A PROGRAM FOR THE USER-INDEPENDENT COMPUTATION OF THE CORRELATION DIMENSION AND THE LARGEST LYAPUNOV EXPONENT OF HEART-RATE DYNAMICS FROM SMALL DATA SETS

We propose a specially optimized computer program for the user-indepen dent calculation of the correlation dimension D and the largest Lyapun ov exponent L of heart rate dynamics on the basis of only 1024 electro cardiographically recorded RR intervals (heartbeat intervals). The val idity of our program was established by analyzing a set of artificial standard signals. Our norm values of the correlation dimension (D = 5. 37 +/- 0.62) and the largest Lyapunov exponent (L = 0.561 +/- 0.037 bi ts/beat) of RR dynamics, obtained from 79 healthy adults aged 26.3 +/- 4.8 years, were independent of gender and age; D and L correlated sli ghtly with each other (Pearson correlation coefficient r = 0.26). Shor tterm reliability, tested for 25 of our subjects by two successive rec ordings, was fair: the intraclass correlation coefficients (ICCs) were 0.45 and 0.41 for D and L of RR dynamics, respectively. However, long -term reliability, tested for eight of our subjects by ten weekly reco rdings, was acceptable for L (ICC = 0.40) but not for D (ICC = 0.01). These results permit group comparisons on the basis of single measurem ents of L of RR dynamics. A reliable differentiation between young hea lthy individuals requires four measurements of L.