E2 ModerateModerate confidencePEM not requiredCross-SectionalPeer-reviewedReviewed
Standard · 3 min
Does the chronic fatigue syndrome involve the autonomic nervous system?
Freeman, R, Komaroff, A L · The American journal of medicine · 1997 · DOI
Quick Summary
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.
Why It Matters
This study provides objective physiological evidence that autonomic nervous system dysfunction is a real biological feature of ME/CFS, not a psychological artifact. Understanding these abnormalities helps explain debilitating symptoms like orthostatic intolerance and offers a potential window into disease mechanisms, which could guide future diagnostic testing and treatment development.
Observed Findings
CFS patients had significantly elevated baseline heart rate and exaggerated heart rate responses to standing and tilting compared to controls.
Parasympathetic nervous system function (measured by heart rate variability and breathing-related HR changes) was significantly reduced in the CFS group.
Sympathetic nervous system function (measured by blood pressure drops during tilting and Valsalva maneuver) was significantly reduced in the CFS group.
Twenty-five percent of CFS patients had a positive tilt table test, suggesting orthostatic intolerance.
Physical activity level was a significant predictor of autonomic test abnormalities, whereas psychiatric conditions were not.
Inferred Conclusions
ME/CFS patients have measurable abnormalities in both sympathetic and parasympathetic nervous system function that provide a physiological basis for orthostatic intolerance and autonomic symptoms.
The temporal pattern of autonomic symptom onset (46% within 4 weeks of viral infection) is consistent with a postviral autonomic neuropathy.
Cardiovascular deconditioning and/or postviral autonomic nervous system damage may explain the observed autonomic dysfunction.
Remaining Questions
Is autonomic dysfunction a primary pathogenic mechanism in ME/CFS or a secondary consequence of inactivity and deconditioning?
What This Study Does Not Prove
This study does not prove that autonomic dysfunction causes ME/CFS or that it is the primary disease mechanism. The cross-sectional design cannot establish whether autonomic abnormalities are primary pathology or secondary to deconditioning and inactivity. The study also does not establish whether autonomic dysfunction is present in all ME/CFS patients or if it is a subgroup feature.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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