Nonlinear dynamics in HRV signals after heart transplantations

The time course of heart rate variability registered from heart transplant recipients is investigated using three different approaches for possible detection of nonlinear dynamics. The three methods used are the Lyapunov exponents, the correlation dimension, and the nonlinear prediction approach. Comparisons of the results of the three approaches revealed that the Lyapunov exponent does not yield any indication of changes in nonlinear dynamics. Whereas, the other two methods support the conclusion previously reported that HRV signals tend to show chaotic behavior as the time increases after the heart transplantation