The visibility graph analysis of heart rate variability during chi meditation and Kundalini Yoga techniques

The human heartbeat reflects one of the most crucial types of complex physiologic fluctuations. The purpose of this study is to study and evaluate the complexity of heart rate time series to capture its intrinsic multiscale dynamics based on the concept of fractality and complexity. The visibility graph (VG) of the heart rate series is proposed as a quantitative method to differentiate subjects in rest and meditation periods of two techniques: Chi meditation and Kundalini Yoga meditation. Differential complexities between the two mentioned states are quantified using the power of scale-freeness (PS) and the graph index complexity (GIC) in VG. The model is applied to available heart rate signals in the PhysioBank. The results reveal the promising ability of PS and GIC to assess the distinction between the two states. However, in both meditation techniques, the complexities of heart rate signals are increased during meditation. The results also show all heart rate series have visibility graphs with a power-law topology, and fractality in the heart rate series is dictated by a mechanism associated with the chaotic nature of the biological signals that could be useful to evaluate heart rate signals during meditation.