Change of the heart rate variability components in stroke patients when falling asleep

It is well known that stroke patients often have cardiovascular accidents during sleep. The aim of this study is to investigate the change of the autonomic nervous system function of stroke patients in the transition period from wakefulness to sleep. We studied three different groups, normal young subjects (21.3 ± 0.6 years; n = 20), normal elderly subjects (69.9 ± 1.3 years; n = 16) and stroke patients (72.8 ± 2.5 years; n = 10). An Actiwatch (Mini-mitter Co.) was used to distinguish sleep from wakefulness. An Activetracer AC-301 (ARM electronics) was used to record the R-R interval of an electrocardiogram at a sampling rate of 1 kHz. By applying maximum entropy methods (MemCalc/CHIRAM) to these data, the power spectrum of heart rate variability (HRV) was quantified in the area of two frequency bands: the high frequency (HF) power density component (0.15–0.40 Hz) and the low frequency (LF) power density component (0.04–0.15 Hz). In normal young and elderly subjects, the HF power density component increased significantly from wakefulness to sleep. However, in the stroke patients, there was no such increment. We also found that stroke patients showed no decrease in the LF/HF ratio after falling asleep, which was seen both in the normal young and elderly subjects. The abolishment of parasympathetic dominance during sleep may underlie cardiovascular accidents in stroke patients, such as arrhythmia and sudden death.