Chaotic behavior from a human biological signal

In this work we study the dynamical behavior of a time series obtained from human biological signals. The data were acquired by monitoring the cardiac signal of a healthy human. We used time-delay coordinates to reconstruct the underlying attractor associated with the cardiac signal. Such a reconstruction showed a toroidal-like attractor with chaotic behavior. A quantitative characterization of such an attractor was carried out via the calculation of the maximal Lyapunov exponent. It is shown that for a large set of data the maximal Lyapunov exponent attains a stationary positive value, which can be interpreted as evidence for the chaotic behavior of the cardiac signal.