A Measure of Heart Rate Variability is Sensitive to Orthostatic Challenge in Women with Chronic Fatigue Syndrome

Abstract

The use of symptoms generated by head up tilt (HUT) is not a useful tool in identifying chronic fatigue syndrome (CFS). We investigated whether heart rate variability (HRV) assessed early during HUT might be useful. A sample of 46 female subjects (24 with CFS and 22 sedentary, age-matched healthy controls; CON) who had exhibited no difference in time to syncope during tilt was examined for HRV responses to 10 min of 70° HUT after 5 min of baseline in the supine position. HRV data were analyzed by the method of coarse graining spectral analysis. Variables compared between groups included mean and standard deviation (SD_RRI) of RR intervals (RRI), amplitudes of low- (A_LF; 0.04–0.15 Hz) and high-frequency (A_HF; >0.15 Hz) harmonic as well as aperiodic, fractal (A_FR; 1/f^β) spectral components, the spectral exponent β, and the difference in these values between baseline and HUT for each subject. In the supine baseline, only mean RRI was significantly (P< 0.01) lower in CFS than in CON. During HUT, however, mean RRI (P < 0.01), SD_RRI, (P < 0.01), A_HF (P < 0.05), and A_FR (P < 0.01) were significantly lower in CFS than in CON. When the difference in values between baseline and HUT for each subject was examined, only the difference for A_FR (ΔA_FR) was significantly (P < 0.01) lower in CFS than in CON, suggesting that A_FR is a disease-specific response of HRV to HUT. When a cut-off level was set to ΔA_FR = –2.7 msec, the sensitivity and the specificity in differentiating CFS from controls were 90% and 72%, respectively. The data suggest that a decrease in aperiodic fractal component of HRV in response to HUT can be used to differentiate patients with CFS from CON.