Characterization of Sleep Stages by Correlations of Heartbeat Increments
Abstract
We study correlation properties of the magnitude (volatility) and the sign (direction) of the heartbeat increments in light sleep, deep sleep, and REM sleep. Using the detrended fluctuation analysis (DFA) method, we find short-range anticorrelations in the signs of the increments. These anticorrelations are most pronounced in deep sleep, weaker in light sleep and even more weak in REM sleep. In contrast, the magnitudes of the increments are long-range correlated during REM sleep and uncorrelated during deep sleep. Our findings suggest that the nonlinear contribution of heartbeat regulation could be more pronounced during REM sleep than during deep sleep, and raise the possibility of detecting sleep stages ("brain activity") using only cardiogram records ("heart activity").Keywords
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