Transitions in physiological coupling between heartbeat and pulse across sleep stages

OBJECTIVE: The aim of this study is to investigate the coupling behavior between heartbeat and pulse of blood flow at different sleep stages, and to explore the feasibility of using this coupling strength for automatic sleep staging. APPROACH: The electrocardiogram and photoplethysmography signals are recorded during sleep, and R-wave-to-R-wave intervals (RRI) and pulse-to-pulse intervals (PPI) are extracted respectively. The detrended cross-correlation analysis (DCCA) is applied to quantify long-range cross correlations between the RRIs and PPIs across sleep stages. The DCCA scaling exponents are used as the indicator of coupling strength between heartbeat and pulse, and are compared with detrended fluctuation analysis (DFA) scaling exponents of RRIs and PPIs in the application of sleep stage discrimination. MAIN RESULTS: We find the DCCA scaling exponents between RRIs and PPIs decrease monotonously from wake, REM sleep to light and deep sleep, indicating that the coupling strength between heartbeat and pulse are reduced gradually when entering deep sleep. Statistical analysis shows that the DCCA scaling exponents possess better discrimination ability between wake/REM sleep and light/deep sleep, compared with DFA scaling exponents of RRIs and PPIs. SIGNIFICANCE: Our study reveals the coupling strength between heartbeat and pulse changes regularly across sleep stages, which may help understand the regulation mechanism underlying the cardiovascular system. The DCCA scaling exponents between RRIs and PPIs can be used as an indicator for measuring vigilance level and automatic sleep staging.