DETECTION OF NONLINEARITY IN THE HEALTHY HEART RHYTHM

Sequences of interbeat intervals from two groups of subjects, 24 in re laxed and 10 in sleeping condition were analyzed by the nonlinear pred ictor method as well as by a method, proposed recently, able to direct ly estimate the time series nonlinearity. The nonlinear predictability of the R-R intervals is tested by using surrogate data. The results o btained with both methods show that nearly all the sequences exhibit a statistically meaningful degree of nonlinearity. This raises the ques tion whether such nonlinearity encodes information about the physiolog ical condition of the examined subjects.