne D, Jeys, Patricia et al.·Journal of translational medicine·2020

This study tested a simple 10-minute standing test called the NASA Lean Test in ME/CFS patients to understand heart and blood vessel problems that cause dizziness and weakness. Researchers found that patients who became sick more recently (within 4 years) showed signs of circulation problems during the test—their hearts beat faster and their blood pressure changed abnormally—while those sick for over 10 years showed fewer of these changes. The NASA Lean Test appears to be a useful tool that doctors can use to diagnose and monitor these circulation problems.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Reductions in Cerebral Blood Flow Can Be Provoked by Sitting in Severe Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients.

Campen, C Linda Mc van, Rowe, Peter C, Visser, Frans C·Healthcare (Basel, Switzerland)·2020

This study tested whether a simple sitting test could detect blood flow problems in the brains of severely ill ME/CFS patients. Researchers found that 90% of severe ME/CFS patients had significant drops in brain blood flow when sitting upright—dropping by about 24.5%—while healthy people's brain blood flow barely changed. This sitting test was easier to tolerate than standard tilt tests and could be useful for diagnosing blood flow problems in the most severely affected patients.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Clinically accessible tools for documenting the impact of orthostatic intolerance on symptoms and function in ME/CFS.

Lee, Jihyun, Wall, Pelle, Kimler, Chris et al.·Work (Reading, Mass.)·2020

This study looked at how much time ME/CFS patients can spend upright (standing or walking around) each day and how this relates to dizziness and other symptoms caused by orthostatic intolerance—a condition where symptoms get worse when standing or being active. Researchers compared 25 women with ME/CFS to 25 healthy women and found that ME/CFS patients spend far fewer hours upright and experience much worse symptoms that interfere with daily life. The study suggests that measuring upright hours and asking patients about orthostatic symptoms could be helpful tools for doctors diagnosing and managing ME/CFS.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Paradigm shift to disequilibrium in the genesis of orthostatic intolerance in patients with myalgic encephalomyelitis and chronic fatigue syndrome.

Miwa, Kunihisa, Inoue, Yukichi·International Journal of Cardiology. Hypertension·2020

This study looked at why people with ME/CFS struggle to stand up without feeling dizzy or unsteady. Researchers tested 72 patients and found that balance problems while standing (disequilibrium) were much more common in those who couldn't complete a 10-minute standing test than previously thought. The study suggests that poor balance, rather than just heart rate problems, may be a main reason why standing is so difficult for many ME/CFS patients.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryObservationalEditor reviewed

Prediction of Discontinuation of Structured Exercise Programme in Chronic Fatigue Syndrome Patients.

Kujawski, Sławomir, Cossington, Jo, Słomko, Joanna et al.·Journal of clinical medicine·2020

This study looked at why some people with ME/CFS could complete a gradual exercise programme while others had to stop. Researchers measured several body functions—like nervous system activity, reaction time, and heart rate—before the programme started. They found that people whose bodies showed higher stress responses and slower reaction times were more likely to drop out of the exercise programme.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCase-ControlEditor reviewed

Reduced heart rate variability predicts fatigue severity in individuals with chronic fatigue syndrome/myalgic encephalomyelitis.

Escorihuela, Rosa María, Capdevila, Lluís, Castro, Juan Ramos et al.·Journal of translational medicine·2020

This study measured how the heart rate varies between beats in people with ME/CFS compared to healthy people. Researchers found that people with ME/CFS have less variation in their heart rate and that this reduced variation is connected to how severe their fatigue is. The findings suggest that an overactive stress response in the nervous system may contribute to fatigue severity.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Autonomic Phenotypes in Chronic Fatigue Syndrome (CFS) Are Associated with Illness Severity: A Cluster Analysis.

Słomko, Joanna, Estévez-López, Fernando, Kujawski, Sławomir et al.·Journal of clinical medicine·2020

This study looked at 131 ME/CFS patients to see if different types of autonomic nervous system problems (the system that controls heart rate, blood pressure, and digestion) exist. Researchers found four distinct patterns: some patients had sympathetic overactivity with dysfunction, some had sympathetic symptoms alone, some had parasympathetic issues, and some had an imbalance between the two systems. Patients with sympathetic overactivity had the most severe symptoms and worst quality of life, while those with balanced autonomic function were younger, less fatigued, and reported better quality of life.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceObservationalEditor reviewed

Parasympathetic activity is reduced during slow-wave sleep, but not resting wakefulness, in patients with chronic fatigue syndrome.

Fatt, Scott J, Beilharz, Jessica E, Joubert, Michael et al.·Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine·2020

This study found that people with ME/CFS have reduced calming nervous system activity during deep sleep, compared to healthy people. This overactive state during sleep—even when the brain should be resting—is linked to poor sleep quality and feeling unwell. The findings suggest that the body's inability to fully relax during sleep may be a key problem in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Orthostatic intolerance in chronic fatigue syndrome.

Garner, Richard, Baraniuk, James N·Journal of translational medicine·2019

This study looked at dizziness and lightheadedness symptoms in ME/CFS patients when lying down versus standing up. Researchers found that these symptoms were very common in ME/CFS (occurring in 72% of patients when standing) and that they often happened even while lying down—something doctors don't usually check for. Importantly, these symptoms weren't simply caused by a rapid heart rate, suggesting a different mechanism is at play in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceLongitudinalEditor reviewed

Long Term Follow up of Young People With Chronic Fatigue Syndrome Attending a Pediatric Outpatient Service.

Rowe, Katherine S·Frontiers in pediatrics·2019

This study followed 784 young people with ME/CFS for an average of 8 years to understand how the illness progresses over time. About half of the young people reported recovery within 5 years, and by 10 years, 68% reported feeling recovered. Most young people improved in their ability to function daily, though a small group (5%) remained very unwell. Having supportive doctors, staying involved in school with flexible accommodations, and developing personal management plans were all important for long-term improvement.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Associations Between Autonomic and Orthostatic Self-report and Physician Ratings of Orthostatic Intolerance in Youth.

Schultz, Katlin R, Katz, Ben Z, Bockian, Neil R et al.·Clinical therapeutics·2019

This study looked at whether what young people with ME/CFS report feeling about dizziness and heart symptoms matches what doctors measure during physical exams. Researchers compared answers from questionnaires with actual measurements of blood pressure and heart rate changes. They found that while patients reported these symptoms, the physical measurements didn't always show the same problems, suggesting current testing methods may miss real autonomic problems in young ME/CFS patients.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryObservationalEditor reviewed

Relationship Between Exercise-induced Oxidative Stress Changes and Parasympathetic Activity in Chronic Fatigue Syndrome: An Observational Study in Patients and Healthy Subjects.

Polli, Andrea, Van Oosterwijck, Jessica, Nijs, Jo et al.·Clinical therapeutics·2019

This study looked at whether oxidative stress (cellular damage from normal metabolism) is related to pain in ME/CFS patients, and how it connects to the vagus nerve, which helps control the body's relaxation response. Researchers had ME/CFS patients and healthy people do a mild exercise test and measured their pain, oxidative stress levels, and nerve activity before and after. They found that oxidative stress was linked to pain in ME/CFS patients, but unlike healthy people, ME/CFS patients didn't show improvements in pain or oxidative stress after exercise.

Pain and SensitizationAutonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Impairments in cognitive performance in chronic fatigue syndrome are common, not related to co-morbid depression but do associate with autonomic dysfunction.

Robinson, Lucy J, Gallagher, Peter, Watson, Stuart et al.·PloS one·2019

This study found that people with ME/CFS often experience slowing in thinking speed and processing information, particularly in tasks requiring quick reactions. Importantly, these cognitive difficulties are not caused by depression—even patients without depression showed the same thinking problems. The researchers discovered that problems with heart rate regulation (how the body's autonomic nervous system works) were linked to these cognitive difficulties.

Autonomic Nervous SystemCognitive Impairment
E2 ModeratePEM requiredPreliminaryCase-ControlEditor reviewed

Autonomic Nervous System Functioning Related to Nocturnal Sleep in Patients With Chronic Fatigue Syndrome Compared to Tired Controls.

Orjatsalo, Maija, Alakuijala, Anniina, Partinen, Markku·Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine·2018

This study examined how the nervous system controls heart rate and blood pressure during sleep in ME/CFS patients compared to people without the condition. Researchers found that ME/CFS patients showed unusual patterns during sleep: their sympathetic nervous system (the 'fight or flight' system) was more active than normal, while their parasympathetic nervous system (the 'rest and digest' system) was less active, especially during deep sleep. This abnormal nervous system activity during sleep may help explain why ME/CFS patients often wake up feeling unrefreshed.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

The etiologic relation between disequilibrium and orthostatic intolerance in patients with myalgic encephalomyelitis (chronic fatigue syndrome).

Miwa, Kunihisa, Inoue, Yukichi·Journal of cardiology·2018

This study looked at 44 ME/CFS patients to understand why they struggle to stay upright (orthostatic intolerance). Researchers found that balance problems—difficulty staying steady when standing with eyes closed—were common and seemed to make orthostatic intolerance worse. Patients with balance problems were more likely to have trouble completing a 10-minute standing test than those with only heart rate changes, suggesting balance issues may be just as important as blood pressure and heart rate problems in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Circadian rhythm abnormalities and autonomic dysfunction in patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis.

Cambras, Trinitat, Castro-Marrero, Jesús, Zaragoza, Maria Cleofé et al.·PloS one·2018

This study compared daily activity patterns and skin temperature regulation in 10 women with ME/CFS and 10 healthy women over a week in both winter and summer. While sleep patterns were similar between groups, people with ME/CFS had lower overall daily activity levels and their bodies showed weaker responses to the normal daily rhythm patterns that healthy people display (like a post-lunch energy dip). The findings suggest that ME/CFS may involve problems with how the body's internal clock and temperature regulation systems work.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryCross-SectionalEditor reviewed

Blood Volume Status in ME/CFS Correlates With the Presence or Absence of Orthostatic Symptoms: Preliminary Results.

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Frontiers in pediatrics·2018

This study measured the amount of blood circulating in the bodies of 20 adults with ME/CFS and found that those with symptoms of dizziness or lightheadedness when standing up had significantly less blood volume than those without these symptoms. On average, all ME/CFS patients had about 11 milliliters less blood per kilogram of body weight than expected, but the drop was much more pronounced in patients with orthostatic symptoms. This finding suggests that reduced blood volume may be connected to specific symptoms some ME/CFS patients experience.

Autonomic Nervous System
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Poor self-reported sleep quality and health-related quality of life in patients with chronic fatigue syndrome/myalgic encephalomyelitis.

Castro-Marrero, Jesús, Zaragozá, Maria C, González-Garcia, Sergio et al.·Journal of sleep research·2018

This study looked at sleep problems in 1,455 Spanish ME/CFS patients and found that nearly all of them reported poor sleep quality that wasn't refreshing, even when they slept. The researchers discovered that poor sleep was strongly linked to worse pain, fatigue, anxiety, depression, and lower quality of life overall. Several factors—including pain intensity, mood problems, fibromyalgia, and autonomic nervous system dysfunction—were particularly associated with sleep difficulties.

Pain and SensitizationSleepAutonomic Nervous System
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The effects of warm water immersion on blood pressure, heart rate and heart rate variability in people with chronic fatigue syndrome.

Parker, Romy, Higgins, Zeenath, Mlombile, Zandiswa N P et al.·The South African journal of physiotherapy·2018

This study looked at how warm water bathing affects heart function in people with ME/CFS compared to healthy people. Researchers found that people with ME/CFS had less stable heart rate patterns before entering warm water, but this improved during the water immersion. The heart rate stayed slightly elevated in the ME/CFS group even after leaving the water. Overall, warm water immersion appeared safe and may help with managing ME/CFS symptoms.

Autonomic Nervous System
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Intracranial compliance is associated with symptoms of orthostatic intolerance in chronic fatigue syndrome.

Finkelmeyer, Andreas, He, Jiabao, Maclachlan, Laura et al.·PloS one·2018

Many people with ME/CFS experience dizziness or lightheadedness when standing up—a condition called orthostatic intolerance. This study used brain imaging to measure how well the brain's blood vessels and fluid systems adjust to position changes. Researchers found that ME/CFS patients with worse symptoms had less flexible brain spaces and higher blood flow at rest, suggesting their brains may struggle to maintain proper blood flow when standing.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Latent class analysis of a heterogeneous international sample of patients with myalgic encephalomyelitis/chronic fatigue syndrome.

Huber, Kayla A, Sunnquist, Madison, Jason, Leonard A·Fatigue : biomedicine, health & behavior·2018

This study looked at 1,210 ME/CFS patients to see if there are different types or subtypes of the illness based on their symptoms. Researchers found six distinct groups of patients, each experiencing different combinations of symptoms like heart and blood pressure problems, dizziness when standing, and digestive issues. Importantly, patients in different groups had very different abilities to function in daily life, suggesting that tailored treatment approaches might work better than one-size-fits-all care.

Autonomic Nervous System
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Low Sensitivity of Abbreviated Tilt Table Testing for Diagnosing Postural Tachycardia Syndrome in Adults With ME/CFS.

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Frontiers in pediatrics·2018

Many people with ME/CFS experience dizziness and rapid heartbeat when standing up, a condition called POTS. This study found that when doctors use shortened tilt table tests (lasting only 2 minutes) to diagnose POTS, they miss more than half of the patients who actually have it. The researchers recommend using the full 10-minute test instead of the abbreviated version to properly identify POTS in ME/CFS patients.

Autonomic Nervous System
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Cardiovascular characteristics of chronic fatigue syndrome.

Bozzini, Sara, Albergati, Andrea, Capelli, Enrica et al.·Biomedical reports·2018

This study looked at heart and blood pressure problems in people with ME/CFS. Researchers found that patients with ME/CFS tend to have lower blood pressure than expected, which may explain some common symptoms like dizziness, fatigue, and difficulty concentrating. Most other heart measurements were similar between people with and without ME/CFS.

Autonomic Nervous System
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Postural orthostatic tachycardia is not a useful diagnostic marker for chronic fatigue syndrome.

Roerink, M E, Lenders, J W M, Schmits, I C et al.·Journal of internal medicine·2017

This study tested whether a condition called POTS (postural orthostatic tachycardia syndrome)—where heart rate increases too much when standing—is a reliable marker for ME/CFS. Researchers found that POTS was equally common in ME/CFS patients and in people with fatigue who don't have ME/CFS, suggesting POTS is not a useful diagnostic tool for ME/CFS. The study did find that adolescents with both conditions responded less well to cognitive behavioral therapy than those with ME/CFS alone.

Autonomic Nervous System
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Stress vulnerability in adolescents with chronic fatigue syndrome: experimental study investigating heart rate variability and skin conductance responses.

Rimes, Katharine A, Lievesley, Kate, Chalder, Trudie·Journal of child psychology and psychiatry, and allied disciplines·2017

This study looked at how adolescents with ME/CFS respond to stress compared to young people with asthma and healthy teenagers. Researchers measured physical stress responses (heart rate and skin sweating) while young people gave a speech. Adolescents with ME/CFS showed signs of being more stressed before, during, and after the task, and their bodies took longer to calm down afterward compared to the other groups.

Autonomic Nervous System
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Are current chronic fatigue syndrome criteria diagnosing different disease phenotypes?

Maclachlan, Laura, Watson, Stuart, Gallagher, Peter et al.·PloS one·2017

This study looked at whether different diagnostic criteria for ME/CFS are actually identifying the same disease or different versions of it. Researchers tested 49 ME/CFS patients and 10 healthy controls using questionnaires and objective tests of heart function and thinking ability. They found that patients reported more autonomic and cognitive symptoms than controls, but objective heart tests didn't show clear differences—though different patient subgroups did show different levels of impairment on cognitive testing.

Autonomic Nervous SystemDiagnosticsCognitive Impairment
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Down-regulation of renin-aldosterone and antidiuretic hormone systems in patients with myalgic encephalomyelitis/chronic fatigue syndrome.

Miwa, Kunihisa·Journal of cardiology·2017

This study found that ME/CFS patients have smaller hearts and lower levels of certain hormones that control blood volume and fluid balance compared to healthy people. When researchers gave half the ME/CFS patients a synthetic hormone called desmopressin for five days, about half of them felt better, with less dizziness when standing and improved ability to do daily activities.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryObservationalEditor reviewed

Variability of postural orthostatic tachycardia in patients with myalgic encephalomyelitis and orthostatic intolerance.

Miwa, Kunihisa·Heart and vessels·2016

This study looked at how the hearts and nervous systems of 24 ME/CFS patients with orthostatic intolerance (dizziness or fatigue when standing) behaved on their "good days" versus "bad days." Researchers found that on bad days, patients' hearts raced more when standing up, they couldn't stand as long, and their hearts pumped less blood—suggesting their nervous systems were working abnormally, sometimes overactive and sometimes underactive.

Autonomic Nervous System
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Reduced cardiac volumes in chronic fatigue syndrome associate with plasma volume but not length of disease: a cohort study.

Newton, Julia L, Finkelmeyer, Andreas, Petrides, George et al.·Open heart·2016

This study found that people with ME/CFS have smaller hearts and lower blood volumes than healthy people. Interestingly, these differences were not related to how long someone had been sick, suggesting the heart changes are not simply from being inactive. Patients with more severe fatigue tended to have lower plasma volume (the liquid part of blood), which might be a target for future treatment.

Autonomic Nervous System
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Autonomic correlations with MRI are abnormal in the brainstem vasomotor centre in Chronic Fatigue Syndrome.

Barnden, Leighton R, Kwiatek, Richard, Crouch, Benjamin et al.·NeuroImage. Clinical·2016

This study examined whether blood pressure and heart rate patterns in ME/CFS patients are connected to differences in how their brains are structured or functioning. Researchers used 24-hour blood pressure monitoring and brain MRI scans in 25 ME/CFS patients and 25 healthy people, looking for correlations between the two. They found that ME/CFS patients showed unusual patterns in how their brainstem—the part of the brain that controls automatic functions like heart rate and blood pressure—communicated with other brain regions, suggesting a communication problem rather than structural damage.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Cardiac dysfunction and orthostatic intolerance in patients with myalgic encephalomyelitis and a small left ventricle.

Miwa, Kunihisa·Heart and vessels·2015

This study looked at heart function in 40 ME/CFS patients compared to 40 healthy people. Researchers found that ME/CFS patients frequently had smaller hearts and difficulty standing up without dizziness or other symptoms (orthostatic intolerance). The smaller heart size appeared to pump less blood with each beat, which may explain why patients struggle with upright posture and fatigue.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryObservationalEditor reviewed

Multivitamin mineral supplementation in patients with chronic fatigue syndrome.

Maric, Daniela, Brkic, Snezana, Tomic, Slavica et al.·Medical science monitor : international medical journal of experimental and clinical research·2014

This study tested whether taking a multivitamin and mineral supplement could help women with ME/CFS feel better. Thirty-eight women took the supplement for 2 months, and researchers measured changes in fatigue, sleep, headaches, and other symptoms. Most symptoms improved notably, including less fatigue and better sleep, though overall quality of life scores did not change.

SleepAutonomic Nervous System
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Heart rate variability during sleep and subsequent sleepiness in patients with chronic fatigue syndrome.

Togo, Fumiharu, Natelson, Benjamin H·Autonomic neuroscience : basic & clinical·2013

This study looked at how the heart's rhythm changes during sleep in ME/CFS patients compared to healthy people, and whether these changes relate to feeling more or less tired after sleep. Researchers found that some ME/CFS patients who woke up feeling sleepier had different heart rhythm patterns during deep sleep than healthy controls, even though standard sleep measurements looked normal. This suggests the nervous system's control of the heart during sleep might be disrupted in ME/CFS, which could contribute to unrefreshing sleep.

SleepAutonomic Nervous System
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Is chronic fatigue syndrome in older patients a different disease? -- a clinical cohort study.

Lewis, Ieuan, Pairman, Jessie, Spickett, Gavin et al.·European journal of clinical investigation·2013

This study compared ME/CFS symptoms and nervous system function in older patients (age 50+) versus younger patients (ages 16-29). Researchers found that older patients experienced more severe fatigue and depression, along with greater imbalance in their autonomic nervous system—the system that controls heart rate, blood pressure, and other automatic body functions. The results suggest that ME/CFS may present differently and more severely in older adults.

Autonomic Nervous System
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Clinical characteristics of a novel subgroup of chronic fatigue syndrome patients with postural orthostatic tachycardia syndrome.

Lewis, I, Pairman, J, Spickett, G et al.·Journal of internal medicine·2013

Some ME/CFS patients also have POTS (a condition where the heart rate and blood pressure don't adjust properly when standing up). This study found that ME/CFS patients with POTS are younger, experience less severe fatigue and depression, and have different patterns of daytime sleepiness compared to ME/CFS patients without POTS. A simple combination of two questionnaires can accurately identify which ME/CFS patients have POTS, potentially helping doctors decide who needs additional testing and treatment.

Autonomic Nervous System
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Relationship between autonomic cardiovascular control, case definition, clinical symptoms, and functional disability in adolescent chronic fatigue syndrome: an exploratory study.

Wyller, Vegard B, Helland, Ingrid B·BioPsychoSocial medicine·2013

This study looked at how the nervous system controls heart rate in teenagers with ME/CFS and how this relates to their symptoms and disability. Researchers tested 38 teenagers using a tilt test (lying flat then tilting upright) while measuring heart rate changes, and asked them about their symptoms. They found that disability in ME/CFS comes from multiple symptoms—not just fatigue—and that problems with heart rate control are linked to certain symptoms like brain fog and sensitivity to stimulation.

Autonomic Nervous SystemCognitive Impairment
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Reduced cardiac vagal modulation impacts on cognitive performance in chronic fatigue syndrome.

Beaumont, Alison, Burton, Alexander R, Lemon, Jim et al.·PloS one·2012

This study examined whether problems with the heart's automatic nervous system (which controls heart rate) are connected to cognitive difficulties in ME/CFS patients. Researchers measured heart rate variability—the natural variation in time between heartbeats—while 30 ME/CFS patients and 40 healthy controls performed thinking tasks. ME/CFS patients showed slower thinking speeds and unusual heart rate patterns, and their reduced heart rate variability was linked to their cognitive slowness.

Autonomic Nervous SystemCognitive Impairment
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Impaired blood pressure variability in chronic fatigue syndrome--a potential biomarker.

Frith, J, Zalewski, P, Klawe, J J et al.·QJM : monthly journal of the Association of Physicians·2012

ME/CFS is often associated with problems in the autonomic nervous system, which controls heart rate and blood pressure. This study measured how heart rate and blood pressure respond to position changes in 68 ME/CFS patients and 68 healthy controls. The researchers found that ME/CFS patients showed abnormal patterns in blood pressure variability that could potentially be used as a diagnostic test.

Autonomic Nervous System
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Chronic fatigue syndrome and impaired peripheral pulse characteristics on orthostasis--a new potential diagnostic biomarker.

Allen, John, Murray, Alan, Di Maria, Costanzo et al.·Physiological measurement·2012

This study tested a new way to measure how the heart and blood vessels respond when people stand up, using a painless light-based sensor on the ears, fingers, and toes. Researchers found that people with ME/CFS had a weaker blood vessel response to standing compared to healthy controls, which could potentially be used as an objective test to help diagnose ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCase-ControlEditor reviewed

Sleep-wake behavior in chronic fatigue syndrome.

Rahman, Khairunnessa, Burton, Alexander, Galbraith, Sally et al.·Sleep·2011

Researchers wanted to know if ME/CFS is caused by problems with the body's internal biological clock. They studied 15 people with ME/CFS and 15 healthy controls for 5 days, measuring sleep patterns, daily activity, stress hormone levels, and heart function. While people with ME/CFS reported worse fatigue, sleep problems, and pain, the researchers found no differences in actual sleep patterns or biological rhythms between the groups.

Autonomic Nervous System
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A brain MRI study of chronic fatigue syndrome: evidence of brainstem dysfunction and altered homeostasis.

Barnden, Leighton R, Crouch, Benjamin, Kwiatek, Richard et al.·NMR in biomedicine·2011

This study used specialized brain imaging (MRI) to compare 25 people with ME/CFS to 25 healthy controls, looking at brain structure and how it related to fatigue severity and other symptoms. Researchers found that people with ME/CFS showed differences in brainstem volume (a critical part of the brain controlling basic functions) that correlated with how long fatigue had lasted, and unusual patterns in how blood pressure related to brainstem structure. These findings suggest ME/CFS may involve damage to a specific brain region that disrupts the body's automatic control systems.

Autonomic Nervous System
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Physical activity intensity but not sedentary activity is reduced in chronic fatigue syndrome and is associated with autonomic regulation.

Newton, J L, Pairman, J, Hallsworth, K et al.·QJM : monthly journal of the Association of Physicians·2011

This study looked at how much people with ME/CFS move around during the day compared to healthy people. Researchers found that people with ME/CFS do less intense physical activity (like brisk walking or exercise) than healthy controls, even though they spend similar amounts of time sitting. The study also found that reduced physical activity was linked to problems with heart rate regulation in ME/CFS patients.

Autonomic Nervous System
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Small heart with low cardiac output for orthostatic intolerance in patients with chronic fatigue syndrome.

Miwa, Kunihisa, Fujita, Masatoshi·Clinical cardiology·2011

This study found that ME/CFS patients who experience dizziness or fainting when standing up (orthostatic intolerance) have smaller hearts and pump less blood with each beat compared to ME/CFS patients without these symptoms and healthy people. The researchers used ultrasound imaging to measure heart size and function in different groups and discovered that about half of ME/CFS patients with orthostatic intolerance had unusually small left heart chambers.

Autonomic Nervous System
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Fatigue severity remains stable over time and independently associated with orthostatic symptoms in chronic fatigue syndrome: a longitudinal study.

Jones, D E J, Gray, J, Frith, J et al.·Journal of internal medicine·2011

This study followed ME/CFS patients over 4 years to see how their fatigue changed. Researchers found that while some patients improved and others got worse, the overall severity of fatigue stayed relatively stable for most people. Importantly, fatigue was most closely linked to standing-related symptoms (dizziness, lightheadedness) and mood changes like depression and anxiety.

Autonomic Nervous System
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Reduced heart rate variability predicts poor sleep quality in a case-control study of chronic fatigue syndrome.

Burton, A R, Rahman, K, Kadota, Y et al.·Experimental brain research·2010

People with ME/CFS often report poor sleep quality. This study measured heart rate patterns during sleep in 20 patients with ME/CFS and 20 healthy controls, finding that ME/CFS patients had much lower heart rate variability (natural changes in heart rate) during sleep. The researchers concluded that this reduced variability—suggesting the nervous system stays "on high alert" even at night—is closely linked to their sleep problems.

Autonomic Nervous System
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Impaired cardiovascular response to standing in chronic fatigue syndrome.

Hollingsworth, Kieren G, Jones, David E J, Taylor, Roy et al.·European journal of clinical investigation·2010

This study found that people with ME/CFS have abnormal heart function when standing up, and their heart and muscle cells struggle to produce energy efficiently. Researchers used specialized scans to measure energy metabolism in the heart and muscles, and found that about one-third of ME/CFS patients showed significant heart energy problems. When standing, ME/CFS patients had stronger heart contractions and more symptoms compared to healthy controls, suggesting their bodies are working much harder to maintain blood flow.

Autonomic Nervous System
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Orthostatic symptoms predict functional capacity in chronic fatigue syndrome: implications for management.

Costigan, A, Elliott, C, McDonald, C et al.·QJM : monthly journal of the Association of Physicians·2010

This study found that ME/CFS patients have much greater difficulty with daily activities compared to healthy people. Among ME/CFS patients, those who experience dizziness or lightheadedness when standing up (orthostatic symptoms) had the most trouble with physical functioning. The researchers suggest that treating these standing-related symptoms might help patients do more in their daily lives.

Autonomic Nervous SystemCognitive Impairment
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Coenzyme Q10 deficiency in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is related to fatigue, autonomic and neurocognitive symptoms and is another risk factor explaining the early mortality in ME/CFS due to cardiovascular disorder.

Maes, Michael, Mihaylova, Ivanka, Kubera, Marta et al.·Neuro endocrinology letters·2009

This study found that people with ME/CFS have significantly lower levels of Coenzyme Q10 (CoQ10), a substance that helps cells produce energy, compared to healthy people. Nearly 45% of ME/CFS patients had CoQ10 levels below what was found in any of the healthy control group. Low CoQ10 was connected to worse fatigue, problems with heart and blood pressure regulation, and difficulty with thinking and memory.

Autonomic Nervous SystemCognitive Impairment
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Lower ambulatory blood pressure in chronic fatigue syndrome.

Newton, Julia L, Sheth, Amish, Shin, Jane et al.·Psychosomatic medicine·2009

This study measured blood pressure patterns over 24 hours in people with ME/CFS, healthy volunteers, and people with a liver disease that also causes fatigue. The researchers found that ME/CFS patients had lower blood pressure than healthy people and their blood pressure did not drop as much during sleep as it normally should. Higher fatigue levels were linked to these abnormal blood pressure patterns.

Autonomic Nervous System
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Cardiovascular dysfunction with low cardiac output due to a small heart in patients with chronic fatigue syndrome.

Miwa, Kunihisa, Fujita, Masatoshi·Internal medicine (Tokyo, Japan)·2009

This study found that many ME/CFS patients experience heart-related symptoms like shortness of breath, chest pain, fainting, and dizziness. Using heart imaging tests, researchers discovered that about one-third of ME/CFS patients had smaller-than-normal hearts that pump less blood than expected, which may contribute to their fatigue and other symptoms.

Autonomic Nervous System
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A matched case control study of orthostatic intolerance in children/adolescents with chronic fatigue syndrome.

Galland, Barbara C, Jackson, Pamela M, Sayers, Rachel M et al.·Pediatric research·2008

This study looked at how the hearts and blood vessels of children and teenagers with ME/CFS respond when they stand up or are tilted upright. Researchers compared 26 young people with ME/CFS to similar healthy controls using a tilt table test. They found that children with ME/CFS were much more likely to experience dizziness and abnormal heart rate responses during the test, suggesting their bodies struggle to regulate blood pressure and heart function when upright.

Autonomic Nervous System
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Small heart syndrome in patients with chronic fatigue syndrome.

Miwa, Kunihisa, Fujita, Masatoshi·Clinical cardiology·2008

This study found that people with ME/CFS are more likely to have a smaller heart than healthy people. Researchers used chest X-rays and heart ultrasounds to measure heart size in 56 ME/CFS patients under age 50 and compared them to 38 healthy controls. Patients with both ME/CFS and a small heart also experienced more symptoms like dizziness when standing, cold feet, and heart rhythm irregularities.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Enhanced vagal withdrawal during mild orthostatic stress in adolescents with chronic fatigue.

Wyller, Vegard Bruun, Barbieri, Riccardo, Thaulow, Erik et al.·Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc·2008

This study looked at how the nervous system controls heart rate in adolescents with ME/CFS, particularly during mild physical stress (tilting on a table). Researchers found that teenagers with ME/CFS showed an unusual heart rate pattern—their bodies shifted too quickly toward stress-mode responses compared to healthy teens. This suggests their autonomic nervous system, which normally helps regulate heart rate and blood pressure, may not be working properly.

Autonomic Nervous System
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Sympathetic cardiovascular control during orthostatic stress and isometric exercise in adolescent chronic fatigue syndrome.

Wyller, Vegard Bruun, Saul, J Philip, Walløe, Lars et al.·European journal of applied physiology·2008

This study looked at how the bodies of adolescents with ME/CFS respond to physical stress, specifically when lying down while pressure is applied to the legs and while squeezing a hand grip. Researchers found that ME/CFS patients had higher heart rates and stress hormone levels even at rest, and their cardiovascular system overreacted to the leg pressure test but underreacted during the hand grip exercise compared to healthy teenagers.

Autonomic Nervous System
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Postural orthostatic tachycardia syndrome is an under-recognized condition in chronic fatigue syndrome.

Hoad, A, Spickett, G, Elliott, J et al.·QJM : monthly journal of the Association of Physicians·2008

This study looked at whether people with ME/CFS have a condition called POTS (postural orthostatic tachycardia syndrome), which causes the heart to beat much faster when standing up. Researchers tested 59 ME/CFS patients and compared them to 52 healthy people, measuring heart rate changes when they stood up. They found that 27% of ME/CFS patients had POTS, compared to only 9% of healthy controls, suggesting this condition is common but often missed in ME/CFS.

Autonomic Nervous System
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Usefulness of an abnormal cardiovascular response during low-grade head-up tilt-test for discriminating adolescents with chronic fatigue from healthy controls.

Wyller, Vegard Bruun, Due, Reidar, Saul, J Philip et al.·The American journal of cardiology·2007

This study tested how the hearts of adolescents with ME/CFS respond to mild physical stress (tilting the body slightly upright for 15 minutes) compared to healthy teenagers. Researchers found that young people with ME/CFS had abnormal heart and blood vessel responses during this test—their hearts beat faster, their blood pressure increased more, and their stroke volume (amount of blood pumped per heartbeat) decreased more than in healthy controls. These differences suggest that ME/CFS involves problems with how the body regulates blood flow and heart function during even mild stress.

Autonomic Nervous System
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Higher heart rate and reduced heart rate variability persist during sleep in chronic fatigue syndrome: a population-based study.

Boneva, Roumiana S, Decker, Michael J, Maloney, Elizabeth M et al.·Autonomic neuroscience : basic & clinical·2007

This study found that people with ME/CFS have a faster heart rate and less heart rate variability (natural changes in heartbeat speed) during sleep compared to healthy people. These differences suggest that the nervous system in ME/CFS patients stays more activated even during sleep, which may be related to chemical imbalances in the body.

SleepAutonomic Nervous System
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Sympathetic predominance of cardiovascular regulation during mild orthostatic stress in adolescents with chronic fatigue.

Wyller, Vegard B, Saul, J P, Amlie, Jan P et al.·Clinical physiology and functional imaging·2007

This study looked at how the nervous system controls the heart and blood vessels in teenagers with ME/CFS when their bodies experience mild stress (tilting on a bed). Researchers found that adolescents with ME/CFS showed an exaggerated sympathetic nervous system response—meaning their "fight or flight" system kicked in too strongly compared to healthy teenagers. This suggests the body's automatic control of heart rate and blood pressure may not work normally in ME/CFS.

Autonomic Nervous System
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Symptoms of autonomic dysfunction in chronic fatigue syndrome.

Newton, J L, Okonkwo, O, Sutcliffe, K et al.·QJM : monthly journal of the Association of Physicians·2007

This study looked at whether people with ME/CFS have problems with their autonomic nervous system (the part that controls automatic body functions like heart rate and blood pressure). Researchers used a questionnaire called COMPASS to measure autonomic symptoms in ME/CFS patients and healthy controls. They found that autonomic dysfunction symptoms were significantly more common in ME/CFS patients and were linked to how severe their fatigue was.

Autonomic Nervous System
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[Estimation of fatigue state in patient with CFS using actigraph and R-R interval power spectrum analysis].

Tajima, Seiki, Kuratsune, Hirohiko, Yamaguti, Kouzi et al.·Nihon rinsho. Japanese journal of clinical medicine·2007

This study measured activity levels and sleep patterns in people with ME/CFS using wearable devices and heart rate analysis. Researchers found that ME/CFS patients had lower activity during waking hours, slept longer, experienced more frequent sleep disruptions, and showed abnormal nervous system activity during sleep compared to healthy people.

SleepAutonomic Nervous System
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Shortened QT interval: a distinctive feature of the dysautonomia of chronic fatigue syndrome.

Naschitz, Jochanan, Fields, Madeline, Isseroff, Hillel et al.·Journal of electrocardiology·2006

This study examined heart rhythm patterns in ME/CFS patients by measuring a specific electrical timing interval on EKGs (called the QT interval). Researchers found that people with ME/CFS had shorter QT intervals than healthy controls, both when lying down and during a head-up tilt test. This shortened interval appears to be linked to the autonomic nervous system problems common in ME/CFS.

Autonomic Nervous System
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Orthostatic instability in a population-based study of chronic fatigue syndrome.

Jones, James F, Nicholson, Ainsley, Nisenbaum, Rosane et al.·The American journal of medicine·2005

This study tested whether people with ME/CFS have problems with their body's ability to regulate blood pressure and heart rate when changing positions (like standing up). Researchers compared 58 people with ME/CFS to 55 healthy people using a tilt table test. Surprisingly, they found that both groups had similar rates of these problems, suggesting that this particular type of autonomic dysfunction may not be a primary cause of ME/CFS.

Autonomic Nervous System
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Electrodermal dissociation of chronic fatigue and depression: evidence for distinct physiological mechanisms.

Pazderka-Robinson, Hannah, Morrison, James W, Flor-Henry, Pierre·International journal of psychophysiology : official journal of the International Organization of Psychophysiology·2004

This study looked at how the bodies of people with ME/CFS and people with depression respond differently to their surroundings. Researchers measured skin conductance (how easily electricity travels across the skin) and skin temperature while participants performed a task. They found that people with ME/CFS had notably lower skin conductance levels and higher skin temperature compared to people with depression and healthy controls, suggesting these are two different conditions with different underlying biology.

Autonomic Nervous System
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Use of time-frequency analysis to investigate temporal patterns of cardiac autonomic response during head-up tilt in chronic fatigue syndrome.

Yoshiuchi, Kazuhiro, Quigley, Karen S, Ohashi, Kyoko et al.·Autonomic neuroscience : basic & clinical·2004

This study looked at how the nervous system that controls heart rate and blood pressure responds when people stand up from lying down. Researchers tested people with ME/CFS (with and without a condition called POTS), and compared them to healthy volunteers. They found that even ME/CFS patients without POTS showed subtle differences in how their heart rate changed during the standing test, suggesting their autonomic nervous system may not work quite normally.

Autonomic Nervous System
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Patterns of cardiovascular reactivity in disease diagnosis.

Naschitz, J E, Rosner, I, Rozenbaum, M et al.·QJM : monthly journal of the Association of Physicians·2004

This study looked at how the heart and blood vessels respond to changes in body position (lying down versus standing up) in people with ME/CFS compared to healthy people and those with other conditions. Researchers used a simple test where patients lie down and then tilt upright while measuring heart rate and blood vessel changes. They found that people with ME/CFS have a distinctive pattern of heart and blood vessel responses that could help doctors identify the condition.

Autonomic Nervous System
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Peripheral cholinergic function in humans with chronic fatigue syndrome, Gulf War syndrome and with illness following organophosphate exposure.

Khan, Faisel, Kennedy, Gwen, Spence, Vance A et al.·Clinical science (London, England : 1979)·2004

Researchers tested how blood vessels in the forearm respond to acetylcholine (a chemical messenger in the body) in people with ME/CFS, Gulf War illness, and pesticide exposure. They found that people with ME/CFS had an unusually strong vascular response to acetylcholine, but people with the other two conditions had normal responses. This suggests ME/CFS may involve a specific problem with how the body breaks down acetylcholine in blood vessels.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

The head-up tilt test with haemodynamic instability score in diagnosing chronic fatigue syndrome.

Naschitz, J E, Rosner, I, Rozenbaum, M et al.·QJM : monthly journal of the Association of Physicians·2003

Researchers developed a simple test using a tilting table to measure how well the body controls blood pressure and heart rate in ME/CFS patients. By tilting people upright and measuring these vital signs, they found a pattern (called a haemodynamic instability score) that appeared in ME/CFS patients but not in healthy people or those with other conditions. This test could help doctors confirm an ME/CFS diagnosis with objective measurements rather than relying only on symptoms.

Autonomic Nervous SystemDiagnostics
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A measure of heart rate variability is sensitive to orthostatic challenge in women with chronic fatigue syndrome.

Yamamoto, Yoshiharu, LaManca, John J, Natelson, Benjamin H·Experimental biology and medicine (Maywood, N.J.)·2003

This study tested whether a simple heart rhythm measurement during a tilt test could help diagnose ME/CFS. Researchers compared heart rate patterns in 24 women with ME/CFS and 22 healthy women while they lay down and then tilted upright for 10 minutes. They found that women with ME/CFS showed a distinctive abnormal change in their heart rhythm pattern during tilting that could identify about 9 out of 10 ME/CFS patients correctly.

Autonomic Nervous System
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Prolonged acetylcholine-induced vasodilatation in the peripheral microcirculation of patients with chronic fatigue syndrome.

Khan, Faisel, Spence, Vance, Kennedy, Gwen et al.·Clinical physiology and functional imaging·2003

This study looked at how blood vessels in the skin of ME/CFS patients respond to acetylcholine, a chemical messenger in the body. Researchers found that while the initial response was similar in patients and healthy controls, the blood vessels of ME/CFS patients took much longer to return to normal after the chemical was applied. This suggests that the way nerve signals control blood vessel function may be different in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Assessment of cardiovascular reactivity by fractal and recurrence quantification analysis of heart rate and pulse transit time.

Naschitz, J E, Rosner, I, Shaviv, N et al.·Journal of human hypertension·2003

Researchers tested how the hearts of people with ME/CFS respond to a simple physical challenge (tilting from lying down to sitting up). They measured heart rate and blood vessel responses using advanced mathematical analysis that detects patterns typically missed by standard methods. People with ME/CFS showed very different heart responses compared to healthy people and those with high blood pressure, suggesting their cardiovascular systems react abnormally to physical stress.

Autonomic Nervous System
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Effects of posttraumatic stress disorder on cardiovascular stress responses in Gulf War veterans with fatiguing illness.

Peckerman, Arnold, Dahl, Kristina, Chemitiganti, Rahul et al.·Autonomic neuroscience : basic & clinical·2003

This study looked at how the bodies of Gulf War veterans with chronic fatigue respond to stress, particularly focusing on heart rate and blood pressure changes. The researchers found that veterans who had both chronic fatigue and PTSD (post-traumatic stress disorder) showed unusual cardiovascular responses to mental tasks and changes in position, such as lower blood pressure increases and slower recovery. These abnormal responses were much less pronounced in fatigued veterans without PTSD, suggesting that PTSD may be an important factor in how the body reacts to stress in this population.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Fractal analysis and recurrence quantification analysis of heart rate and pulse transit time for diagnosing chronic fatigue syndrome.

Naschitz, Jochanan E, Sabo, Edmond, Naschitz, Shaul et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2002

This study tested a new way to diagnose ME/CFS by measuring how the heart and blood vessels respond to a simple tilt test (lying down then standing up). Researchers used mathematical analysis of heart rate patterns and blood flow timing to create a scoring system that could correctly identify ME/CFS patients 70% of the time. The test was safe and well-tolerated by participants.

Autonomic Nervous System
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Hemodynamics instability score in chronic fatigue syndrome and in non-chronic fatigue syndrome.

Naschitz, Jochanan E, Sabo, Edmond, Naschitz, Shaul et al.·Seminars in arthritis and rheumatism·2002

Researchers developed a simple scoring system to measure how much a person's blood pressure and heart rate fluctuate during a tilt test (where patients lie flat then are tilted upright). They found that ME/CFS patients had much more unstable blood pressure and heart rate compared to healthy people, people with other types of fatigue, and even people who faint unexpectedly. This instability might be a useful marker to help diagnose ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Impaired postural cerebral hemodynamics in young patients with chronic fatigue with and without orthostatic intolerance.

Tanaka, Hidetaka, Matsushima, Reiko, Tamai, Hiroshi et al.·The Journal of pediatrics·2002

This study measured how blood flow to the brain changes when young people with ME/CFS stand up, compared to healthy controls. Researchers found that many ME/CFS patients—especially those who feel dizzy or have a racing heart when standing—did not get the normal quick boost of oxygen to their brain that healthy people do. This suggests that problems with brain blood flow during position changes may be connected to ME/CFS symptoms.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Hemodynamic and neurohumoral responses to head-up tilt in patients with chronic fatigue syndrome.

Timmers, H J L M, Wieling, W, Soetekouw, P M M B et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2002

This study looked at whether ME/CFS patients have problems with blood pressure and heart rate control when standing up or tilting upright. Researchers tested 36 ME/CFS patients and 36 healthy people by tilting them upright for 40 minutes while measuring heart function and stress hormones. About 28% of ME/CFS patients had abnormal responses (like fainting symptoms or rapid heart rate), compared to 17% of healthy controls, though this difference was not statistically significant.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Hemodynamic instability in chronic fatigue syndrome: indices and diagnostic significance.

Naschitz, J E, Sabo, E, Naschitz, S et al.·Seminars in arthritis and rheumatism·2001

This study tested how the body's blood pressure and heart rate respond when patients stand up from lying down (a tilt test). Researchers found that people with ME/CFS have much more unstable cardiovascular responses compared to healthy people and those with other conditions. A mathematical score called the hemodynamic instability score (HIS) could correctly identify ME/CFS patients 97% of the time, suggesting this test might help doctors diagnose the condition.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryCross-SectionalEditor reviewed

Neurally mediated hypotension in fatigued Gulf War veterans: a preliminary report.

Davis, S D, Kator, S F, Wonnett, J A et al.·The American journal of the medical sciences·2000

This study tested whether fatigued Gulf War veterans have problems with blood pressure control when standing up quickly (a condition called neurally mediated hypotension), similar to what researchers have seen in ME/CFS patients. The researchers tilted 14 fatigued Gulf War veterans on a special table and compared their responses to two groups of unfatigued veterans and non-veterans. They found that fatigued veterans were more likely to experience dangerous drops in blood pressure during the test, suggesting their autonomic nervous system (the part that automatically controls heart rate and blood pressure) may not be working properly.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

The capnography head-up tilt test for evaluation of chronic fatigue syndrome.

Naschitz, J E, Rosner, I, Rozenbaum, M et al.·Seminars in arthritis and rheumatism·2000

This study tested whether a special tilt table test that measures blood pressure, heart rate, breathing, and carbon dioxide levels could help diagnose ME/CFS. Researchers compared 32 ME/CFS patients to 32 healthy people during this test. ME/CFS patients showed abnormal responses—like drops in blood pressure, increases in heart rate, faster breathing, and lower carbon dioxide levels—while healthy people did not, suggesting this test might help identify ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCase-ControlEditor reviewed

Results of isoproterenol tilt table testing in monozygotic twins discordant for chronic fatigue syndrome.

Poole, J, Herrell, R, Ashton, S et al.·Archives of internal medicine·2000

This study tested whether a condition called neurally mediated hypotension (a sudden drop in blood pressure) might be causing ME/CFS. Researchers compared identical twins where one had ME/CFS and one was healthy, using a tilt table test to measure blood pressure responses. They found that healthy twins and twins with ME/CFS had similar rates of this blood pressure problem, suggesting it is probably not a main cause of ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Autonomic function in patients with chronic fatigue syndrome.

Soetekouw, P M, Lenders, J W, Bleijenberg, G et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·1999

Researchers tested whether ME/CFS patients have problems with the part of the nervous system that automatically controls heart rate and blood pressure. They compared 37 ME/CFS patients to 38 healthy people using several tests (like standing up quickly, holding their breath, and doing mental math). The study found only minor differences, suggesting that major autonomic problems may not be the primary issue in ME/CFS, though some specific responses to stress were reduced.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Orthostatic intolerance in adolescent chronic fatigue syndrome.

Stewart, J M, Gewitz, M H, Weldon, A et al.·Pediatrics·1999

This study looked at how the bodies of adolescents with ME/CFS respond when they stand up or tilt upright. Researchers found that nearly all ME/CFS patients showed significant problems with this response, including rapid heart rate, blood pressure drops, and symptoms like dizziness and fainting. These problems were much more common in ME/CFS patients than in healthy teenagers or those with simple fainting disorders.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Cardiovascular response during head-up tilt in chronic fatigue syndrome.

LaManca, J J, Peckerman, A, Walker, J et al.·Clinical physiology (Oxford, England)·1999

This study tested how the hearts of ME/CFS patients respond to positional changes using a tilt table test, where participants lie flat then are gradually tilted upward for 45 minutes. While ME/CFS patients showed different baseline heart rates and heart pumping patterns compared to healthy controls, the overall frequency of fainting-like responses was similar between the two groups.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Orthostatic intolerance in the chronic fatigue syndrome.

Schondorf, R, Benoit, J, Wein, T et al.·Journal of the autonomic nervous system·1999

This study looked at whether ME/CFS patients experience problems with blood pressure and heart rate when standing up quickly, a condition called orthostatic intolerance. Researchers tested 75 ME/CFS patients and 48 healthy controls using a tilt table test and other physical challenges. They found that 40% of ME/CFS patients had orthostatic intolerance compared to fewer healthy controls, suggesting this may be an important symptom in some patients that could be treated.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Patterns of orthostatic intolerance: the orthostatic tachycardia syndrome and adolescent chronic fatigue.

Stewart, J M, Gewitz, M H, Weldon, A et al.·The Journal of pediatrics·1999

This study looked at how the hearts and blood pressure of adolescents with ME/CFS and a related condition called orthostatic tachycardia syndrome (OTS) respond when they stand up or are tilted upright. Researchers found that adolescents with ME/CFS had more severe problems with standing (like dizziness and fainting) than those with OTS, but the underlying patterns were quite similar. The study suggests that OTS may be a milder version of the same blood pressure and heart rate problems seen in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryReview-NarrativeEditor reviewed

Relationship Between Chronic Fatigue Syndrome and Neurally Mediated Hypotension.

Calkins, H, Rowe, PC·Cardiology in review·1998

This study explored a possible connection between ME/CFS and a condition called neurally mediated hypotension, where blood pressure drops suddenly due to problems with nerve signals that control blood vessels. Researchers found that when they treated patients for this blood pressure problem, about two-thirds of ME/CFS patients felt better. While these early results were promising, the study notes that larger, more rigorous trials were needed to confirm whether this treatment truly helps.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryObservationalEditor reviewed

Amplified amplitudes of circadian rhythms and nighttime hypotension in patients with chronic fatigue syndrome: improvement by inopamil but not by melatonin.

van de Luit, L, van der Meulen, J, Cleophas, T J et al.·Angiology·1998

This study found that people with ME/CFS have unusually large swings in heart rate and blood pressure throughout the day and night, even though the overall pattern matches healthy controls. Importantly, their nighttime blood pressure drops too low (below 100 mm Hg systolic), which may contribute to fatigue and other symptoms. When treated with a heart-strengthening medication called inopamil, nighttime blood pressure improved, but melatonin actually made it worse.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Long- and short-term blood pressure and RR-interval variability and psychosomatic distress in chronic fatigue syndrome.

Duprez, D A, De Buyzere, M L, Drieghe, B et al.·Clinical science (London, England : 1979)·1998

Researchers compared blood pressure and heart rate patterns in people with ME/CFS to healthy controls. They found that people with ME/CFS had normal blood pressure readings, but their heart rates were consistently higher. When lying down, people with ME/CFS also showed reduced variability in blood pressure patterns compared to healthy controls.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCase-ControlEditor reviewed

Autonomic testing in patients with chronic fatigue syndrome.

De Becker, P, Dendale, P, De Meirleir, K et al.·The American journal of medicine·1998

This study tested how the nervous system that controls heart rate and blood pressure works in ME/CFS patients compared to healthy people. Researchers found that ME/CFS patients had higher heart rates and stronger stress responses when standing up, suggesting their bodies may be overactive in certain stress situations. However, these findings did not fully explain why ME/CFS patients experience fatigue and problems with exercise.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCase-ControlEditor reviewed

Pathogenesis and management of delayed orthostatic hypotension in patients with chronic fatigue syndrome.

De Lorenzo, F, Hargreaves, J, Kakkar, V V·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·1997

Some ME/CFS patients experience dizziness or fainting when standing up, a condition called orthostatic hypotension. This study tested whether salt supplements could help 22 ME/CFS patients with this symptom. After 8 weeks, salt helped 11 patients feel better, but 10 patients' symptoms returned—and those 10 had lower levels of a hormone called renin that helps regulate blood pressure.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Does the chronic fatigue syndrome involve the autonomic nervous system?

Freeman, R, Komaroff, A L·The American journal of medicine·1997

This study tested whether ME/CFS patients have problems with their autonomic nervous system—the part of the nervous system that controls automatic functions like heart rate and blood pressure. Researchers found that ME/CFS patients had abnormal heart rate and blood pressure responses during standing and tilting tests, and their nervous system wasn't regulating these responses properly. The findings suggest that either deconditioning from reduced activity, a viral infection damaging the nervous system, or both could explain why many ME/CFS patients feel dizzy or faint when standing up.

Autonomic Nervous System
E2 ModeratePEM unclearWeak / uncertainCross-SectionalEditor reviewed

An investigation of sympathetic hypersensitivity in chronic fatigue syndrome.

Sendrowski, D P, Buker, E A, Gee, S S·Optometry and vision science : official publication of the American Academy of Optometry·1997

Researchers tested whether ME/CFS patients have unusually sensitive nerves that control pupil size, similar to what is seen in fibromyalgia. They applied eye drops to 29 ME/CFS patients and 33 healthy controls and measured how much the pupils dilated. The results showed no significant difference between the two groups, suggesting that ME/CFS patients do not have this type of nerve sensitivity.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Comparison of heart rate variability in patients with chronic fatigue syndrome and controls.

Yataco, A, Talo, H, Rowe, P et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·1997

Researchers tested whether ME/CFS patients have problems with their autonomic nervous system (the system that automatically controls heart rate, blood pressure, and other vital functions). They measured heart rate variability—natural variations in heart rate—in ME/CFS patients and healthy controls while lying down and standing up. They found that the heart rate patterns were similar between the two groups both at rest and when standing, suggesting that basic autonomic function may not be obviously different in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Vagal tone is reduced during paced breathing in patients with the chronic fatigue syndrome.

Sisto, S A, Tapp, W, Drastal, S et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·1995

This study looked at how the vagus nerve—which helps control heart rate and relaxation—works differently in people with ME/CFS compared to healthy people. Researchers had women with ME/CFS and healthy women breathe at different controlled rates while measuring their heart rate patterns. They found that people with ME/CFS had weaker vagal nerve activity overall, suggesting their nervous system may not be able to relax and recover as effectively as healthy people's.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCase-ControlEditor reviewed

The relationship between neurally mediated hypotension and the chronic fatigue syndrome.

Bou-Holaigah, I, Rowe, P C, Kan, J et al.·JAMA·1995

Researchers tested whether ME/CFS patients have an abnormal blood pressure response when standing upright. They tilted 23 ME/CFS patients and 14 healthy controls on a special table and monitored their vital signs. Nearly all ME/CFS patients showed an abnormal response, and about 9 patients felt much better after taking medications to treat low blood pressure.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Sympathetic overactivity in subjects complaining of unexplained fatigue.

Pagani, M, Lucini, D, Mela, G S et al.·Clinical science (London, England : 1979)·1994

This study examined how the nervous system controls heart rate in people with unexplained fatigue compared to healthy people. Using heart rate recordings, researchers found that fatigue patients showed an imbalance in their autonomic nervous system—specifically, the part that triggers the "fight or flight" response was overactive while the calming part was underactive, even at rest.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Ocular Symptoms in Long COVID: A Cross-Sectional Study.

Kaleem, Shayaan, Sawano, Mitsuaki, Arun, Adith S et al.·Clinical ophthalmology (Auckland, N.Z.)·2026

This study looked at eye problems in people with long COVID, comparing those who developed new eye symptoms (like blurred vision, dry eyes, or floaters) after infection with those who didn't. About 57% of the 595 participants reported new eye symptoms. People with eye symptoms had worse overall health, more financial struggles, and were more likely to have dysautonomia (problems with blood pressure and heart rate control) and ME/CFS.

Autonomic Nervous System
E2 ModeratePEM unclearPreliminaryCross-SectionalEditor reviewed

Disequilibrium, Rather than Postural Orthostatic Tachycardia Syndrome, Is the Primary Determinant of Orthostatic Intolerance in Patients with Long COVID.

Miwa, Kunihisa·Journal of clinical medicine·2026

Many long COVID patients experience dizziness and difficulty standing (orthostatic intolerance), but researchers found this is not usually caused by the heart racing when standing up (POTS). Instead, balance problems detected by simple standing tests were the main cause in these patients. When treated with an antibiotic or brain stimulation therapy, most patients with balance-related standing problems improved.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Characterization of Postural Orthostatic Tachycardia Syndrome in Long COVID: Self-reported Data From the LISTEN Study.

Al Mouslmani, Mohammad, Sawano, Mitsuaki, Arun, Adith S et al.·JACC. Advances·2025

This study looked at people with long COVID who also developed POTS (a condition where the heart rate spikes when standing up). Among nearly 600 long COVID patients, about 29% reported having POTS. People with both conditions reported significantly more symptoms—including dizziness, chest pain, extreme fatigue, difficulty exercising, and brain fog—and experienced worse overall health and quality of life compared to those with long COVID alone.

Autonomic Nervous SystemCognitive Impairment
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Autonomic Dysfunction and Low Cardio-Respiratory Fitness in Long-Term Post-COVID-19 Syndrome.

Cherneva, Radostina, Cherneva, Zheyna, Youroukova, Vania et al.·Biomedicines·2025

This study looked at 192 people who had COVID-19 to understand why some develop long-term fatigue and exercise problems. Researchers measured how well the heart adjusts during exercise and found that people with moderate-to-severe post-COVID symptoms had problems with their autonomic nervous system (the system that controls automatic body functions like heart rate). However, these nervous system problems didn't fully explain why patients had lower exercise capacity.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Chronotropic Incompetence in Non-Hospitalized Patients with Post-COVID-19 Syndrome.

Jimeno-Almazán, Amaya, Pallarés, Jesús G, Buendía-Romero, Ángel et al.·Journal of clinical medicine·2021

Some people who recover from COVID-19 experience persistent fatigue and difficulty exercising for months afterward. This study tested 32 people with long-lasting COVID symptoms and found that about 12% had a specific heart problem called chronotropic incompetence—their heart rate doesn't increase normally during exercise. This heart rhythm problem may explain why some patients struggle with exercise intolerance after COVID-19.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Shared autonomic phenotype of long COVID and myalgic encephalomyelitis/chronic fatigue syndrome.

Novak, Peter, Systrom, David M, Witte, Alexandra et al.·PloS one·2026

Researchers compared people with Long COVID and ME/CFS to healthy volunteers and found they share very similar patterns of nervous system dysfunction, including problems with blood flow to the brain when standing up, widespread autonomic problems, and nerve damage in the skin. While the two conditions show these striking similarities, the study couldn't identify a single test that clearly separates them from each other, suggesting they may develop through related mechanisms.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Small fiber neuropathy in the post-COVID condition and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical significance and diagnostic challenges.

Azcue, Naiara, Teijeira-Portas, Sara, Tijero-Merino, Beatriz et al.·European journal of neurology·2025

This study found that both long-COVID patients and people with ME/CFS show signs of damage to small nerve fibers in the eyes and altered sensation to heat, compared to healthy people. Researchers used specialized imaging and tests to measure nerve fiber structure and how well patients could detect temperature changes. The findings suggest that small fiber nerve damage may contribute to symptoms like pain and abnormal sensations in these conditions.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryObservationalEditor reviewed

Nonpelvic comorbid symptoms of 45 patients with pain of pelvic venous origin, before and after treatment.

Smith, Steven J, Smith, B Holly, Sichlau, Michael J et al.·Phlebology·2025

This study looked at 45 women with chronic pelvic pain caused by abnormal blood pooling in pelvic veins. These patients experienced many symptoms beyond pelvic pain—including brain fog, fatigue, migraines, constipation, and anxiety. After receiving a catheter-based procedure to fix the blood pooling, most of these systemic symptoms improved significantly (by 50% or more).

Pain and SensitizationAutonomic Nervous SystemCognitive Impairment
E2 ModeratePEM requiredPreliminaryCross-SectionalEditor reviewed

Exploratory study on autoantibodies to arginine-rich human peptides mimicking Epstein-Barr virus in women with post-COVID and myalgic encephalomyelitis/chronic fatigue syndrome.

Hoheisel, Friederike, Fleischer, Kathrin Maria, Rubarth, Kerstin et al.·Frontiers in immunology·2025

This study looked for certain antibodies in the blood of women with post-COVID and ME/CFS that might mistakenly attack the body's own proteins. The researchers found that patients with these conditions had more of these problematic antibodies than healthy people, and these antibodies were linked to common ME/CFS symptoms like fatigue, brain fog, pain, and autonomic problems. The results suggest that a virus (EBV) may trigger the immune system to attack human proteins that look similar to viral proteins.

Pain and SensitizationAutonomic Nervous SystemCognitive Impairment
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The Relationship Between Hemodynamic Responses During Head-Up Tilt Testing and Parameters of Infection in Post-COVID Syndrome, Chronic Fatigue Syndrome, and Late-Stage Lyme Disease.

Milovanovic, Branislav, Markovic, Nikola, Petrovic, Masa et al.·Viruses·2025

This study examined 1036 patients with post-COVID syndrome, chronic fatigue syndrome, and Lyme disease to understand why they experience dizziness and fainting when standing up. Researchers performed tilt-table tests (where patients lie on a table that tilts upward) and checked for signs of past or ongoing infections through blood tests. They found that patients with evidence of multiple past infections were more likely to have abnormal responses during the tilt test, suggesting that lingering effects from infections may affect the nervous system's ability to control blood pressure and heart rate.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Autonomic symptom burden, comorbidities and quality of life in women with Hypermobility Spectrum Disorders and hypermobile Ehlers-Danlos syndrome.

Collins Hutchinson, Meagan L, Liang, Emily, Fuster, Emily et al.·Autonomic neuroscience : basic & clinical·2025

This study looked at 84 women with connective tissue disorders (HSD/h-EDS) to understand how much autonomic nervous system problems they experience and how these affect their quality of life. The researchers found that these women had severe autonomic symptoms, with nearly 60% also having POTS and about 26% having ME/CFS. Overall, their quality of life was significantly worse than patients with other serious conditions like multiple sclerosis or rheumatoid arthritis.

Autonomic Nervous System
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Assessment of Autonomic Nervous System Function in Patients with Chronic Fatigue Syndrome and Post-COVID-19 Syndrome Presenting with Recurrent Syncope.

Milovanovic, Branislav, Markovic, Nikola, Petrovic, Masa et al.·Journal of clinical medicine·2025

This study examined how the autonomic nervous system (the part that controls heart rate, blood pressure, and other automatic functions) works differently in people with ME/CFS compared to healthy people. Researchers tested 440 people, including those with ME/CFS from unknown causes and those whose ME/CFS developed after COVID-19, using heart and blood pressure monitoring tests. They found that both ME/CFS groups had significant problems with autonomic function and experienced fainting or near-fainting episodes at high rates, though the post-COVID group showed somewhat different patterns.

Autonomic Nervous System
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The Diagnostic Journey of Dysautonomia Patients: Insights from a Patient-Reported Outcome Study.

O'Dell, John A, Walker, Ash, Latham, Andrew J et al.·Journal of patient experience·2025

This study followed 672 adults with dysautonomia (a condition where the nervous system that controls automatic body functions doesn't work properly) to understand how long it takes to get diagnosed and which doctors help with diagnosis. On average, it took 7.7 years for people to receive a diagnosis, and they often saw multiple types of doctors before getting answers. The study found that dysautonomia commonly occurs alongside other conditions like Ehlers-Danlos syndrome, mast cell disorders, and ME/CFS, which can make diagnosis even more confusing.

Autonomic Nervous SystemDiagnostics
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Comprehensive Assessment of Autonomic Nervous System Profiles in Postural Orthostatic Tachycardia Syndrome Among Syncope, Chronic Fatigue, and Post-COVID-19 Patients.

Milovanovic, Branislav, Markovic, Nikola, Petrovic, Masa et al.·Diagnostics (Basel, Switzerland)·2025

This study examined how the nervous system functions differently in people with POTS (a condition causing rapid heart rate when standing) who also have fainting episodes, ME/CFS, or post-COVID illness. Researchers used heart rate monitors, tilt tests, and breathing exercises to measure how well the autonomic nervous system—which controls heart rate and blood pressure—works in each group. They found that POTS appears differently depending on what condition causes it: in syncope patients it involves sympathetic overdrive, while in ME/CFS patients it involves parasympathetic weakness.

Autonomic Nervous System
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Cross-Sectional Study Evaluating the Role of Autonomic Nervous System Functional Diagnostics in Differentiating Post-Infectious Syndromes: Post-COVID Syndrome, Chronic Fatigue Syndrome, and Lyme Disease.

Milovanovic, Branislav, Markovic, Nikola, Petrovic, Masa et al.·Biomedicines·2025

This study compared how the nervous system functions differently in people with Post-COVID syndrome, ME/CFS (both COVID-related and unrelated), and late-stage Lyme disease—three conditions that often feel similar but may have different causes. Researchers tested 758 patients using heart rhythm monitors, tilt tests, and blood pressure measurements to see how their bodies responded to position changes and stress. They found that Lyme disease patients showed a distinct pattern of nerve dysfunction (adrenergic failure), while Post-COVID and ME/CFS patients had different types of nervous system imbalances.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Mismatch between subjective and objective dysautonomia.

Novak, Peter, Systrom, David M, Marciano, Sadie P et al.·Scientific reports·2024

This study examined whether questionnaires that ask patients about autonomic symptoms (like dizziness, heart racing, or sweating problems) match what doctors find when they perform actual autonomic tests. Researchers studied over 2,600 patients and found a surprising disconnect: questionnaires and actual tests did not correlate with each other, meaning some patients reported severe symptoms but tested normally, while others had significant test abnormalities but reported few symptoms. This finding held true across many conditions, including ME/CFS, suggesting that questionnaires alone cannot reliably detect autonomic problems.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Similar Patterns of Dysautonomia in Myalgic Encephalomyelitis/Chronic Fatigue and Post-COVID-19 Syndromes.

Ryabkova, Varvara A, Rubinskiy, Artemiy V, Marchenko, Valeriy N et al.·Pathophysiology : the official journal of the International Society for Pathophysiology·2024

This study found that people with ME/CFS and those with long COVID have similar problems with how their autonomic nervous system (the system that controls heart rate, blood pressure, and other automatic body functions) works. Researchers measured heart rate variability and blood pressure patterns in 34 ME/CFS patients, 29 long COVID patients, and 32 healthy controls. Both patient groups showed reduced autonomic function compared to healthy people, and these problems were linked to their fatigue—but not to depression or anxiety.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Dysautonomia and small fiber neuropathy in post-COVID condition and Chronic Fatigue Syndrome.

Azcue, N, Del Pino, R, Acera, M et al.·Journal of translational medicine·2023

This study compared how the nervous system works differently in people with ME/CFS, people with long COVID, and healthy people. Researchers tested heart rate responses, sweating patterns, and how nerves respond to temperature. They found that people with ME/CFS had more severe problems with heart rate regulation and nerve fiber damage than those with long COVID, and both groups had more problems than healthy controls.

Autonomic Nervous SystemCognitive Impairment
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Cognitive impairment in post-acute sequelae of COVID-19 and short duration myalgic encephalomyelitis patients is mediated by orthostatic hemodynamic changes.

Day, Heather, Yellman, Brayden, Hammer, Sarah et al.·Frontiers in neuroscience·2023

This study examined why people with ME/CFS and long COVID experience 'brain fog' and memory problems. Researchers tested how well people could think and remember before and after standing up quickly (which can make blood pressure drop). They found that people with these illnesses had more trouble thinking clearly after the standing test, and this was linked to unusual changes in their heart rate and blood pressure. The findings suggest that problems with blood flow to the brain during physical stress may be contributing to cognitive difficulties.

Autonomic Nervous SystemCognitive Impairment
E2 ModeratePEM unclearPreliminaryCross-SectionalEditor reviewed

Urine Metabolite Analysis to Identify Pathomechanisms of Long COVID: A Pilot Study.

Taenzer, Maja, Löffler-Ragg, Judith, Schroll, Andrea et al.·International journal of tryptophan research : IJTR·2023

This study examined urine samples from people with Long COVID and ME/CFS to look for chemical imbalances that might explain their symptoms. Researchers found that both groups had lower levels of certain amino acids and neurotransmitters (brain chemicals) compared to healthy people, particularly affecting energy production, mood, and sleep. These chemical signatures could potentially be used as simple urine tests to help doctors understand what is happening in patients and create personalized treatments.

SleepAutonomic Nervous SystemCognitive Impairment
E2 ModeratePEM unclearPreliminaryCase-ControlEditor reviewed

Orthostatic Intolerance in Long-Haul COVID after SARS-CoV-2: A Case-Control Comparison with Post-EBV and Insidious-Onset Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients.

van Campen, C Linda M C, Visser, Frans C·Healthcare (Basel, Switzerland)·2022

This study compared patients with long-haul COVID to two groups of ME/CFS patients (those who got sick after Epstein-Barr virus infection and those who became ill gradually) to understand a common symptom called orthostatic intolerance—dizziness or fainting when standing up. Researchers found that long-haul COVID patients had similar symptoms and physical responses to standing as ME/CFS patients, and all three groups showed comparable problems with blood flow and heart function during the standing test. The findings suggest that long-haul COVID and ME/CFS may be essentially the same underlying condition.

Autonomic Nervous System
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Orthostatic Challenge Causes Distinctive Symptomatic, Hemodynamic and Cognitive Responses in Long COVID and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Vernon, Suzanne D, Funk, Sherlyn, Bateman, Lucinda et al.·Frontiers in medicine·2022

Researchers tested whether a simple 10-minute standing test (NASA Lean Test) could reveal problems in people with Long COVID and ME/CFS. The test made symptoms worse in both patient groups but not in healthy people, and caused measurable changes in blood pressure and thinking speed. This suggests the test could help doctors confirm what patients are experiencing and provide objective evidence of their condition.

Autonomic Nervous SystemDiagnosticsCognitive Impairment
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An online survey of pelvic congestion support group members regarding comorbid symptoms and syndromes.

Smith, Steven J, Sichlau, Michael, Sewall, Luke E et al.·Phlebology·2022

This study surveyed women with pelvic congestion syndrome (a vascular condition affecting pelvic blood vessels) to see how often they also experience other medical conditions like chronic fatigue, fibromyalgia, and irritable bowel syndrome. Researchers found that these co-occurring conditions were much more common in this group than in the general population, suggesting that these conditions may be connected in ways we don't yet understand.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Orthostatic Symptoms and Reductions in Cerebral Blood Flow in Long-Haul COVID-19 Patients: Similarities with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Campen, C Linda M C van, Rowe, Peter C, Visser, Frans C·Medicina (Kaunas, Lithuania)·2021

This study compared people with long-haul COVID-19 to people with ME/CFS to see if they experience similar problems with dizziness and blood flow when standing up. Researchers found that long-haul COVID patients had very similar symptoms to ME/CFS patients and showed even greater reductions in blood flow to the brain during tilt testing. The findings suggest that COVID-19 infection may trigger ME/CFS-like illness in some people.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Postural orthostatic tachycardia syndrome in patients of orthostatic intolerance symptoms: an ambispective study.

Chouksey, Dinesh, Rathi, Pankaj, Sodani, Ajoy et al.·AIMS neuroscience·2021

This study looked at patients who experience dizziness, fainting, or heart racing when standing up—symptoms of a condition called POTS (Postural Orthostatic Tachycardia Syndrome). Researchers tested 246 patients with these symptoms and confirmed POTS in 40 of them using a special tilt-table test. Most POTS patients experienced fainting, lightheadedness, and heart palpitations, and nearly half also had a related condition causing fainting.

Autonomic Nervous System
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Functional gastrointestinal disorders are increased in joint hypermobility-related disorders with concomitant postural orthostatic tachycardia syndrome.

Tai, Foong Way David, Palsson, Olafur S, Lam, Ching Y et al.·Neurogastroenterology and motility·2020

This study looked at people with joint hypermobility disorders (including Ehlers-Danlos syndrome) to understand how often they experience stomach and digestive problems. The researchers found that those who also have POTS (a condition affecting heart rate and blood pressure when standing) had significantly more digestive issues than those without POTS. The digestive problems remained worse in the POTS group even after accounting for other conditions like chronic fatigue syndrome.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Urodynamic characteristics might be variable in bladder pain syndrome/interstitial cystitis patients with different non-bladder co-morbid conditions.

Cheng, Wei-Ming, Fan, Yu-Hua, Lin, Alex T L·Journal of the Chinese Medical Association : JCMA·2018

This study looked at how other health conditions that often occur alongside bladder pain syndrome (interstitial cystitis) might affect bladder function. Researchers tested 111 patients with bladder pain and found that 78% also had at least one other condition, such as irritable bowel syndrome, fibromyalgia, or chronic fatigue syndrome. They discovered that patients with both bladder pain and irritable bowel syndrome had different bladder function patterns than those with bladder pain alone.

Autonomic Nervous System
E2 ModeratePEM not requiredWeak / uncertainCross-SectionalEditor reviewed

Negative Affectivity, Depression, and Resting Heart Rate Variability (HRV) as Possible Moderators of Endogenous Pain Modulation in Functional Somatic Syndromes.

Van Den Houte, Maaike, Van Oudenhove, Lukas, Van Diest, Ilse et al.·Frontiers in psychology·2018

This study looked at how the body's natural pain-blocking system works in people with fibromyalgia and chronic fatigue syndrome (CFS), and whether mood, depression, or heart rate variability might affect this system. Researchers compared 78 patients with these conditions to 33 healthy people using a test where they applied cold and electrical stimuli to see if pain would decrease. Unfortunately, the main pain-blocking effect the researchers expected to find did not appear in either group, so they could not draw clear conclusions about what affects pain modulation.

Pain and SensitizationAutonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Painful temporomandibular disorders are common in patients with postural orthostatic tachycardia syndrome and impact significantly upon quality of life.

Durham, Justin, McDonald, Claire, Hutchinson, Luke et al.·Journal of oral & facial pain and headache·2015

This study found that people with PoTS (a condition causing rapid heart rate when standing) often also have painful jaw disorders (TMD). Nearly half of the patients studied screened positive for TMD, and those with TMD reported that it significantly worsened their quality of life. The researchers suggest that doctors should routinely check for jaw pain in PoTS patients.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

[Impact of the fibromyalgia in the chronic fatigue syndrome].

Faro, Mónica, Sáez-Francàs, Naia, Castro-Marrero, Jesús et al.·Medicina clinica·2014

This study looked at nearly 1,000 ME/CFS patients to see how many also had fibromyalgia (a condition causing widespread pain and fatigue), and whether having both conditions made symptoms worse. They found that about half of the ME/CFS patients also had fibromyalgia, and those patients experienced higher levels of fatigue, pain, sleep problems, and cognitive difficulties. People with both conditions reported a much greater impact on their quality of life compared to those with ME/CFS alone.

SleepAutonomic Nervous SystemCognitive Impairment
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

High flow variant postural orthostatic tachycardia syndrome amplifies the cardiac output response to exercise in adolescents.

Pianosi, Paolo T, Goodloe, Adele H, Soma, David et al.·Physiological reports·2014

This study found that about 40% of adolescents with POTS (a condition causing dizziness, fatigue, and rapid heartbeat when standing) have an unusual heart response to exercise: their hearts pump out more blood than expected to keep blood pressure normal. Instead of blood vessels tightening during exercise as they normally do, these patients' blood vessels stay too relaxed, forcing the heart to work harder by pumping more blood to maintain adequate pressure.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Comorbidity of postural orthostatic tachycardia syndrome and chronic fatigue syndrome in an Australian cohort.

Reynolds, G K, Lewis, D P, Richardson, A M et al.·Journal of internal medicine·2014

This study looked at patients with ME/CFS to see how many also have POTS (a condition where heart rate increases too much when standing). The researchers found that about 1 in 9 ME/CFS patients also had POTS, and these patients were younger, got sick more recently, and found it much harder to stand for long periods compared to ME/CFS patients without POTS.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCase-ControlEditor reviewed

Bladder pain syndrome/interstitial cystitis is associated with hyperthyroidism.

Chung, Shiu-Dong, Liu, Shih-Ping, Lin, Ching-Chun et al.·PloS one·2013

This study found that women with bladder pain syndrome/interstitial cystitis (BPS/IC) are more than twice as likely to have had hyperthyroidism (an overactive thyroid) compared to women without bladder pain. The researchers reviewed medical records from Taiwan and suggest that doctors treating women with thyroid problems should ask about urinary symptoms.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Neurohumoral and haemodynamic profile in postural tachycardia and chronic fatigue syndromes.

Okamoto, Luis E, Raj, Satish R, Peltier, Amanda et al.·Clinical science (London, England : 1979)·2012

This study looked at patients with POTS (a condition where heart rate increases too much when standing) to see how many also have ME/CFS and whether they are different from POTS patients without ME/CFS. The researchers found that most POTS patients experience severe fatigue, and about two-thirds also meet ME/CFS criteria. Those with both conditions had stronger heart rate increases when standing and signs of greater stress hormone activity.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Comorbid health conditions in women with syncope.

Ulas, Umit H, Chelimsky, Thomas C, Chelimsky, Gisela et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2010

This study looked at hospital records of over 305,000 patients admitted for fainting (syncope) to see which health conditions were more common in women versus men. Researchers found that women were more likely to have several conditions related to nervous system problems that control blood pressure and heart rate, including chronic fatigue syndrome, migraines, and postural tachycardia syndrome (a condition where heart rate increases abnormally when standing). These autonomic conditions were especially common in women of reproductive age.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

A comparison of dysautonomias comorbid with cyclic vomiting syndrome and with migraine.

Chelimsky, Gisela, Madan, Shruti, Alshekhlee, Amer et al.·Gastroenterology research and practice·2009

This study compared people with cyclic vomiting syndrome (CVS) to people with migraine headaches to see if they have the same associated conditions. Researchers looked at 21 CVS patients, 46 migraine patients, and 36 healthy controls, testing for 12 different conditions including orthostatic intolerance (feeling dizzy when standing), fibromyalgia, and chronic fatigue. While CVS and migraine shared many of the same comorbidities, CVS patients had significantly more cases of complex regional pain syndrome, suggesting these conditions may not be as similar as previously thought.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCross-SectionalEditor reviewed

Electrocardiographic QT interval and cardiovascular reactivity in fibromyalgia differ from chronic fatigue syndrome.

Naschitz, Jochanan E, Slobodin, Gleb, Sharif, Dauod et al.·European journal of internal medicine·2008

This study found that ME/CFS and fibromyalgia, two conditions that seem similar on the surface, actually show different patterns on heart tests. People with ME/CFS had shorter QT intervals on their electrocardiogram (a measure of heart electrical activity) and had more dramatic blood pressure and heart rate changes during a tilting test compared to people with fibromyalgia. These differences suggest the two conditions may be distinct disorders rather than variants of the same illness.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Patterns of hypocapnia on tilt in patients with fibromyalgia, chronic fatigue syndrome, nonspecific dizziness, and neurally mediated syncope.

Naschitz, Jochanan E, Mussafia-Priselac, Renata, Kovalev, Yulia et al.·The American journal of the medical sciences·2006

This study looked at whether people with ME/CFS, fibromyalgia, and dizziness breathe too fast when standing up, causing them to exhale too much carbon dioxide (a condition called hypocapnia). Researchers tested 585 people using a tilt table that slowly raises the upper body while measuring breathing patterns. They found that 9-27% of people with these conditions showed abnormal breathing on the tilt test, compared to 0-2% of healthy controls, suggesting this may be a real but not universal feature of these illnesses.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Hyperventilation and amplified blood pressure response: is there a link?

Naschitz, J E, Mussafia-Priselac, R, Peck, E R et al.·Journal of human hypertension·2005

This study looked at whether rapid, shallow breathing (hyperventilation) causes blood pressure to rise when people change position, such as standing up. Researchers tested 320 patients with various conditions including ME/CFS using a tilt table test while measuring breathing CO2 levels. They found that hyperventilation during the test did not lead to higher blood pressure increases, suggesting that rapid breathing may not be the cause of blood pressure problems in these patient groups.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Cardiovascular reactivity in fibromyalgia: evidence for pathogenic heterogeneity.

Naschitz, Jochanan E, Rozenbaum, Michael, Fields, Madeline C et al.·The Journal of rheumatology·2005

This study looked at how the hearts of fibromyalgia patients respond to position changes (lying down versus standing up) compared to people with other conditions including ME/CFS. Researchers used a specialized test that measures heart rate patterns during a tilt test and analyzed the data with advanced mathematical methods. They found no single heart response pattern that was unique to fibromyalgia, suggesting that fibromyalgia patients have different types of heart responses rather than one shared pattern.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Early life stress, negative paternal relationships, and chemical intolerance in middle-aged women: support for a neural sensitization model.

Bell, I R, Baldwin, C M, Russek, L G et al.·Journal of women's health·1998

This study looked at whether women with chemical sensitivity (difficulty tolerating everyday chemicals) had experienced more childhood stress or difficult relationships with their fathers compared to women with depression alone or women without these conditions. The researchers found that women with chemical sensitivity had weaker relationships with their fathers and showed signs of nervous system overactivity. The study suggests that repeated exposure to stress early in life might train the nervous system to react more strongly to chemicals and other triggers.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceObservationalEditor reviewed

Autonomic Dysfunction in Patients with Acute Infection with Coxiella burnetii.

Milovanović, Branislav, Marković, Nikola, Ristanović, Elizabeta et al.·Pathogens (Basel, Switzerland)·2025

This study looked at how the autonomic nervous system (the part that controls heart rate, blood pressure, and other automatic body functions) works in people who had acute infection with Coxiella burnetii, a bacterium that causes Q fever. Researchers tested 100 infected patients and 56 healthy controls using heart monitoring tests and found that infected patients had more problems with autonomic control, particularly in how their bodies regulate heart rate and blood pressure. These findings suggest that this infection might trigger lasting problems with the autonomic nervous system that could contribute to ME/CFS symptoms.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceLongitudinalEditor reviewed

Fatigue in Epstein-Barr virus infected adolescents and healthy controls: A prospective multifactorial association study.

Pedersen, Maria, Asprusten, Tarjei Tørre, Godang, Kristin et al.·Journal of psychosomatic research·2019

This study followed teenagers with acute Epstein-Barr virus (EBV) infection and compared them to healthy teenagers to understand what causes fatigue. Researchers measured 148 different factors including symptoms, quality of life, sleep, emotions, immune markers, and heart rate control at the start of infection and again six months later. They found that fatigue was consistently linked to sleep problems, negative emotions, and poor quality of life, but surprisingly, markers of active infection were not associated with how tired people felt.

SleepAutonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceObservationalEditor reviewed

Predictors of Post-Infectious Chronic Fatigue Syndrome in Adolescents.

Jason, Leonard A, Katz, Ben Z, Shiraishi, Yukiko et al.·Health psychology and behavioral medicine·2014

This study followed over 300 teenagers who had infectious mononucleosis to see which ones developed ME/CFS afterward. Researchers measured various factors at baseline, including how tired the teens felt, how many days they spent in bed, stress levels, and mood. The key finding was that the severity of the initial mono illness—particularly how long teens stayed in bed—was the strongest predictor of who would develop ME/CFS within 6 months.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceLongitudinalEditor reviewed

Orthostatic tolerance testing in a prospective cohort of adolescents with chronic fatigue syndrome and recovered controls following infectious mononucleosis.

Katz, Ben Z, Stewart, Julian M, Shiraishi, Yukiko et al.·Clinical pediatrics·2012

This study looked at whether teenagers with ME/CFS have trouble standing up for long periods (a condition called orthostatic intolerance). Researchers tested 36 teens with ME/CFS and 43 recovered teens, all about 6 months after having infectious mononucleosis. Surprisingly, they found that similar numbers of both groups had difficulty with standing tolerance, suggesting this may not be a key difference between those who recover and those who develop ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Comparing autonomic nervous system function in patients with functional somatic syndromes, stress-related syndromes and healthy controls.

Van Den Houte, Maaike, Ramakers, Indra, Van Oudenhove, Lukas et al.·Journal of psychosomatic research·2025

This study measured how the nervous system responds to stress in people with ME/CFS and similar conditions, compared to healthy people. Researchers found that patients with ME/CFS and stress-related conditions had their 'stress response system' stuck in overdrive even at rest, and this system didn't properly calm down after stress passed. These findings suggest that autonomic nervous system dysfunction—an imbalance in the automatic systems that control heart rate and other vital functions—may be a common feature across these conditions.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Development and Validation of the Short Form (JAEN-10) of the Joint Assessment of Equilibrium and Neuromotor Status Scale (JAEN-20).

Peinado-Rubia, Ana Belén, Osuna-Pérez, María Catalina, Núñez-Fuentes, David et al.·Journal of functional morphology and kinesiology·2024

Researchers created a shorter version of a balance and movement test (JAEN-10) to measure physical problems in people with fibromyalgia. The new 10-question test works just as well as the original 20-question version but takes less time to complete, which is helpful for people who get tired easily. The test successfully identified people with fibromyalgia and those at risk of falling.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Poor health-related quality of life in postural orthostatic tachycardia syndrome in comparison with a sex- and age-matched normative population.

Seeley, Marie-Claire, Gallagher, Celine, Ong, Eric et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2023

This study compared quality of life in people with POTS (a condition causing rapid heartbeat when standing) to people without POTS. Researchers found that people with POTS reported significantly worse quality of life across all areas tested, including mobility, self-care, daily activities, pain, and mood. The impact was consistent across all age groups, and was worse in people with severe symptoms, women, those with fatigue, and those who also had ME/CFS.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

End-Tidal CO2 in Patients with Panic Disorder, Stress-Related or Functional Syndromes, Versus Healthy Controls.

Ramakers, Indra, Van Den Houte, Maaike, Van Oudenhove, Lukas et al.·Applied psychophysiology and biofeedback·2023

This study looked at how people with ME/CFS, fibromyalgia, burnout, and panic disorder breathe differently compared to healthy people. Researchers measured carbon dioxide levels in participants' breath while they rested and during a breathing challenge. They found that people with chronic conditions like ME/CFS showed less active stress responses in their breathing, while those with acute stress conditions showed overactive breathing patterns.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryObservationalEditor reviewed

Evaluation of Fatigue in Cancer Patients in An Area Affected by The Great East Japan Earthquake.

Sato, Daisuke·Asia-Pacific journal of oncology nursing·2020

This study looked at fatigue in cancer patients receiving chemotherapy who lived in an area affected by a major earthquake in Japan. Researchers measured both what patients reported about their tiredness and objective measurements of nervous system function and activity levels. The main finding was that patients showed changes in how their nervous system was functioning, with their stress-response system becoming more dominant over time.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceObservationalEditor reviewed

Association between quadrivalent human papillomavirus vaccination and selected syndromes with autonomic dysfunction in Danish females: population based, self-controlled, case series analysis.

Hviid, Anders, Thorsen, Nicklas M, Valentiner-Branth, Palle et al.·BMJ (Clinical research ed.)·2020

This study examined whether the HPV vaccine (used to prevent cervical cancer) was linked to ME/CFS, complex regional pain syndrome, or POTS in over 1.3 million Danish girls and women. Researchers found no evidence that the vaccine caused these conditions—the rates of these illnesses were similar whether or not girls received the vaccine.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceObservationalEditor reviewed

A cluster analysis of serious adverse event reports after human papillomavirus (HPV) vaccination in Danish girls and young women, September 2009 to August 2017.

Ward, Daniel, Thorsen, Nicklas Myrthue, Frisch, Morten et al.·Euro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin·2019

This study examined adverse event reports submitted to Danish health authorities after HPV vaccination between 2009 and 2017. Researchers found that fatigue, dizziness, and headache were common symptoms reported, and noticed that some clusters of reports—particularly those mentioning cognitive problems and sleep issues—were submitted during periods of increased media coverage about vaccine safety concerns.

Autonomic Nervous SystemCognitive Impairment
E2 ModeratePEM unclearPreliminaryObservationalEditor reviewed

Verification of exercise-induced transient postural tachycardia phenotype in Gulf War Illness.

Garner, Richard S, Rayhan, Rakib U, Baraniuk, James N·American journal of translational research·2018

Researchers found that about one-fourth of Gulf War Illness patients developed an unusual heart rate response after exercise: their heart raced when they stood up, even though this didn't happen before exercise. This temporary condition, called the START phenotype, appeared around 2 hours after exercise and was different from a similar condition called POTS that some patients had continuously. This discovery suggests that exercise can trigger a specific cardiovascular problem in some Gulf War Illness patients.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Postural tachycardia syndrome is associated with significant symptoms and functional impairment predominantly affecting young women: a UK perspective.

McDonald, Claire, Koshi, Sharon, Busner, Lorna et al.·BMJ open·2014

This study looked at 136 people in the UK with postural tachycardia syndrome (PoTS)—a condition where your heart rate increases too much when you stand up—and found that it causes serious tiredness and functional problems, especially in young women. The researchers compared two groups of PoTS patients and found their symptoms and quality-of-life impacts were similar to those in people with chronic fatigue syndrome (ME/CFS). Importantly, there was no consistent treatment approach across patients, with some taking no medication and others on different drug combinations.

Autonomic Nervous SystemCognitive Impairment
E2 ModeratePEM not requiredModerate confidenceCase-ControlEditor reviewed

Chronic fatigue in adult survivors of childhood cancer: associated symptoms, neuroendocrine markers, and autonomic cardiovascular responses.

Zeller, Bernward, Ruud, Ellen, Havard Loge, Jon et al.·Psychosomatics·2014

This study looked at cancer survivors who experience chronic fatigue and compared them to survivors without fatigue. Researchers measured symptoms, stress hormones, and how the body responds to position changes. People with chronic fatigue reported more pain, confusion, and symptoms like heart palpitations and temperature sensitivity, though their heart responses to standing were similar to those without fatigue.

Autonomic Nervous System
E2 ModeratePEM not requiredPreliminaryCross-SectionalEditor reviewed

Autonomic instability, as measured by pupillary unrest, is not associated with multiple sclerosis fatigue severity.

Egg, R, Högl, B, Glatzl, S et al.·Multiple sclerosis (Houndmills, Basingstoke, England)·2002

This study looked at whether problems with the nervous system's ability to regulate automatic body functions (like pupil responses) might explain fatigue in multiple sclerosis patients. Researchers measured pupil movements in MS patients and healthy volunteers, then compared these measurements to fatigue severity scores. Surprisingly, they found the opposite of what they expected: people with more pupil instability actually reported less fatigue, not more.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

Cardiovascular response to upright tilt in fibromyalgia differs from that in chronic fatigue syndrome.

Naschitz, J E, Rozenbaum, M, Rosner, I et al.·The Journal of rheumatology·2001

This study compared how the bodies of people with fibromyalgia and ME/CFS respond to standing up from lying down. Researchers measured blood pressure and heart rate while patients lay down and then tilted upright for 30 minutes. They found that fibromyalgia and ME/CFS patients had very different cardiovascular responses to this position change, suggesting these are two distinct conditions rather than the same illness.

Autonomic Nervous System
E2 ModeratePEM not requiredModerate confidenceCross-SectionalEditor reviewed

The role of delayed orthostatic hypotension in the pathogenesis of chronic fatigue.

Streeten, D H, Anderson, G H·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·1998

This study looked at whether problems with blood pressure regulation—specifically a delayed drop in blood pressure when standing up—might explain why some people with chronic fatigue syndrome feel so exhausted. Researchers surveyed 431 patients with various neurological and hormonal disorders and found that fatigue was very common in people with delayed blood pressure drops and low cortisol levels (70-83%), but much less common in people with other conditions like multiple system atrophy (7-33%). This suggests a possible connection between blood pressure regulation problems and severe fatigue.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryCase-ControlEditor reviewed

Improvement in Upper Limb and Systemic Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) Symptoms After Surgical Treatment of Neurogenic Thoracic Outlet Syndrome.

Christoforou, Maritsa E, Lum, Ying Wei, Sroge, Sally C et al.·Cureus·2025

This case study describes a 19-year-old woman with ME/CFS who also had a condition called thoracic outlet syndrome (TOS), where nerves in the upper chest become compressed. After surgery to relieve this compression on both sides of her body, she experienced not only relief from arm numbness and tingling, but also surprising improvements in migraines, brain fog, dizziness, and vision problems. This suggests that some ME/CFS patients might benefit from being evaluated for TOS, as treating it could potentially help with multiple symptoms.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM unclearPreliminaryObservationalEditor reviewed

Effects of recumbent isometric yoga on the orthostatic cardiovascular response of patients with myalgic encephalomyelitis/chronic fatigue syndrome.

Oka, Takakazu, Lkhagvasuren, Battuvshin·BioPsychoSocial medicine·2025

This small study looked at whether a gentle yoga practice done while lying down could help ME/CFS patients who experience dizziness or fast heartbeats when standing up (a condition called POTS). Ten women with ME/CFS practiced this special yoga for 12 weeks, and the researchers measured their blood pressure and heart rate before and after standing. The two patients who had POTS at the start showed improvement and had normal responses after the yoga practice.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryCase-ControlEditor reviewed

Beneficial effects of intermittent intravenous saline infusion in dysautonomic patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: a case-series.

Sjögren, Per, Huhmar, Helena, Bertilson, Bo C et al.·Frontiers in neurology·2025

This small study tested whether giving patients with ME/CFS regular salt water infusions through an IV could help with symptoms like dizziness and rapid heartbeat when standing up. Twenty-two patients received these infusions every three weeks for 9 weeks, and most reported feeling better, with improvements in symptom scores, quality of life, and ability to work. While the results were encouraging, this was a preliminary study without a control group, so more research is needed to confirm whether this treatment actually works.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryEditor reviewed

Static and Kinetic Disequilibrium are Central Neural Signs in Patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome-Therapeutic Effect of Repetitive Transcranial Magnetic Stimulation.

Miwa, Kunihisa·Journal of integrative neuroscience·2025

This study found that nearly half of ME/CFS patients experience balance problems—either when standing still (static disequilibrium) or when walking (kinetic disequilibrium). These balance issues were linked to difficulty standing upright and limitations in daily activities. When researchers used a brain stimulation treatment called repetitive transcranial magnetic stimulation (rTMS) on specific brain regions, most patients' balance problems improved, suggesting the root cause is in the central nervous system rather than the inner ear alone.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryEditor reviewed

Stress-Related Chronic Fatigue Syndrome: A Case Report with a Positive Response to Alpha-Methyl-P-Tyrosine (AMPT) Treatment.

Ljungström, Maria, Oltra, Elisa, Pardo, Marta·International journal of molecular sciences·2024

This case report describes one patient with ME/CFS who had high levels of stress and an overactive stress-response system in his body. He was treated with a medication called alpha-methyl-p-tyrosine (AMPT), which lowers stress chemicals in the body, and his symptoms improved. The report suggests that some people with ME/CFS may have problems with how their body produces and manages stress chemicals, and this medication might help them.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryLongitudinalEditor reviewed

Time-dependent complexity characterisation of activity patterns in patients with Chronic Fatigue Syndrome.

Rabaey, Paloma, Decat, Peter, Heytens, Stefan et al.·BioPsychoSocial medicine·2024

Researchers tracked the physical activity patterns of 7 ME/CFS patients over 3 weeks to see if the complexity of how they move changes over time and relates to how well they're functioning. They found that each patient's activity complexity varied significantly from week to week, and these changes didn't consistently match whether patients reported feeling better or worse. This suggests that measuring activity patterns alone may not be a reliable way to track how ME/CFS patients are doing.

Autonomic Nervous System
E3 PreliminaryPEM requiredPreliminaryEditorialEditor reviewed

Post-exertional malaise in daily life and experimental exercise models in patients with myalgic encephalomyelitis/chronic fatigue syndrome.

Vøllestad, Nina K, Mengshoel, Anne Marit·Frontiers in physiology·2023

This paper reviews how post-exertional malaise (PEM)—the worsening of symptoms after physical or mental activity—is experienced and studied in ME/CFS patients. Patients describe PEM in many different ways and report that it can start immediately or be delayed by days, lasting anywhere from a few days to months. When researchers use standardized exercise tests in laboratories, they see more immediate symptom worsening, but the duration still varies widely between patients.

Autonomic Nervous SystemPost-Exertional Malaise
E3 PreliminaryPEM unclearPreliminaryCase-ControlEditor reviewed

Case report: Recurrent cervical spinal stenosis masquerading as myalgic encephalomyelitis/chronic fatigue syndrome with orthostatic intolerance.

Edwards, Charles C, Edwards, Charles C, Heinlein, Scott et al.·Frontiers in neurology·2023

This case report describes a woman who was thought to have ME/CFS and experienced symptoms of dizziness upon standing (orthostatic intolerance). Doctors discovered she actually had cervical spinal stenosis—a narrowing of the spinal canal in her neck that was compressing her spinal cord. After surgery to relieve the compression, her ME/CFS and orthostatic intolerance symptoms improved significantly. Years later, her symptoms returned because the surgical implant shifted, compressing the spinal cord again. A second surgery provided similar improvement, suggesting that spinal stenosis may have been causing or worsening her ME/CFS symptoms rather than the other way around.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryCase-ControlEditor reviewed

Orthostatic intolerance as a potential contributor to prolonged fatigue and inconsistent performance in elite swimmers.

Petracek, Lindsay S, Eastin, Ella F, Rowe, Ian R et al.·BMC sports science, medicine & rehabilitation·2022

This study looked at five elite swimmers who experienced severe fatigue and couldn't perform at their usual level. The researchers tested whether orthostatic intolerance—a condition where the body struggles to maintain proper blood pressure when standing—might explain their symptoms. When the swimmers were tested with standing or tilt table tests, they all felt fatigued and other symptoms appeared. After receiving treatment with extra salt and fluids, all five swimmers felt significantly better and returned to normal performance.

Autonomic Nervous System
E3 PreliminaryPEM not requiredModerate confidenceEditor reviewed

Deconditioning does not explain orthostatic intolerance in ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome).

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Journal of translational medicine·2021

This study examined whether being physically deconditioned (out of shape) causes the dizziness and fainting symptoms that many ME/CFS patients experience when standing up. Researchers tested 199 ME/CFS patients and 22 healthy people using exercise tests and a tilt table test that measures blood flow to the brain. The results showed that ME/CFS patients had significant problems with blood flow to their brain when tilted upright, but this problem occurred regardless of how deconditioned they were.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryMechanisticEditor reviewed

Homeostatic disturbance of thermoregulatory functions in rats with chronic fatigue.

Li, Danxi, Hu, Di, Shigeta, Mika et al.·Neuroscience research·2021

Many ME/CFS patients report feeling feverish or chilled even when their body temperature is normal. This study used rats with chronic fatigue to understand what goes wrong with the body's temperature control system. Researchers found that in early fatigue, the body tried to raise its temperature to cope, but over time this system broke down and stopped working properly, which may explain why fatigue becomes long-lasting.

Autonomic Nervous System
E3 PreliminaryPEM unclearModerate confidenceCross-SectionalEditor reviewed

Orthostatic stress testing in myalgic encephalomyelitis/chronic fatigue syndrome patients with or without concomitant fibromyalgia: effects on pressure pain thresholds and temporal summation.

van Campen, C Linda M C, Rowe, Peter C, Verheugt, Freek W A et al.·Clinical and experimental rheumatology·2021

This study tested how standing up quickly (which can trigger ME/CFS symptoms) affects pain sensitivity in ME/CFS patients. Researchers measured how much pressure patients could tolerate on their finger and shoulder before and after a tilt test. They found that ME/CFS patients became more pain-sensitive after the tilt test, meaning their bodies responded to pain more strongly than healthy people, and this effect was even more pronounced in those who also had fibromyalgia.

Pain and SensitizationAutonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryObservationalEditor reviewed

Changes in the Allostatic Response to Whole-Body Cryotherapy and Static-Stretching Exercises in Chronic Fatigue Syndrome Patients vs. Healthy Individuals.

Kujawski, Sławomir, Bach, Anna M, Słomko, Joanna et al.·Journal of clinical medicine·2021

This study compared how the bodies of ME/CFS patients and healthy people respond to cold therapy combined with stretching exercises. Researchers measured fatigue, thinking ability, heart function, and nervous system activity before and after 10 sessions of treatment. They found that ME/CFS patients showed more disrupted connections between these body systems compared to healthy controls, suggesting their bodies struggle more to maintain balance under stress.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Mitochondria and immunity in chronic fatigue syndrome.

Anderson, G, Maes, M·Progress in neuro-psychopharmacology & biological psychiatry·2020

This review examines how problems with energy-producing structures in cells (mitochondria) and immune system dysfunction may contribute to ME/CFS. The authors propose that two key areas—the gut and immune cells—work together with the body's natural sleep-wake cycle to drive the condition. They also explore how factors like viral infections, gut bacteria, and hormones may play interconnected roles in ME/CFS symptoms.

Autonomic Nervous SystemImmune System
E3 PreliminaryPEM unclearPreliminaryCross-SectionalEditor reviewed

Cerebral Blood Flow Is Reduced in Severe Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients During Mild Orthostatic Stress Testing: An Exploratory Study at 20 Degrees of Head-Up Tilt Testing.

van Campen, C Linda M C, Rowe, Peter C, Visser, Frans C·Healthcare (Basel, Switzerland)·2020

This study looked at blood flow to the brain in 19 people with severe ME/CFS who have difficulty standing up (orthostatic intolerance). When patients tilted their heads up at a mild 20-degree angle for 15 minutes, blood flow to their brains dropped by an average of 27%. All 19 patients showed this abnormal reduction in brain blood flow, suggesting this shorter, gentler test could help diagnose the condition even in the most severely ill patients who cannot tolerate longer or more intense tests.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryEditor reviewed

A Unifying Hypothesis of the Pathophysiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): Recognitions from the finding of autoantibodies against ß2-adrenergic receptors.

Wirth, Klaus, Scheibenbogen, Carmen·Autoimmunity reviews·2020

Researchers found that some ME/CFS patients have antibodies (immune proteins) that attack receptors that normally help blood vessels relax and improve blood flow. When these receptors don't work properly, blood vessels may constrict and reduce oxygen delivery to muscles and the brain. This could explain why ME/CFS patients experience fatigue, pain, and cognitive problems.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Sympathetic neural hyperalgesia edema syndrome as a cause of autoimmune hearing loss.

Check, J H·Clinical and experimental obstetrics & gynecology·2017

This case study describes one woman with ME/CFS, pelvic pain, and diarrhea who was given the stimulant medication dextroamphetamine to help with fertility. Unexpectedly, not only did her ME/CFS symptoms improve, but her hearing loss—which had not responded to months of steroid treatment—also significantly improved, as confirmed by hearing tests.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryMechanisticEditor reviewed

Phenylephrine alteration of cerebral blood flow during orthostasis: effect on n-back performance in chronic fatigue syndrome.

Medow, Marvin S, Sood, Shilpa, Messer, Zachary et al.·Journal of applied physiology (Bethesda, Md. : 1985)·2014

Many ME/CFS patients experience dizziness and cognitive problems when standing up because blood flow to the brain decreases. This study tested whether a medication called phenylephrine, which raises blood pressure, could help restore brain blood flow and improve thinking tasks during standing. The researchers found that phenylephrine reduced the brain blood flow drop and helped ME/CFS patients perform better on memory tests while upright.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

Orthostatic responses in adolescent chronic fatigue syndrome: contributions from expectancies as well as gravity.

Wyller, Vegard Bruun, Fagermoen, Even, Sulheim, Dag et al.·BioPsychoSocial medicine·2014

When people with ME/CFS stand up or imagine standing, their body's nervous system responds differently than in healthy people. This study found that teenagers with ME/CFS have higher resting heart rate and blood pressure, and their nervous system shows stronger stress responses when they think about standing upright, even though their actual physical response to tilting was similar to healthy peers. This suggests that both the physical challenge of gravity and a person's expectations or anxiety about standing may contribute to the symptoms they experience.

Autonomic Nervous System
E3 PreliminaryPEM requiredPreliminaryReview-NarrativeEditor reviewed

A neuro-immune model of Myalgic Encephalomyelitis/Chronic fatigue syndrome.

Morris, Gerwyn, Maes, Michael·Metabolic brain disease·2013

This study proposes a theory about how ME/CFS develops and persists. The researchers suggest that an initial infection triggers the immune system, which then gets stuck in an overactive state even after the infection is cleared. This causes ongoing inflammation, energy problems in cells, and damage to the nervous system, leading to the characteristic symptoms including post-exertional malaise (feeling worse after activity).

NeuroinflammationAutonomic Nervous SystemImmune SystemPost-Exertional Malaise
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

Norepinephrine and epinephrine responses to physiological and pharmacological stimulation in chronic fatigue syndrome.

Strahler, Jana, Fischer, Susanne, Nater, Urs M et al.·Biological psychology·2013

This study looked at how the body's stress hormones (norepinephrine and epinephrine) respond in ME/CFS patients compared to healthy people. Researchers tested 21 ME/CFS patients and 20 controls using exercise and a hormone-stimulation test, measuring stress hormones before and after. ME/CFS patients showed weaker hormone responses to exercise, particularly lower baseline levels and blunted epinephrine release, which could help explain why physical activity feels so exhausting.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Caught in the thickness of brain fog: exploring the cognitive symptoms of Chronic Fatigue Syndrome.

Ocon, Anthony J·Frontiers in physiology·2013

ME/CFS causes cognitive difficulties that patients often describe as "brain fog"—a feeling of foggy thinking, slow mental processing, and trouble concentrating. This review suggests brain fog may result from reduced blood flow to the brain combined with the physical stress of standing (which worsens symptoms in many patients), plus the extra mental effort required to complete tasks. Understanding these overlapping factors could help explain why cognitive symptoms feel so exhausting.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Brain dysfunction as one cause of CFS symptoms including difficulty with attention and concentration.

Natelson, Benjamin H·Frontiers in physiology·2013

This study suggests that ME/CFS is not one single disease but rather multiple conditions with different underlying causes. By grouping patients based on specific characteristics—like whether they have psychiatric diagnoses, fibromyalgia, or blood pressure problems when standing—researchers found that different groups showed different types of brain dysfunction. This approach could help explain why some patients experience trouble with concentration and attention in different ways.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM not requiredPreliminaryMechanisticEditor reviewed

Modulation of the axon-reflex response to local heat by reactive oxygen species in subjects with chronic fatigue syndrome.

Medow, Marvin S, Aggarwal, Arun, Baugham, Ila et al.·Journal of applied physiology (Bethesda, Md. : 1985)·2013

When skin is heated, blood vessels normally dilate to increase blood flow. This study found that people with ME/CFS have lower baseline blood flow in their skin compared to healthy people. When researchers used drugs to reduce harmful molecules called reactive oxygen species (particularly hydrogen peroxide), blood flow improved and the initial blood vessel response to heat increased in ME/CFS patients but not in healthy controls.

Pain and SensitizationAutonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

Postural neurocognitive and neuronal activated cerebral blood flow deficits in young chronic fatigue syndrome patients with postural tachycardia syndrome.

Stewart, Julian M, Medow, Marvin S, Messer, Zachary R et al.·American journal of physiology. Heart and circulatory physiology·2012

When people with ME/CFS try to stand upright or tilt backward, their brain doesn't get enough blood flow to think clearly, and their thinking problems get worse as their body position changes. In healthy people, brain blood flow increases during hard thinking tasks, but in ME/CFS patients, this normal response is broken—their brains don't increase blood flow when doing difficult mental tasks.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM not requiredPreliminaryEditor reviewed

Clonidine in the treatment of adolescent chronic fatigue syndrome: a pilot study for the NorCAPITAL trial.

Fagermoen, Even, Sulheim, Dag, Winger, Anette et al.·BMC research notes·2012

This small study tested whether a blood pressure medication called clonidine could be safe and helpful for teenagers with ME/CFS. Five teenagers took a low dose of clonidine for two weeks, and researchers measured drug levels in their blood, how their hearts and blood pressure responded to position changes, and any side effects. The medication appeared safe with no serious problems, and it seemed to help improve their body's blood pressure responses.

Autonomic Nervous System
E3 PreliminaryPEM not requiredModerate confidenceObservationalEditor reviewed

Increasing orthostatic stress impairs neurocognitive functioning in chronic fatigue syndrome with postural tachycardia syndrome.

Ocon, Anthony J, Messer, Zachary R, Medow, Marvin S et al.·Clinical science (London, England : 1979)·2012

This study tested whether standing at increasing angles on a tilt table—a procedure that stresses the body's ability to maintain blood flow while upright—makes 'brain fog' worse in people with ME/CFS who also have POTS (a condition causing rapid heartbeat when standing). Researchers found that when people with CFS/POTS stood at steeper angles while doing concentration and memory tests, their performance got worse compared to healthy people, suggesting that orthostatic stress (the challenge of staying upright) does interfere with thinking and memory.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Polymorphisms of adrenergic cardiovascular control genes are associated with adolescent chronic fatigue syndrome.

Sommerfeldt, Line, Portilla, Helene, Jacobsen, Line et al.·Acta paediatrica (Oslo, Norway : 1992)·2011

This study looked at genetic differences in genes that control how the body responds to stress and manages heart rate and blood pressure in teenagers with ME/CFS. Researchers found that people with ME/CFS were more likely to have certain genetic variations in two specific genes (COMT and the β₂-adrenergic receptor) compared to healthy people. These genetic differences may affect how well the body's autonomic nervous system (which controls automatic body functions) works during physical stress.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

Blood pressure variability and closed-loop baroreflex assessment in adolescent chronic fatigue syndrome during supine rest and orthostatic stress.

Wyller, Vegard Bruun, Barbieri, Riccardo, Saul, J Philip·European journal of applied physiology·2011

This study looked at how the nervous system controls heart rate and blood pressure in teenagers with ME/CFS compared to healthy peers. Researchers found that teenagers with ME/CFS had less flexible blood pressure responses and their bodies shifted more toward 'fight or flight' nervous system activation when standing or experiencing mild stress, suggesting their autonomic nervous system (which controls these functions automatically) may not work as efficiently.

Autonomic Nervous System
E3 PreliminaryPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Neuroendocrine and immune contributors to fatigue.

Silverman, Marni N, Heim, Christine M, Nater, Urs M et al.·PM & R : the journal of injury, function, and rehabilitation·2010

This review explores how three body systems—the stress response system, the nervous system, and the immune system—may work together to cause the overwhelming tiredness experienced in ME/CFS. The researchers found that people with chronic fatigue often have an underactive stress-response system, an overactive fight-or-flight response, and immune system imbalances. Understanding how these systems interact may help explain why rest alone doesn't always resolve the fatigue.

Autonomic Nervous SystemImmune System
E3 PreliminaryPEM not requiredPreliminaryMethods-PaperEditor reviewed

Efficiency evaluation of autonomic heart control by using the principal component analysis of ECG P-wave.

Krisciukaitis, A, Simoliuniene, R, Tamosiunas, M et al.·Methods of information in medicine·2010

This study developed a new computer method to measure how well the heart's nerves (autonomic nervous system) work by analyzing changes in the electrical activity of the heart during a simple tilt test, where a person moves from lying down to standing up. The researchers tested this method in healthy people and those with heart rhythm problems, and found it could detect differences in how the heart responds to position changes. This type of measurement might eventually help doctors diagnose problems with heart control earlier.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Can sustained arousal explain the Chronic Fatigue Syndrome?

Wyller, Vegard B, Eriksen, Hege R, Malterud, Kirsti·Behavioral and brain functions : BBF·2009

This study proposes that ME/CFS may be caused by the body getting stuck in a constant state of high alert, similar to being continuously stressed. This sustained arousal could develop after infections or emotional stress, especially in people with certain genetic traits or personality types. The researchers suggest this constant activation creates harmful cycles affecting the immune system, hormones, muscles, and thinking—ultimately leading to the overwhelming fatigue that defines ME/CFS.

Autonomic Nervous SystemImmune System
E3 PreliminaryPEM not requiredPreliminaryObservationalEditor reviewed

[Evaluation of fatigue by using acceleration plethysmography].

Yamaguti, Kouzi·Nihon rinsho. Japanese journal of clinical medicine·2007

Researchers tested a new device called acceleration plethysmography to measure fatigue in ME/CFS patients. This device tracks tiny blood vessel changes and nervous system activity in the fingertip. The study found that fatigue levels were connected to specific patterns in these measurements, suggesting this tool might help doctors objectively measure ME/CFS fatigue in the future.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Treatment of chronic fatigue and orthostatic intolerance with propranolol.

Wyller, Vegard Bruun, Thaulow, Erik, Amlie, Jan P·The Journal of pediatrics·2007

This study looked at a teenager with ME/CFS who also experienced dizziness and fainting when standing up (orthostatic intolerance). The doctors treated this teen with propranolol, a blood pressure medication that slows the heart rate. The case suggests that an overactive stress-response system in the nervous system might contribute to ME/CFS symptoms, and that a simple tilt test could help identify patients who might benefit from this type of treatment.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

[School phobia and childhood chronic fatigue syndrome (CCFS)].

Tomoda, Akemi·Nihon rinsho. Japanese journal of clinical medicine·2007

This review examines childhood chronic fatigue syndrome (CCFS), a serious condition where children experience extreme tiredness that cannot be explained by other medical or mental health problems. Children with CCFS often struggle with memory and concentration, sleep problems, and symptoms related to their nervous system. The authors suggest that CCFS may involve changes in how the brain functions, which could explain why patients experience fatigue, thinking difficulties, and memory problems.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Sympathomimetic amine therapy may improve refractory gastroparesis similar to its effect on chronic pelvic pain--case report.

Boimel, P, Check, J H, Katsoff, D·Clinical and experimental obstetrics & gynecology·2007

This case report describes one patient with ME/CFS who had severe stomach emptying problems (gastroparesis) that didn't respond to standard treatments. When she was given a stimulant medication called dextroamphetamine, her stomach symptoms improved significantly and stayed better for at least eight months. The authors suggest this type of medication might help some people with refractory gastroparesis, similar to how it may help other ME/CFS-related symptoms.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

[Autonomic function and child chronic fatigue syndrome].

Tanaka, Hidetaka·Nihon rinsho. Japanese journal of clinical medicine·2007

This review examined how the autonomic nervous system—the part of your nervous system that controls automatic functions like heart rate and blood pressure—might be involved in childhood ME/CFS. Researchers found that about one-third of children with ME/CFS had problems regulating their blood pressure and heart rate when standing up, a condition called orthostatic dysregulation. While some studies suggested increased sympathetic nervous system activity, the findings were not consistent across all research.

Autonomic Nervous System
E3 PreliminaryPEM unclearModerate confidenceCross-SectionalEditor reviewed

Abnormal thermoregulatory responses in adolescents with chronic fatigue syndrome: relation to clinical symptoms.

Wyller, Vegard Bruun, Godang, Kristin, Mørkrid, Lars et al.·Pediatrics·2007

This study looked at how the body controls temperature in adolescents with ME/CFS compared to healthy teenagers. Researchers found that people with ME/CFS have abnormal responses to temperature changes, with their bodies struggling to regulate heat and cold properly. The study suggests this problem may be related to dysfunction in the nervous system's control of stress hormones like adrenaline.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryObservationalEditor reviewed

The effect of brief exercise cessation on pain, fatigue, and mood symptom development in healthy, fit individuals.

Glass, Jennifer M, Lyden, Angela K, Petzke, Frank et al.·Journal of psychosomatic research·2004

This study looked at whether stopping exercise for just one week could trigger pain, fatigue, or mood problems in healthy people who exercise regularly. Researchers found that 8 out of 18 fit volunteers developed these symptoms after a week without exercise, and these people had weaker stress-response systems (measured by cortisol levels, immune cells, and heart rate patterns) at the start of the study. This suggests some healthy people may naturally have less active biological stress systems and may actually rely on regular exercise to keep their symptoms suppressed.

Autonomic Nervous SystemImmune System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Midodrine treatment for chronic fatigue syndrome.

Naschitz, J, Dreyfuss, D, Yeshurun, D et al.·Postgraduate medical journal·2004

This study reports on one patient with severe ME/CFS who was treated with midodrine, a medication that helps regulate blood pressure and heart rate control. The patient's symptoms of dysautonomia (problems with the autonomic nervous system that controls automatic body functions) improved with this treatment, and their fatigue also improved. This suggests that treating the autonomic nervous system dysfunction may help some people with ME/CFS feel better.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Dysautonomia in chronic fatigue syndrome: facts, hypotheses, implications.

Naschitz, Jochanan E, Yeshurun, Daniel, Rosner, Itzhak·Medical hypotheses·2004

This study looked at whether people with ME/CFS have problems with their autonomic nervous system—the part that automatically controls heart rate and blood pressure. Researchers found a distinctive pattern of dysautonomia (autonomic dysfunction) in ME/CFS patients that differs from other conditions, and they developed two scoring systems to help identify it. A small pilot study suggested that treating this dysautonomia with a medication called midodrine improved both the autonomic problems and fatigue symptoms.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Physiology and pathophysiology of the 5-HT3 receptor.

Färber, L, Haus, U, Späth, M et al.·Scandinavian journal of rheumatology. Supplement·2004

This review examines how a specific brain chemical receptor called 5-HT3 works in the body and what happens when it malfunctions. The researchers found that blocking this receptor with certain medications may help treat several conditions, including ME/CFS, by reducing symptoms like nausea, pain, and anxiety. However, scientists still don't fully understand exactly how this receptor causes problems in these different illnesses.

Pain and SensitizationAutonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryMechanisticEditor reviewed

Acetylcholine mediated vasodilatation in the microcirculation of patients with chronic fatigue syndrome.

Spence, V A, Khan, F, Kennedy, G et al.·Prostaglandins, leukotrienes, and essential fatty acids·2004

This study looked at how blood vessels in ME/CFS patients respond to acetylcholine, a chemical messenger in the body. Normally, blood vessels become less responsive to acetylcholine in disease, but researchers found the opposite in ME/CFS patients—their blood vessels were unusually sensitive to it. This unusual sensitivity might help explain why many ME/CFS patients experience problems with blood flow and circulation.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

Cerebral and systemic hemodynamics changes during upright tilt in chronic fatigue syndrome.

Razumovsky, Alexander Y, DeBusk, Karen, Calkins, Hugh et al.·Journal of neuroimaging : official journal of the American Society of Neuroimaging·2003

When people with ME/CFS stand up quickly, they often experience dizziness and fainting. This study used ultrasound to measure blood flow in the brain during a tilt test and compared it between ME/CFS patients and healthy people. The researchers found that blood flow patterns in the brain were actually similar between the two groups, even though ME/CFS patients felt symptoms faster.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Chronic fatigue syndrome and eating disorders: concurrence or coincidence?

Fisher, Martin, Krilov, Leonard R, Ovadia, Marc·International journal of adolescent medicine and health·2002

This study looked at four adolescent patients who had both an eating disorder and ME/CFS at the same time. In all four cases, the eating disorder appeared first, followed later by ME/CFS symptoms. The authors explored whether these two conditions might be related through common causes, whether an eating disorder could trigger ME/CFS, or whether they simply occurred together by chance.

Autonomic Nervous System
E3 PreliminaryPEM unclearWeak / uncertainEditorialEditor reviewed

Chiari I malformation as a cause of orthostatic intolerance symptoms: a media myth?

Garland, E M, Robertson, D·The American journal of medicine·2001

Some people with ME/CFS and fibromyalgia have heard that a brain condition called Chiari I malformation might be causing their symptoms, especially dizziness and fainting when standing up. This editorial reviews whether that claim is actually supported by scientific research and concludes that there is very little reliable evidence backing up this connection, despite media coverage and patient discussions online.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryObservationalEditor reviewed

Role of impaired lower-limb venous innervation in the pathogenesis of the chronic fatigue syndrome.

Streeten, D H·The American journal of the medical sciences·2001

This study found that people with ME/CFS have problems with how blood vessels in their feet respond to stress. When standing up, their blood pressure drops abnormally after a delay, and their foot veins don't tighten properly in response to a hormone (norepinephrine) that normally helps maintain blood pressure. This suggests that the nerves controlling blood vessels in the legs may not be working correctly in ME/CFS.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryObservationalEditor reviewed

The roles of orthostatic hypotension, orthostatic tachycardia, and subnormal erythrocyte volume in the pathogenesis of the chronic fatigue syndrome.

Streeten, D H, Thomas, D, Bell, D S·The American journal of the medical sciences·2000

This study found that many ME/CFS patients experience a sudden drop in blood pressure and abnormal heart rate acceleration when standing up, along with symptoms like dizziness. The researchers discovered that low red blood cell volume was present in most patients tested, and that wearing inflatable compression pants could quickly reverse these standing problems. This suggests that problems with blood pooling in the legs when upright may contribute to ME/CFS symptoms.

Autonomic Nervous System
E3 PreliminaryPEM not requiredModerate confidenceCross-SectionalEditor reviewed

Autonomic nervous system dysfunction in adolescents with postural orthostatic tachycardia syndrome and chronic fatigue syndrome is characterized by attenuated vagal baroreflex and potentiated sympathetic vasomotion.

Stewart, J M·Pediatric research·2000

This study looked at how the nervous system controls heart rate and blood pressure in adolescents with ME/CFS and POTS when they stand up or tilt their head upward. Researchers found that both groups had similar problems: their bodies couldn't properly regulate heart rate through the vagus nerve (which normally helps calm the heart), and their blood vessels were overly tense. This mismatch may explain why these patients experience dizziness, rapid heartbeat, and fatigue when standing.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Does severe nutcracker phenomenon cause pediatric chronic fatigue?

Takahashi, Y, Ohta, S, Sano, A et al.·Clinical nephrology·2000

Researchers found that 9 children with chronic fatigue all had a rare blood vessel condition called nutcracker phenomenon, where a vein gets compressed and restricts blood flow. These children also had symptoms of autonomic dysfunction (problems with automatic body functions like heart rate and blood pressure) and were originally thought to have psychological problems. The study suggests that this vascular compression might be connected to their fatigue and other symptoms.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Chronic fatigue syndrome: a hypothesis focusing on the autonomic nervous system.

Pagani, M, Lucini, D·Clinical science (London, England : 1979)·1999

This study looked at whether ME/CFS might be caused by problems with the autonomic nervous system—the part of your nervous system that controls automatic functions like heart rate and blood pressure. The researchers measured how the heart's electrical activity varied in ME/CFS patients and found signs suggesting their nervous systems were stuck in a 'revved up' state at rest but didn't respond normally to challenges.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

The importance of orthostatic intolerance in the chronic fatigue syndrome.

Schondorf, R, Freeman, R·The American journal of the medical sciences·1999

This review examines how problems with standing up (orthostatic intolerance) are connected to ME/CFS. Many people with ME/CFS experience symptoms like dizziness, fatigue, trouble concentrating, shaking, and nausea when standing or sitting upright. The authors review what we know about this connection, including how to diagnose it, what tests can help, what might cause it, and how it might be treated.

Autonomic Nervous SystemDiagnostics
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

The connection between chronic fatigue syndrome and neurally mediated hypotension.

Wilke, W S, Fouad-Tarazi, F M, Cash, J M et al.·Cleveland Clinic journal of medicine·1998

Some ME/CFS patients experience a problem where their blood pressure drops abnormally when they stand up, a condition called neurally mediated hypotension. This review examines research showing that this blood pressure response may be linked to ME/CFS symptoms. Understanding this connection could help explain why some patients feel worse with certain activities and may guide treatment options.

Autonomic Nervous System
E3 PreliminaryPEM not requiredWeak / uncertainReview-NarrativeEditor reviewed

[No strong evidence of disturbed regulation of blood pressure in chronic fatigue syndrome].

Smit, A A, Bolweg, N M, Lenders, J W et al.·Nederlands tijdschrift voor geneeskunde·1998

Some ME/CFS patients experience dizziness or fainting when standing up, and researchers wondered if this was due to problems controlling blood pressure. This review looked at four studies that tested this by having patients lie flat and then tilt them upright to see how their bodies responded. While some patients did show heart rate increases or fainting, many of these patients already had these symptoms before testing, making it unclear whether the problem is truly a core feature of ME/CFS or something else.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

Neurally mediated hypotension and autonomic dysfunction measured by heart rate variability during head-up tilt testing in children with chronic fatigue syndrome.

Stewart, J, Weldon, A, Arlievsky, N et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·1998

This study looked at how the nervous system controls heart rate in children with ME/CFS during a tilt test (where patients lie flat then are gradually tilted upright). Researchers found that children with ME/CFS had much lower heart rate variability—a measure of how well the nervous system adjusts the heart—compared to children who faint from other causes and healthy controls. When tilted, children with ME/CFS did not show the normal nervous system adjustments that other groups showed, suggesting their autonomic nervous system (which controls involuntary functions) may not be working properly.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Possible relationship between chronic fatigue and postural tachycardia syndromes.

De Lorenzo, F, Hargreaves, J, Kakkar, V V·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·1996

This study looked at five people with ME/CFS who experienced symptoms like dizziness, blurred vision, and heart palpitations when standing up. When these patients were tested while lying on a tilting table that slowly moved them upright, researchers found that their blood pressure dropped and heart rate increased significantly. This suggests that some ME/CFS patients may have a condition called postural tachycardia syndrome, which affects how the body manages blood pressure during position changes.

Autonomic Nervous System
E3 PreliminaryPEM requiredPreliminaryCase-ControlEditor reviewed

Is neurally mediated hypotension an unrecognised cause of chronic fatigue?

Rowe, P C, Bou-Holaigah, I, Kan, J S et al.·Lancet (London, England)·1995

This study looked at whether a condition called neurally mediated hypotension—where blood pressure drops suddenly when standing up—might be causing chronic fatigue in some patients. Researchers tested seven teenagers with severe fatigue using a tilt-table test (which gradually tilts the body upright) and found that all seven experienced significant drops in blood pressure. Four of these patients improved when treated with specific heart medications, suggesting this condition may contribute to some cases of ME/CFS.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Testing of vestibular function: an adjunct in the assessment of chronic fatigue syndrome.

Furman, J M·Reviews of infectious diseases·1991

Many people with ME/CFS experience dizziness and balance problems, but doctors don't fully understand why. This study looked at whether problems with the inner ear (the system that helps control balance) might explain these symptoms. The researchers tested the vestibular system—which controls balance and eye movement—using specialized equipment to see if people with ME/CFS had measurable abnormalities in how this system works.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Monitoring of cardiorespiratory vagal desynchrony using novel biomarkers derived from smartwatch electrocardiograms in a patient recovering from long COVID: case report.

Kranck, Gustaf, Ståhlberg, Marcus, Andersson, Ulf et al.·European heart journal. Case reports·2025

Researchers tracked one long COVID patient over time using a smartwatch to record heart activity while he was sitting and standing. They noticed that when his fatigue improved, his heart's electrical patterns also normalized, suggesting smartwatch recordings could help monitor autonomic dysfunction (when the nervous system struggles to control heart rate and blood pressure). This simple at-home method may offer a practical way for patients to track their own recovery.

Autonomic Nervous System
E3 PreliminaryPEM unclearModerate confidenceGuidelineEditor reviewed

Improving quality in adult long covid services: Findings from the LOCOMOTION quality improvement collaborative.

Darbyshire, Julie, Greenhalgh, Trisha, Bakerly, Nawar D et al.·Clinical medicine (London, England)·2024

This study looked at how ten long COVID clinics across the UK could improve their care for patients by sharing what they were learning with each other. From 2021 to 2023, clinic staff and patients met regularly to discuss the best ways to help people with long COVID, focusing on problems like breathing difficulties, heart rate issues, tiredness, and brain fog. The team created practical guides to help doctors provide better, more consistent care.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM unclearPreliminaryEditor reviewed

Inspiratory muscle training improves autonomic function in myalgic encephalomyelitis/chronic fatigue syndrome and post-acute sequelae of SARS-CoV-2: A pilot study.

Edgell, Heather, Pereira, Tania J, Kerr, Kathleen et al.·Respiratory physiology & neurobiology·2025

This study tested whether a simple breathing exercise program could help people with ME/CFS and Long COVID feel better. For 8 weeks, participants practiced strengthening their breathing muscles. People in all groups—including those with ME/CFS and Long COVID—showed improvements in how far they could walk, their heart rate, sleep quality, and how their nervous system functioned. Those with ME/CFS also noticed less pain and better blood vessel function.

SleepAutonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryCross-SectionalEditor reviewed

Autonomic phenotyping, brain blood flow control, and cognitive-motor-integration in Long COVID and myalgic encephalomyelitis/chronic fatigue syndrome: A pilot study.

Badhwar, Smriti, Pereira, Tania J, Kerr, Kathleen et al.·Autonomic neuroscience : basic & clinical·2025

This study compared how the nervous systems of ME/CFS patients, Long COVID patients, and healthy people respond to physical stress tests like breathing different air mixtures and tilting upright. The researchers found that ME/CFS and Long COVID patients had different patterns of problems: ME/CFS patients showed difficulty controlling blood flow to the brain during one test, which was linked to coordination problems, while Long COVID patients had lower oxygen levels when upright and their nervous systems didn't adapt as well.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Cerebral Blood Flow in Orthostatic Intolerance.

Khan, Muhammad Shahzeb, Miller, Amanda J, Ejaz, Arooba et al.·Journal of the American Heart Association·2025

When you stand up, your body normally adjusts blood flow to keep your brain supplied with oxygen. Some people have problems with this adjustment, causing dizziness, fatigue, or fainting—a condition called orthostatic intolerance. This review explains that many ME/CFS and long COVID patients have reduced blood flow to the brain when standing, even though their heart rate and blood pressure look normal on standard tests. The authors review different tools doctors can use to actually measure brain blood flow, rather than just relying on heart rate and blood pressure readings.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryObservationalEditor reviewed

Head-down tilt reduces the heart rate in postural tachycardia syndrome in acute setting: a pilot study.

Novak, Peter·Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology·2024

This small study tested whether tilting the head downward slightly could help people with POTS (a condition causing rapid heart rate when standing). Researchers found that a 10-degree head-down tilt for 2 minutes safely reduced heart rate by about 10% and improved blood oxygen levels. Four of the seven patients tested also had ME/CFS, suggesting this approach might have potential for multiple related conditions.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Cardiac Geometry and Function in Patients with Reflex Syncope.

Coseriu, Giorgia, Schiop-Tentea, Patricia, Apetrei, Csilla-Andrea et al.·Journal of clinical medicine·2024

This review examines how the size and function of the heart relate to fainting episodes in people with reflex syncope. Researchers found that people with smaller hearts and very forceful heartbeats are more prone to fainting, and this pattern is also seen in some people with chronic fatigue syndrome. Understanding these heart differences may help doctors predict who will faint again and choose better treatments.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

The interplay between Sars-Cov-2 infection related cardiovascular diseases and depression. Common mechanisms, shared symptoms.

Gonjilashvili, Ana, Tatishvili, Sophio·American heart journal plus : cardiology research and practice·2024

This review examines how COVID-19 can affect both the heart and mental health, and why these problems often occur together. The authors explain that inflammation, unhealthy lifestyle changes, and communication between organs may all play a role. They note that long COVID shares many symptoms with heart and brain problems—like fatigue, brain fog, dizziness, chest pain, and depression—which is why patients need care from multiple medical specialists.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Dysautonomia following Lyme disease: a key component of post-treatment Lyme disease syndrome?

Adler, Brittany L, Chung, Tae, Rowe, Peter C et al.·Frontiers in neurology·2024

This review examines how Lyme disease can damage the autonomic nervous system—the part of your nervous system that controls automatic body functions like heart rate, blood pressure, and digestion. The authors argue that this autonomic dysfunction may explain why some people with Lyme disease develop persistent, widespread symptoms similar to those seen in ME/CFS and long COVID. They review existing evidence and propose possible mechanisms for how the Lyme disease bacteria might cause these ongoing problems.

Autonomic Nervous System
E3 PreliminaryPEM unclearModerate confidenceReview-NarrativeEditor reviewed

Cardiovascular and haematological pathology in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS): A role for viruses.

Nunes, Jean M, Kell, Douglas B, Pretorius, Etheresia·Blood reviews·2023

This review examines how the heart, blood vessels, and blood clotting system may be affected in ME/CFS. Research shows that ME/CFS patients often have problems with blood flow to the brain, abnormal blood clotting, and damaged blood vessel linings—similar to what happens in Long COVID. These cardiovascular and blood abnormalities may contribute to ME/CFS symptoms and could potentially become targets for new treatments.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryEditor reviewed

Converging Evidence of Similar Symptomatology of ME/CFS and PASC Indicating Multisystemic Dyshomeostasis.

Marks, David F·Biomedicines·2023

This study found that ME/CFS and long COVID (PASC) cause very similar symptoms in patients. Researchers compared symptom reports from two groups and found they matched about 90% of the time. The authors suggest both conditions may involve the body's control systems (nervous system, hormones, and immune system) getting stuck in a broken state, similar to a thermostat that can't turn off.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryCase-ControlEditor reviewed

A Case Study of Successful Application of the Principles of ME/CFS Care to an Individual with Long COVID.

Petracek, Lindsay S, Broussard, Camille A, Swope, Renee L et al.·Healthcare (Basel, Switzerland)·2023

A 19-year-old developed severe ME/CFS-like symptoms after COVID-19 infection. Doctors used ME/CFS treatment approaches—including physical therapy, heart rate monitoring, and medications for heart and immune problems—and the patient improved significantly over 2.5 years. This case suggests that treatments developed for ME/CFS may also help some long COVID patients.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

A Review of Stellate Ganglion Block as an Adjunctive Treatment Modality.

Kirkpatrick, Kennedy, Khan, Mashfee H, Deng, Yi et al.·Cureus·2023

This review article explores a procedure called stellate ganglion block (SGB), where doctors inject local anesthetic into nerve bundles in the neck to calm an overactive nervous system. The authors suggest that several conditions—including chronic fatigue syndrome, long-COVID, and loss of smell—may share a common problem: too much sympathetic nervous system activity (the 'fight or flight' response). Early case reports suggest SGB might help patients with these conditions when standard treatments don't work, though more research is needed.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Autoimmune Autonomic Dysfunction Syndromes: Potential Involvement and Pathophysiology Related to Complex Regional Pain Syndrome, Fibromyalgia, Chronic Fatigue Syndrome, Silicone Breast Implant-Related Symptoms and Post-COVID Syndrome.

Mahroum, Naim, Shoenfeld, Yehuda·Pathophysiology : the official journal of the International Society for Pathophysiology·2022

This article suggests that several chronic conditions—including ME/CFS, fibromyalgia, long COVID, and complex regional pain syndrome—may share a common cause: the immune system mistakenly producing antibodies that attack the autonomic nervous system (the part of your body that controls automatic functions like heart rate and blood pressure). The authors propose calling these conditions "autoimmune autonomic dysfunction syndromes" to highlight this shared mechanism and potentially help doctors diagnose and treat them more effectively.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

Brain Responses in CFS and TMD to Autonomic Challenges: An Exploratory fMRI Study.

Vuong, Q C, Allison, J R, Finkelmeyer, A et al.·JDR clinical and translational research·2020

This study looked at how the brains of people with ME/CFS respond during a specific breathing test (the Valsalva maneuver) that activates the autonomic nervous system—the part of your nervous system that controls automatic body functions like heart rate and breathing. Researchers compared brain scans of people with ME/CFS who also had jaw pain (temporomandibular disorder) to those with ME/CFS alone and healthy controls. They found that people with both conditions showed stronger brain activity in areas related to pain and fatigue, suggesting that problems with autonomic nervous system control may contribute to both conditions.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Postural orthostatic tachycardia syndrome (POTS): a common but unfamiliar syndrome.

van der Zalm, T, Alsma, J, van de Poll, S W E et al.·The Netherlands journal of medicine·2019

POTS is a condition where standing up quickly causes your heart to beat much faster than normal, and you may feel dizzy, tired, or unwell. This paper describes two different patients with POTS to show how differently the condition can appear from person to person. The authors explain that POTS can overlap with chronic fatigue syndrome and suggest that simple treatments like drinking more water and salt, along with exercise, often help before considering medications.

Autonomic Nervous System
E3 PreliminaryPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Clinical neurophysiology of postural tachycardia syndrome.

Cutsforth-Gregory, Jeremy K, Sandroni, Paola·Handbook of clinical neurology·2019

Postural tachycardia syndrome (POTS) is a condition where your heart rate jumps dramatically when you stand up, causing dizziness, lightheadedness, or other symptoms of not enough blood reaching your brain. It happens five times more often in women than men and can have several different causes, including problems with nerve signals, low blood volume, or deconditioning. Treatment focuses on helping patients stand longer and stay active, using approaches like drinking more fluids, wearing compression socks, and sometimes taking medications.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Managing fatigue in postural tachycardia syndrome (PoTS): The Newcastle approach.

Strassheim, Victoria, Welford, Jenny, Ballantine, Rob et al.·Autonomic neuroscience : basic & clinical·2018

This review examines fatigue in people with PoTS (postural tachycardia syndrome), a condition where heart rate increases abnormally when standing. The authors explain why fatigue happens in PoTS, how it overlaps with ME/CFS, and describe practical approaches doctors can use to help manage it by treating the individual causes of fatigue in each patient.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

HPV vaccination syndrome: A clinical mirage, or a new tragic fibromyalgia model.

Martínez-Lavín, Manuel·Reumatologia clinica·2018

Some people have reported developing chronic pain and autonomic symptoms (problems with heart rate, blood pressure, and sweating) after receiving the HPV vaccine. This article reviews whether this connection is real and suggests that if it exists, these cases might share similarities with fibromyalgia—a condition involving widespread pain and nervous system dysfunction. The authors propose that understanding fibromyalgia's mechanisms could help diagnose and treat patients who develop symptoms after HPV vaccination.

Pain and SensitizationAutonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Fibromyalgia syndrome pathology and environmental influences on afflictions with medically unexplained symptoms.

Albrecht, Phillip J, Rice, Frank L·Reviews on environmental health·2016

This review examines fibromyalgia syndrome (FMS) as a model for understanding conditions with symptoms that are difficult to explain medically. The authors discuss how nerve endings in the skin and stress hormones (particularly estrogen) may play a role in causing widespread pain and fatigue. They propose that environmental stress and past trauma can trigger changes in how the nervous system works, leading to increased pain sensitivity.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Aspects of the non-pharmacological treatment of irritable bowel syndrome.

Eriksson, Elsa Maria, Andrén, Kristina Ingrid, Kurlberg, Göran Karl et al.·World journal of gastroenterology·2015

This article explains how irritable bowel syndrome (IBS) develops through problems in communication between the gut and brain, especially when the body is stressed or has experienced trauma. The authors suggest that combining traditional gastroenterology care with body-mind therapies—which help patients become more aware of their physical sensations—may be more effective than treating the gut alone.

Autonomic Nervous System
E3 PreliminaryPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Postural Tachycardia Syndrome: Beyond Orthostatic Intolerance.

Garland, Emily M, Celedonio, Jorge E, Raj, Satish R·Current neurology and neuroscience reports·2015

This review explains postural tachycardia syndrome (POTS), a condition where your heart rate increases excessively when you stand up, often causing dizziness, fatigue, and other symptoms that improve when lying down. POTS can result from several different underlying problems—such as low blood volume, overactive stress nerves, or problems with small nerves in the legs—and may overlap with other conditions like ME/CFS. Treatment typically involves a combination of lifestyle changes, structured exercise, and sometimes medications.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCross-SectionalEditor reviewed

HPV vaccination syndrome. A questionnaire-based study.

Martínez-Lavín, Manuel, Martínez-Martínez, Laura-Aline, Reyes-Loyola, Paola·Clinical rheumatology·2015

This study looked at people who developed long-lasting pain, fatigue, and heart/blood pressure problems shortly after receiving the HPV vaccine. Researchers used three validated questionnaires to assess 45 people from 13 countries. Most reported muscle pain, tiredness, and dizziness, and after an average of 4 years, 93% still had severe symptoms preventing them from working or going to school.

Pain and SensitizationAutonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Neurovisceral phenotypes in the expression of psychiatric symptoms.

Eccles, Jessica A, Owens, Andrew P, Mathias, Christopher J et al.·Frontiers in neuroscience·2015

This review examines how physical differences in the body's automatic nervous system—the system that controls heart rate, blood pressure, and stress responses—may explain why some people experience anxiety more easily. The authors focus on three conditions: joint hypermobility (loose joints due to collagen differences), postural tachycardia syndrome (rapid heart rate when standing), and fainting with emotional stress. They propose that differences in how the brain controls these bodily functions may make people more vulnerable to anxiety and related conditions.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Neurocardiogenic syncope and associated conditions: insight into autonomic nervous system dysfunction.

Kossaify, Antoine, Kallab, Kamal·Turk Kardiyoloji Dernegi arsivi : Turk Kardiyoloji Derneginin yayin organidir·2013

This study examines why people faint or feel faint due to problems with their autonomic nervous system—the part of your nervous system that controls heart rate, blood pressure, and breathing automatically. The authors review how fainting episodes are connected to several conditions that ME/CFS patients often experience, including migraines, dizziness upon standing, rapid heartbeat with position changes, and chronic fatigue syndrome. They discuss how autonomic dysfunction may explain these related conditions.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryObservationalEditor reviewed

Cervical neuro-muscular syndrome: discovery of a new disease group caused by abnormalities in the cervical muscles.

Matsui, Takayoshi, Ii, Kunio, Hojo, Shuntaro et al.·Neurologia medico-chirurgica·2012

This study suggests that problems in the neck muscles may cause or contribute to a range of symptoms including headaches, dizziness, fatigue, and autonomic problems (issues with automatic body functions like heart rate and blood pressure). The researchers treated patients with neck muscle abnormalities and reported that most patients improved significantly, with success rates ranging from 84-88% depending on the symptom.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Pathogenic mechanisms of idiopathic nonallergic rhinitis.

Baraniuk, James N·The World Allergy Organization journal·2009

This study examines why some people develop chronic nasal symptoms like congestion and runny nose that don't have an obvious allergic cause. Researchers found that this condition may actually involve several different problems: structural issues in the nose, nerve sensitivity problems, and autonomic nervous system dysfunction—the same type of nervous system problem found in ME/CFS.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

POTS versus deconditioning: the same or different?

Joyner, Michael J, Masuki, Shizue·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2008

This review article compares POTS (a condition where heart rate and blood pressure drop abnormally when standing) with the physical deconditioning that happens after long bed rest or spaceflight. The authors suggest that both conditions may share similar causes and that carefully structured exercise training might help patients with POTS, ME/CFS, and fibromyalgia, while acknowledging the medical community must remain empathetic to patients with these complex conditions.

Autonomic Nervous System
E3 PreliminaryPEM not requiredModerate confidenceReview-NarrativeEditor reviewed

Fainting freshmen and sinking sophomores: cardiovascular issues of the adolescent.

DiVasta, Amy Desrochers, Alexander, Mark E·Current opinion in pediatrics·2004

This review article explains that fainting is common in teenagers, but most cases are not caused by serious heart problems. Doctors can identify the few teenagers with real heart disease using a detailed patient history, physical examination, and an electrocardiogram (ECG). The article emphasizes that teenagers with certain conditions—including chronic fatigue syndrome, eating disorders, and exercise-related fainting—need extra careful evaluation because their heart problems may be more serious or harder to manage.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Chiari type I malformation revisited: diagnosis and treatment.

Cheng, Joseph S, Nash, John, Meyer, Glenn A·The neurologist·2002

Chiari type I is a condition where brain tissue (cerebellar tonsils) extends into the spinal canal, potentially compressing the lower brain and upper spinal cord. This article reviews how doctors diagnose and treat this condition, and discusses possible links between Chiari I and ME/CFS, fibromyalgia, and other neurological symptoms. The authors note that in severe cases, Chiari I can cause permanent nerve damage, but better imaging and treatments are being developed.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Neuroendocrine mechanisms in fibromyalgia-chronic fatigue.

Buskila, D, Press, J·Best practice & research. Clinical rheumatology·2001

This review examines why fibromyalgia and ME/CFS cause such similar symptoms like fatigue, pain, and problems with the nervous system. Researchers found that both conditions involve problems with hormones, how the body processes pain, and how the autonomic nervous system (which controls automatic body functions) works. The study suggests these conditions may share the same underlying cause: dysfunction in the central nervous system.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Fibromyalgia, chronic fatigue syndrome, and myofascial pain syndrome.

Buskila, D·Current opinion in rheumatology·2001

This review examined fibromyalgia (FM), chronic fatigue syndrome (CFS), and related pain conditions across different countries. Researchers found that pain sensitivity involves brain chemistry (including a system called NMDA), hormone imbalances, and nervous system problems. CFS was found in about 0.4% of a large community sample, with many children recovering well, though the study notes that no major new treatments were tested during this period.

Pain and SensitizationAutonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryEditorialEditor reviewed

Potential mechanisms in chemical intolerance and related conditions.

Clauw, D J·Annals of the New York Academy of Sciences·2001

Many people with ME/CFS, fibromyalgia, and related conditions experience chemical intolerance alongside other symptoms like pain and fatigue. This study reviews research suggesting that these conditions share common biological problems, particularly in how the nervous system processes sensory information—making everyday smells, sounds, or lights feel unusually unpleasant or overwhelming. While stress and worry can sometimes make symptoms worse, the evidence shows that physical changes in the body's sensory processing are doing much of the heavy lifting in causing symptoms.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Fibromyalgia, chronic fatigue syndrome, and myofascial pain syndrome.

Buskila, D·Current opinion in rheumatology·2000

This review article examines the connections between fibromyalgia, chronic fatigue syndrome (ME/CFS), and myofascial pain syndrome. Researchers found that people with these conditions often have tender points in their muscles, hormonal imbalances affecting stress response, and possible immune system involvement. The study suggests that talking therapies like cognitive behavioral therapy may help manage chronic pain in these conditions, and that children and adolescents with these illnesses often improve over time.

Pain and SensitizationAutonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Sympathetic nervous system function in fibromyalgia.

Petzke, F, Clauw, D J·Current rheumatology reports·2000

This review examines how the sympathetic nervous system—the part that controls your 'fight or flight' stress response—works differently in fibromyalgia patients. Researchers looked at various ways to measure sympathetic function, including heart rate changes, stress hormone levels, and physical responses to stress. The authors also compared findings in fibromyalgia to similar conditions like ME/CFS, irritable bowel syndrome, and migraine to identify common patterns.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Orthostatic intolerance and chronic fatigue syndrome associated with Ehlers-Danlos syndrome.

Rowe, P C, Barron, D F, Calkins, H et al.·The Journal of pediatrics·1999

This study looked at 12 teenagers who had both ME/CFS and a connective tissue condition called Ehlers-Danlos syndrome (EDS). All of them also experienced problems with blood pressure and heart rate when standing up (orthostatic intolerance). The researchers found that abnormal connective tissue in blood vessels may cause blood to pool in the legs when standing, which could explain why these conditions often occur together.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Autonomic neuropathies.

Low, P A·Current opinion in neurology·1998

This review explores how problems with the autonomic nervous system—the part of your nervous system that controls automatic functions like heart rate and temperature regulation—may play a role in several conditions, including ME/CFS. The author discusses how antibodies (immune proteins) targeting autonomic structures are found in some diseases, and notes that some autonomic problems can be treated with medications like midodrine or erythropoietin.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

Fibromyalgia, chronic fatigue syndrome, and myofascial pain syndrome.

Goldenberg, D L·Current opinion in rheumatology·1997

This review examines three related conditions—fibromyalgia, ME/CFS, and myofascial pain syndrome—and discusses ongoing challenges in diagnosing and treating them. The study found that psychiatric conditions are not a core feature of these diseases, but rather reflect that people with these conditions are more likely to seek medical help. The researchers identified that a blood pressure problem called neurally mediated hypotension may play a role in ME/CFS, and that treating patients in multidisciplinary groups (rather than in isolation) showed more promise than traditional individual treatments.

Autonomic Nervous SystemDiagnostics
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Neurotic, neuromuscular and autonomic nervous form of magnesium imbalance.

Durlach, J, Bac, P, Durlach, V et al.·Magnesium research·1997

This review discusses how low magnesium levels in the body can affect the nervous system and cause symptoms like fatigue, muscle twitching, heart palpitations, and breathing problems. The authors describe how magnesium deficiency can mimic or contribute to chronic fatigue syndrome and similar conditions, and they explain tests (like EMG and blood tests) that can help diagnose this problem. They also suggest that taking magnesium supplements by mouth at appropriate doses may help relieve these symptoms.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

The pathogenesis of chronic pain and fatigue syndromes, with special reference to fibromyalgia.

Clauw, D J·Medical hypotheses·1995

This paper reviews what doctors and researchers knew in 1995 about fibromyalgia and similar conditions that cause chronic pain and tiredness. The authors noticed that fibromyalgia overlaps significantly with chronic fatigue syndrome, migraines, irritable bowel syndrome, and mood disorders, suggesting these conditions may share common underlying causes rather than being completely separate diseases.

SleepAutonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryObservationalEditor reviewed

Pyridostigmine improves hand grip strength in patients with myalgic encephalomyelitis/chronic fatigue syndrome.

Schlömer, Ella, Stein, Elisa, Kedor, Claudia et al.·Frontiers in neuroscience·2025

This small study tested whether a medication called pyridostigmine could help ME/CFS patients recover hand grip strength after exertion. Twenty patients with ME/CFS showed significant muscle weakness and fatigue. When given pyridostigmine, their hand strength improved by about 2.6 kg after one hour, compared to a loss of 4.65 kg without the medication. The medication also appeared to help with blood pressure responses when standing up.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeEditor reviewed

TMD and chronic pain: a current view.

Furquim, Bruno D'Aurea, Flamengui, Lívia Maria Sales Pinto, Conti, Paulo César Rodrigues·Dental press journal of orthodontics·2015

This review examines how temporomandibular disorders (jaw joint and muscle problems) develop and persist. The authors found that chronic muscle pain in the jaw works similarly to other widespread pain conditions like fibromyalgia and ME/CFS—through a process called central sensitization where the nervous system becomes overly sensitive to pain signals. They explain that genetics and nervous system function influence whether symptoms improve or worsen.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

[Review of the effects of mindfulness meditation on mental and physical health and its mechanisms of action].

Ngô, Thanh-Lan·Sante mentale au Quebec·2013

This review looked at whether mindfulness meditation—a practice of focused attention and acceptance—can help improve both mental and physical health. The authors found that mindfulness may reduce stress, ease chronic pain and fatigue, improve sleep, and help the body's immune system work better. They also describe how meditation appears to change the way the brain works, particularly in areas that control emotions, attention, and how we perceive physical sensations.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryObservationalEditor reviewed

Orthostatic panic attacks among Vietnamese refugees.

Hinton, Devon E, Hinton, Ladson, Tran, Minh et al.·Transcultural psychiatry·2007

This study looked at Vietnamese refugees who experienced panic attacks triggered by standing up quickly from a sitting or lying position (orthostatic dizziness). The researchers found that these panic attacks were common among this group and were often linked to trauma memories and cultural beliefs about health. The study suggests that doctors treating Vietnamese refugees should check for and treat these specific panic attacks as part of their care.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryMechanisticEditor reviewed

Cardiovascular systemic regulation by plantar surface stimulation.

Madhavan, Guruprasad, Stewart, Julian M, McLeod, Kenneth J·Biomedical instrumentation & technology·2006

This study tested whether gentle vibrations applied to the bottom of the foot could help stabilize blood pressure and heart rate when people sit down. Researchers found that vibrations at a specific frequency (around 44 Hz) significantly reduced the normal drop in blood pressure that occurs with sitting, and were especially helpful for people whose blood pressure drops excessively.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryMethods-PaperEditor reviewed

Search for disease-specific cardiovascular reactivity patterns: developing the methodology.

Naschitz, Jochanan E, Rozenbaum, Michael, Fields, Madeline et al.·Clinical science (London, England : 1979)·2005

Researchers developed new methods to detect specific patterns in how the body's heart rate and blood pressure respond to physical stress (tilting upright) in people with familial Mediterranean fever (FMF). They found that people with FMF show distinctive cardiovascular responses that can be measured and used to help identify the condition. The study shows this approach might also work for other diseases, including ME/CFS.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryCase-ControlEditor reviewed

Case reports and review of Postural Orthostatic Tachycardia syndrome (POTS).

Carothers, Becky, Schmidt, Lori, Puri, Vinay·The Journal of the Kentucky Medical Association·2003

POTS is a condition where your heart rate increases too much when you stand up, and less blood flows to your brain, causing dizziness and fainting. This paper describes two patients with POTS who needed different levels of treatment—one managed at home and one needing hospital care. The authors point out that POTS is probably more common than doctors realize and is sometimes mistaken for chronic fatigue syndrome or other conditions.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryMechanisticEditor reviewed

Familial corticosteroid-binding globulin deficiency due to a novel null mutation: association with fatigue and relative hypotension.

Torpy, D J, Bachmann, A W, Grice, J E et al.·The Journal of clinical endocrinology and metabolism·2001

This study examined a family with a genetic mutation affecting a protein called corticosteroid-binding globulin (CBG), which helps transport the stress hormone cortisol in the blood. People with this mutation had unusually low blood pressure and chronic fatigue—in fact, 86% of affected adults met criteria for chronic fatigue syndrome. The findings suggest that problems with how the body handles cortisol may contribute to fatigue disorders.

Autonomic Nervous System
E3 PreliminaryPEM not requiredPreliminaryReview-NarrativeEditor reviewed

Ruscus aculeatus (butcher's broom) as a potential treatment for orthostatic hypotension, with a case report.

Redman, D A·Journal of alternative and complementary medicine (New York, N.Y.)·2000

Many people with ME/CFS experience orthostatic hypotension—a sudden drop in blood pressure when standing up—which can be severely disabling. This paper reviews why existing medications for this condition often don't work well and proposes that Ruscus aculeatus (butcher's broom), a plant-based supplement used in Europe, might help by improving blood vessel function and preventing blood from pooling in the legs.

Autonomic Nervous System
E0 ConsensusPEM not requiredModerate confidenceSystematic-ReviewMachine-drafted

Postural tachycardia syndrome and other forms of orthostatic intolerance in Ehlers-Danlos syndrome.

Roma, Maria, Marden, Colleen L, De Wandele, Inge et al.·Autonomic neuroscience : basic & clinical·2018

This review looked at research connecting two conditions: orthostatic intolerance (difficulty standing up without dizziness, rapid heartbeat, or fainting) and Ehlers-Danlos syndrome (a connective tissue disorder causing loose joints and flexible skin). The researchers found that people with Ehlers-Danlos syndrome experience orthostatic intolerance symptoms much more often than healthy people, and these symptoms significantly affect their quality of life.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceMachine-drafted

Autonomic dysfunction in myalgic encephalomyelitis and chronic fatigue syndrome: comparing self-report and objective measures.

Kemp, Jane, Sunnquist, Madison, Jason, Leonard A et al.·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2019

This study looked at whether ME/CFS patients experience problems with their autonomic nervous system—the part that controls heart rate, blood pressure, and other automatic body functions. The researchers compared what patients reported about their symptoms with objective medical tests to see if these matched up, helping doctors understand this aspect of ME/CFS better.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCase-ControlMachine-drafted

Enhanced sensitivity of the peripheral cholinergic vascular response in patients with chronic fatigue syndrome.

Spence, V A, Khan, F, Belch, J J·The American journal of medicine·2000

This study looked at how blood vessels in ME/CFS patients respond to a natural chemical in the body called acetylcholine, which helps control blood vessel widening and narrowing. Researchers compared blood vessel responses in ME/CFS patients versus healthy people and found that ME/CFS patients showed an unusually strong reaction. This finding suggests that the nervous system's control of blood vessels may work differently in ME/CFS.

Autonomic Nervous System
E2 ModeratePEM unclearModerate confidenceCase-ControlMachine-drafted

Dysautonomia in chronic fatigue syndrome vs. fibromyalgia.

Rosner, I, Rozenbaum, M, Naschitz, J E et al.·The Israel Medical Association journal : IMAJ·2000

This study compared how the nervous systems of people with ME/CFS and fibromyalgia function differently, focusing on dysautonomia—problems with the automatic nervous system that controls heart rate, blood pressure, and other body functions. Researchers used a case-control design to examine whether these two conditions show distinct patterns of autonomic dysfunction. The findings help clarify whether ME/CFS and fibromyalgia are separate conditions with different underlying nervous system problems.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryObservationalMachine-drafted

Cardiac sympathetic innervation associates with autonomic dysfunction in chronic fatigue syndrome - a pilot study.

Petrides, George, Zalewski, Pawel, McCulloch, David et al.·Fatigue : biomedicine, health & behavior·2017

This study looked at how the nervous system controls the heart in people with ME/CFS, focusing on a specific part called the sympathetic nervous system. Researchers used specialized imaging to examine nerve connections in the heart and compared them to problems with autonomic function (the automatic nervous system that controls heart rate and blood pressure). The findings suggest that differences in heart nerve connections may be related to why some ME/CFS patients experience autonomic symptoms like dizziness and heart rate changes.

Autonomic Nervous System
E3 PreliminaryPEM unclearModerate confidenceReview-NarrativeMachine-drafted

The head-up tilt test in the diagnosis and management of chronic fatigue syndrome.

Naschitz, Jochanan E, Sabo, Edmond, Dreyfuss, Daniel et al.·The Israel Medical Association journal : IMAJ·2003

This review examines how a simple test called the head-up tilt test might help diagnose and manage ME/CFS. In this test, a patient lies flat and is then tilted upright while doctors measure heart rate and blood pressure changes. The review discusses whether these measurements could reveal problems with how the body controls blood pressure and heart function in ME/CFS patients.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeMachine-drafted

The chronic fatigue syndrome is a disease of the autonomic nervous system. Sometimes.

Freeman, Roy·Clinical autonomic research : official journal of the Clinical Autonomic Research Society·2002

This review article examines whether ME/CFS might be caused by problems with the autonomic nervous system—the part of your body that controls automatic functions like heart rate and blood pressure. The author, Dr. Roy Freeman, discusses evidence suggesting that some ME/CFS patients do show signs of autonomic dysfunction, but emphasizes that this is not true for all patients with the condition.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeMachine-drafted

Narrative Review of Postural Orthostatic Tachycardia Syndrome: Associated Conditions and Management Strategies.

Steinberg, Rebecca S, Dicken, Weston, Cutchins, Alexis·US cardiology·2023

This review examines POTS (Postural Orthostatic Tachycardia Syndrome), a condition where your heart rate jumps too quickly when you stand up, along with other symptoms like dizziness and fatigue. The authors combined research evidence with their clinical experience to explain how POTS is recognized, what other conditions often occur alongside it, and how doctors can treat it. Many patients and doctors find POTS frustrating to diagnose and manage because treatments haven't been well-studied and POTS shares symptoms with other conditions.

Autonomic Nervous System
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeMachine-drafted

[Modern approaches to diagnosis and treatment of postinfectious asthenic syndrome in children].

Nemkova, S A·Zhurnal nevrologii i psikhiatrii imeni S.S. Korsakova·2025

This review article discusses postinfectious asthenic syndrome—a condition causing severe tiredness and weakness that develops after infections like colds, flu, and COVID-19 in children and teenagers. The authors examine how this condition develops, its symptoms, and how a medication called Mexidol may help reduce fatigue and improve thinking, mood, and nervous system problems that often accompany it.

Autonomic Nervous SystemCognitive Impairment
E3 PreliminaryPEM unclearPreliminaryReview-NarrativeMachine-drafted

The Interplay between Oxidative Stress, Exercise, and Pain in Health and Disease: Potential Role of Autonomic Regulation and Epigenetic Mechanisms.

Hendrix, Jolien, Nijs, Jo, Ickmans, Kelly et al.·Antioxidants (Basel, Switzerland)·2020

This review examines how physical activity, pain, and a harmful process called oxidative stress (cellular damage from unstable molecules) interact in both healthy people and those with chronic pain conditions. The authors found that the relationships between these three factors are complicated and depend on the type of exercise and which person is being studied. They suggest that the nervous system's automatic functions and changes in how genes are expressed may help explain why these connections work differently in different people.

Pain and SensitizationAutonomic Nervous System

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