Cross-correlation between 1/f-like fluctuations in heartbeat and diurnal changes in the sleep-waking stage

The cross-correlation function between diurnal changes in 1/f-like fluctuations of the R-R interval and those of the sleep-waking stage was calculated based on the data from six normal subjects in order to investigate the interactions among circadian components. Sleep stage was scored according to the standard criteria and waking stage was scored with criteria developed for the present study. Polysomnography was performed for 11 h during the daytime. The equation for 1/f was approximated using the power spectra of the R-R interval every 10 min. Cross-correlation analysis between sleep-waking stage and 1/f fluctuation of the R-R interval suggested that the neural network for 1/f fluctuation in heartbeat is influenced by the sleep-wake cycle with a time lag in the order of tens of minutes.