Power spectrum analysis of heart rate variability in Guillain-Barré syndrome. A longitudinal study

Power spectrum analysis of heart rate variability was repeatedly carried out on 13 patients with Guillain-Barré syndrome for up to 1 year by Fourier analysis of regular beat-to-beat (R-R) intervals which were recorded for 5 min, converted into a continuous function by linear interpolation and resampled at 5 Hz. Low-frequency (LF) power (reflecting a mixture of parasympathetic and sympathetic activity) and high-frequency (HF) power (reflecting parasympathetic tone) were calculated by integrating the spectra from 0.04 to 0.15 Hz and from 0.15 to 0.4 Hz, respectively. At the height of the disease, the HF component was significantly decreased. The LF:HF ratio, which has been suggested to be an indicator for sympathetic activity, was increased compared with the follow-up value after 1 year. Both measures returned to normal gradually over time. Pooled-data analysis suggested that both HF and LF power were significantly related to the responses of standardized parasympathetic function tests, while the LF:HF ratio was inversely correlated with sympathetic vasomotor activity. In patients presenting with tachycardia, LF and HF power were strikingly decreased compared with patients with normal heart rates, while in patients showing vagal over-reactivity, the power of both spectral bands was significantly increased. The results suggest that spectral analysis of heart rate variability is useful for investigating the cardiovascular neural regulation in patients with Guillain-Barré syndrome. In this disorder, the sympathovagal balance is clearly shifted to sympathetic predominance at the height of the disease.