Cardiac interbeat interval dynamics from childhood to senescence - Comparison of conventional and new measures based on fractals and chaos theory

Background-New methods of R-R interval variability based on fractal scaling and nonlinear dynamics ("chaos theory") may give new insights into heart r ate dynamics. The aims of this study were to (1) systematically characteriz e and quantify the effects of aging from early childhood to advanced age on 24-hour heart rate dynamics in healthy subjects; (2) compare age-related c hanges in conventional time- and frequency-domain measures with changes in newly derived measures based on fractal scaling and complexity (chaos) theo ry; and (3) further test the hypothesis that there is loss of complexity an d altered fractal scaling of heart rate dynamics with advanced age. Methods and Results-The relationship between age and cardiac interbeat (R-R ) interval dynamics from childhood to senescence was studied in 114 healthy subjects (age range, 1 to 82 years) by measurement of the slope, beta, of the power-law regression line (log power-log frequency) of R-R interval var iability (10(-4) to 10(-2) Hz), approximate entropy (ApEn), short-term (alp ha(1)) and intermediate-term (alpha(2)) fractal scaling exponents obtained by detrended fluctuation analysis, and traditional time- and frequency-doma in measures from 24-hour ECG recordings. Compared with young adults (<40 ye ars old, n=29), children (<15 years old, n=27) showed similar complexity (A pEn) and fractal correlation properties (alpha(1), alpha(2), beta) of R-R i nterval dynamics despite lower spectral and time-domain measures, Progressi ve loss of complexity (decreased ApEn, r=-0.69, P<0.001) and alterations of long-term fractal-like heart rate behavior (increased alpha(2), r=0.63, de creased beta, r=-0.60, P<0.001 for both) were observed thereafter from midd le age (40 to 60 years, n=29) to old age (>60 years, n=29). Conclusions-Cardiac interbeat interval dynamics change markedly from childh ood to old age in healthy subjects. Children show complexity and fractal co rrelation properties of R-R interval time series comparable to those of you ng adults, despite lower overall heart rate variability. Healthy aging is a ssociated with R-R interval dynamics showing higher regularity and altered fractal scaling consistent with a loss of complex variability.