Neurally mediated hypotension & autonomic dysfunction measured by heart rate variability during head-up tilt testing in children with Chronic Fatigue Syndrome (CFS)

Recent investigations suggest a role for neurally mediated

hypotension (NMH) in the symptomatology of chronic fatigue

syndrome (CFS) in adults. Our previous observations in

children with NMH and syncope (S) unrelated to CFS indicate

that the modulation of sympathetic and parasympathetic tone

measured by indices of heart rate variability (HRV) is

abnormal in children who faint during head-up tilt (HUT).

In

order to determine the effects of autonomic tone on HUT in

children with CFS we performed 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 tilted to 80

degrees for 40 minutes or until syncope occurred. Time domain

indices included RR interval, SDNN, RMSSD, and pNN50. An

autoregressive 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 vasodepressor syncope) and

three patients did not (CFS-). Sixteen syncope patients

fainted (S+, all mixed vasodepressor- cardioinhibitory) and 10

did not (S-). Four control patients fainted (Control+, all

mixed vasodepressor-cardioinhibitory) and nine did not

(Control-). Baseline indices of HRV were not different between

Control+ and S+, and between Control- and S-, but were

depressed in S+ compared to S-. HRV indices were strikingly

decreased in CFS patients compared to all other groups. With

tilt, SDNN, RMSSD, and pNN50 and spectral indices decreased in

all groups, remaining much depressed in CFS compared to S or

control subjects. With HUT, sympathovagal indices (LFP/HFP,

nLFP, and nHFP) were relatively unchanged in CFS, which

contrasts with the increase in nLFP with HUT in all other

groups. With syncope RMSSD, SDNN, LFP, TP, and HFP increased

in S+ (and Control+), suggesting enhanced vagal heart rate

regulation. These increases were not observed in CFS+

patients.

CFS is associated with NMH during HUT in children.

All indices of HRV are markedly depressed in CFS patients,

even when compared with already low HRV in S+ or Control+

patients. Sympathovagal balance does not shift toward enhanced

sympathetic modulation of heart rate with HUT and there is

blunting in the overall HRV response with syncope during HUT.

Taken together these data may indicate autonomic impairment in

patients with CFS.

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