Nonlinear instabilities and nonstationarity in human heart-rate variability

The human cardiovascular system exhibits complex and interesting dynamics, including heart-rate fluctuations. The heart rate fluctuates irregularly - a phenomenon called heart-rate variability. Here, we present a short review of our experience with the analysis of heart-rate variability. Initially, we focused on the assessment of the risk of sudden cardiac death due to cardiac arrest. During this research, we became aware of intermittency in heart-rate variability. We identify the intermittency as type I and describe how simple models helped us understand the differences between our results and textbook properties of this phenomenon. We also mention the use of modified van der Pol oscillators for the modeling of heart-rate variability. Finally, we review our latest research on the modeling of the heart tissue´s properties using the true shape of the ventricles reconstructed from clinical electro-physiological measurement data.