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

Background Data on the prevalence of orthostatic intolerance (01) in patients with chronic fatigue syndrome (CFS) are limited and controversial. We tested the hypothesis that a majority of CFS patients exhibit 01 during head-up tilt. Methods Hemodynamic and neurohumoral responses to 40 minutes of head-up tilt were studied in 36 CFS patients and 36 healthy controls. Changes in stroke volume, cardiac output and peripheral vascular resistance were estimated from finger arterial pressure waveform analysis (Model-flow). Blood samples were drawn before and at the end of head-up tilt for measurement of plasma catecholamines. Results At baseline, supine heart rate was higher in CFS patients (CFS: 66.4 +/- 8.4 bpm; controls: 57.4 +/- 6.6 bpm; p