Purpose: To investigate the role of the autonomic nervous system in the symptoms of patients with chronic fatigue syndrome (CFS) and delineate the pathogenesis of the orthostatic intolerance and predisposition to neurally mediated syncope reported in this patient group.

Patients and Methods: Twenty-three CFS patients and controls performed a battery of autonomic function tests. The CFS patients completed questionnaires pertaining to autonomic and CFS symptoms, their level of physical activity, and premorbid and coexisting psychiatric disorders. The relationship between autonomic test results, cardiovascular deconditioning, and psychiatric disorders was examined with multivariate statistics and the evidence that autonomic changes seen in CFS might be secondary to a postviral, idiopathic autonomic neuropathy was explored.

Results: The CFS subjects had a significant increase in baseline (P <0.01) and maximum heart rate (HR) on standing and tilting (both P <0.0001). Tests of parasympathetic nervous system function (the expiratory inspiratory ratio, P <0.005; maximum minus minimum HR difference, P <0.05), were significantly less in the CFS group as were measures of sympathetic nervous system function (systolic blood pressure decrease with tilting, P <0.01; diastolic blood pressure decrease with tilting, P <0.05; and the systolic blood pressure decrease during phase II of a Valsalva maneuver, P <0.05). Twenty-five percent of CFS subjects had a positive tilt table test. The physical activity index was a significant predictor of autonomic test results (resting, sitting, standing, and tilted HR, P <0.05 to P <0.009); and the blood pressure decrease in phase II of the Valvalsa maneuver, P <0.05) whereas premorbid and coexistent psychiatric conditions were not. The onset of autonomic symptoms occurred within 4 weeks of a viral infection in 46% of patients—a temporal pattern that is consistent with a postviral, idiopathic autonomic neuropathy.

Conclusion: Patients with CFS show alterations in measures of sympathetic and para-sympathetic nervous system function. These results, which provide the physiological basis for the orthostatic intolerance and other symptoms of autonomic function in this patient group, may be explained by cardiovascular deconditioning, a postviral idiopathic autonomic neuropathy, or both.