Estimation of sleep onset latency based on the correlation between blood pressure and heart beat interval

Sleep onset latency (SOL) provides an objective assessment of sleepiness and it also clinically useful as a sleep deprivation diagnostic tool. In this study, we suggest a new approach to estimate SOL based on the correlation between blood pressure (BP) and heart beat interval (HBI). This approach facilitates less intrusive finding of SOL as compared with currently using polysomnographic method. We hypothesized that the arterial baroreflex, one kind of reflex mechanism to regulate BP, takes a role of maintaining sleep's toning-down effect on BP. At the time of transition from full wakefulness to sleep, the toning-down effect starts to drop the BP and the arterial baroreflex is activated to maintain lowered BP by leading to increase in HBI for the elevated BP. Consequently, there is a great contribution of arterial baroreflex to HBI control. With a quantitative evaluation of the contribution, we tried to estimate SOL. For six healthy subjects (27.5 ± 3.15 years), the mean absolute error (MAE) was 0.3 ± 0.42 minutes. We expect our method can be applicable to non-intrusive and automatic SOL estimation system by not using electroencephalogram (EEG) sensors.