DEMONSTRATION OF NONLINEAR COMPONENTS IN HEART-RATE-VARIABILITY OF HEALTHY-PERSONS

We present a systematic approach for detecting nonlinear components in heart rate variability (HRV). The analysis is based on twenty;three 4 8-h Holter recordings in healthy persons during sinus rhythm. Although many segments of 1,024 R-R intervals are stationary, only few station ary segments of 8,192-32,768 R-R intervals can be found using a test o f Isliker and Kurths (Int. J. Bifurcation Chaos 3:1573-1579, 1993.). B y comparing the correlation integrals from these segments and correspo nding surrogate data sets, we reject the null hypothesis that these ti me series are realization of linear processes. On the basis of a test statistic exploring the differences of consecutive R-R intervals, we r eject the hypothesis that the R-R intervals represent a static transfo rmation of a linear process using optimized surrogate data. Furthermor e, time irreversibility of the heartbeat data is demonstrated. We inte rpret these results as a strong evidence for nonlinear components in H RV. Thus R-R intervals from healthy persons contain more information t han can be extracted by linear analysis in the time and frequency doma in.