Time course of increasing nonlinear properties of heart rate variability after heart transplantation

Heart transplant recipients show remarkable differences in the properties of their heart rate variability (HRV) compared to normal subjects. For eight patients, nonlinear behaviour of HRV is investigated at different dates after surgery. The method used is basically a statistical test procedure that compares the short term predictability of a measured time series of RR-intervals to that of an ensemble of surrogate data. Surrogate data share the same autocorrelation function with the underlaying RR-interval series but are otherwise random. Our results suggest an increasing physiological control of the grafted heart by the autonomous nervous system which is reflected in the p-values of our test procedure.