Estimation of the largest Lyapunov exponent of an RR interval and its use as an indicator of decreased autonomic heart rate control

Recent evidence points to a decrease in autonomic control of heart rate in same states of disease. It has been shown that interbeat intervals are not random but exhibit short range correlations governed by deterministic laws. Lyapunov exponents, which provide a qualitative and quantitative characterization of dynamical behaviour, are related to the exponentially fast divergence or convergence of nearby orbits in phase space. A system with one or more positive Lyapunov exponents is defined to be chaotic. In this study, the phase portraits from ECG recordings have been reconstructed, and the Lyapunov exponents are estimated. The authors examine the diagnostic value of the Lyapunov exponent as an indicator of decreased autonomic control of heart rate