Components of the heart rhythm power spectrum in wakefulness and individual sleep stages.

Contributions by 3 major spontaneous oscillatory heart rhythm (HR) components have been analyzed in 20 healthy subjects and 75 ischemic heart disease (IHD) patients during wakefulness and individual sleep stages. Stages of sleep were scored manually based on polygraphic recording of EEG, EOG and EMG throughout the night. HR was fed into the computer continuously for evaluation of the contributions by high- (HFC), medium- (MFC), and low- (LFC) -frequency components to the HR power spectrum. In the healthy subjects, relative contributions by the oscillatory components did not differ during wakefulness, but HFC and LFC prevailed during deep sleep and during REM sleep, respectively. The sleep-mediated changes were related with a more marked decrease in LFC and MFC during deep sleep and an increase during REM sleep as compared with HFC changes. The lower total HR variability in the IHD patients during wakefulness and individual sleep stages was paralleled by a relative increase in LFC whose values were dependent upon the functional state of the IHD patients. The differences in relative contributions by the HR oscillatory components in the IHD patients were related to a more marked decrease in the share of HFC and MFC in the patients as compared with the healthy subjects.