Sleep Stage Dependence of Invariance Characteristics in Fluctuations of Healthy Human Heart Rate

Abstract

The outstanding feature of healthy human heart rate is the robust scale invariance in the non‐Gaussian probability density function (PDF), which is preserved not only in a quiescent condition, but also in a dynamic state during waking hours [K. Kiyono et al. Phys. Rev. Lett. 93 (2004)]. Together with 1/f like scaling, this characteristic is a strong indication of far‐from‐equilibrium, critical‐like dynamics of heart rate regulation. Our results suggest that healthy human heart rate departs from a critical state‐like operation during sleeping hours, at a rate which is heterogeneous with respect to sleep stages annotated according to traditional techniques. We study specific contributions of sleep stages to the relative departure from criticality through the analysis of sleep stage dependence of the root mean square of multiscale local energy and the multiscale PDF. There is a possibility that the involvement of cortical activity may be important for a critical state‐like operation.