Lyapunov exponents calculated from heart rate variability time series

The chaotic deterministic approach is a fascinating and efficient descriptive paradigm for complexity in biological systems. It can explain the organized variability inherent in physiological structure and function. Lyapunov exponents quantify the exponential divergence of trajectories which happens for chaotic systems in state space. Here, the authors compute the positive and the entire spectrum of Lyapunov exponents. They present the results obtained on time series from classical chaotic attractors, like the Henon map and the Rossler system as well as on experimental time series derived from the heart rate variability (HRV) signal. The HRV time series considered refer to normal subjects and to patients with cardiovascular diseases. It is concluded that the chaotic characteristics of the cardiovascular regulation system seem to be confirmed