title: A program for the user-independent computation of the correlation dimension and the largest Lyapunov exponent of heart rate dynamics from small data sets.
abstract: We propose a specially optimized computer program for the user-independent calculation of the correlation dimension D and the largest Lyapunov exponent L of heart rate dynamics on the basis of only 1024 electrocardiographically recorded RR intervals (heartbeat intervals). The validity 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 bits/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 slightly with each other (Pearson correlation coefficient r = 0.26). Short-term reliability, tested for 25 of our subjects by two successive recordings, 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 recordings, was acceptable for L (ICC = 0.40) but not for D (ICC = 0.01). These results permit group comparisons on the basis of single measurements of L of RR dynamics. A reliable differentiation between young healthy individuals requires four measurements of L.
authors.affiliation: Institute für Medizinische Psychologie, Universitätsklinikum Essen, Germany.
authors.forename: R E
authors.initials: RE
authors.lastname: Ganz
authors.forename: C
authors.initials: C
authors.lastname: Lenz
mesh_terms: D000328:Adult; D000465:Algorithms; D015982:Bias; D003627:Data Interpretation, Statistical; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D012986:Software Validation; D014584:User-Computer Interface