We propose a model for heart rate variability (HRV) of a healthy individual during sleep with the assumption that the heart rate variability is predominantly a random process. Autonomic nervous system activity has different properties during different sleep stages, and this affects many physiological systems including the cardiovascular system. Different properties of HRV can be observed during each particular sleep stage. We believe that taking into account the sleep architecture is crucial for modeling the human nighttime HRV. The stochastic model of HRV introduced by Kantelhardt et al. was used as the initial starting point. We studied the statistical properties of sleep in healthy adults, analyzing 30 polysomnographic recordings, which provided realistic information about sleep architecture. Next, we generated synthetic hypnograms and included them in the modeling of nighttime RR interval series. The results of standard HRV linear analysis and of nonlinear analysis (Shannon entropy, Poincaré plots, and multiscale multifractal analysis) show that—in comparison with real data—the HRV signals obtained from our model have very similar properties, in particular including the multifractal characteristics at different time scales. The model described in this paper is discussed in the context of normal sleep. However, its construction is such that it should allow to model heart rate variability in sleep disorders. This possibility is briefly discussed.

ACKNOWLEDGMENTS

We would like to thank our colleagues from the Cardiovascular Physics Group at the Faculty of Physics of Warsaw University of Technology for support. Special thanks go to Gari Clifford from Emory University and Georgia Institute of Technology for sharing uploaded version of HRV model by McSharry and Clifford.

We also thank for providing the medical data the following physicians: Rafał Baranowski, Aleksander Prejbisz, Marek Kabat, and Andrzej Januszewicz from The Cardinal Stefan Wyszyński Institute of Cardiology, Warsaw, Poland, and Anna Piotrowska and Waldemar Szelenberg from the Faculty of Psychiatry, Warsaw University of Medicine, Poland.