NEURALLY-MEDIATED HYPOTENSION AND AUTONOMIC DYSFUNCTION MEASURED BY HEART-RATE-VARIABILITY DURING HEAD-UP TILT TESTING IN CHILDREN WITH CHRONIC-FATIGUE-SYNDROME

Recent investigations suggest a role for neurally mediated hypotension (NMH) in the symptomatology of chronic fatigue syndrome (CFS) in adul ts. Our previous observations in children with NMH and syncope (S) unr elated to CFS indicate that the modulation of sympathetic and parasymp athetic tone measured by indices of heart rate variability (HRV) is ab normal in children who faint during head-up tilt (HUT). In order to de termine the effects of autonomic tone on HUT in children with CFS we p erformed measurements of HRV during HUT in 16 patients aged 11-19 with CFS. Data were compared to 26 patients evaluated for syncope and with 13 normal control subjects. After 30 minutes supine, patients were ti lted to 80 degrees for 40 minutes or until syncope occurred. Time doma in indices included RR interval, SDNN, RMSSD, and pNN50. An autoregres sive model was used to calculate power spectra. LFP (.04-.15 Hz), HFP (.15-.40Hz), and TP (.01-.40Hz). Data were obtained supine (baseline) and after HUT. Thirteen CFS patients fainted (CFS+, 5/13 pure vasodepr essor syncope) and three patients did not (CFS-). Sixteen syncope pati ents fainted (Sf, all mixed vasodepressor-cardioinhibitory) and 10 did not (S-). Four control patients fainted (Control+, all mixed vasodepr essor-cardioinhibitory) and nine did not (Control-). Baseline indices of HRV were not different between Control+ and Sf, and between Control - and S-, but were depressed in S+ compared to S-. HRV indices were st rikingly decreased in CFS patients compared to all other groups. With tilt, SDNN, RMSSD, and pNN50 and spectral indices decreased in all gro ups, remaining much depressed in CFS compared to S or control subjects . With HUT, sympathovagal indices (LFP/HFP, nLFP, and nHFP) were relat ively unchanged in CFS, which contrasts with the increase in nLFP with HUT in all other groups. With syncope RMSSD, SDNN, LFP, TP, and HFP i ncreased in S+ (and Control+), suggesting enhanced vagal heart rate re gulation. These increases were not observed in CFS+ patients. CFS is a ssociated with NMH during HUT in children. All indices of HRV are mark edly depressed in CFS patients, even when compared with already low HR V in S+ or Control+ patients. Sympathovagal balance does not shift tow ard enhanced sympathetic modulation of heart rate with HUT and there i s blunting in the overall HRV response with syncope during HUT. Taken together these data may indicate autonomic impairment in patients with CFS.