Age-related alterations in the fractal scaling of cardiac interbeat
interval dynamics.
Iyengar, Nikhil.
C. K. Peng, Raymond Morin, Ary L. Goldberger, Lewis A. Lipsitz
APStracts 3:0175R, 1996.
We postulated that aging is associated with disruption in the fractal
-like long-range correlations that characterize healthy sinus rhythm
cardiac interval dynamics. Ten young (21-34 years) and 10 elderly
(68-81 years) rigorously screened healthy subjects underwent 120
minutes of continuous supine resting electrocardiographic recording.
We analyzed the interbeat interval time series using standard time
and frequency domain statistics, and using a fractal measure --
detrended fluctuation analysis--to quantify long-range correlation
properties. In healthy young subjects, interbeat intervals
demonstrated fractal scaling, with scaling exponents ([alpha]) from
the fluctuation analysis close to a value of 1.0. In the group of
healthy elderly subjects the interbeat interval time series had two
scaling regions. Over the short range, interbeat interval
fluctuations resembled a random walk process (Brownian noise,
[alpha]=1.5), while over the longer range they resembled white noise
([alpha]=0.5). Short ([alpha]s) and long-range ([alpha] l ) scaling
exponents were significantly different in the elderly subjects
compared to young ([alpha]s=1.12+0.19 vs 0.90+0.14, respectively,
p=0.009; [alpha]l=0.75+0.17 vs 0.99+0.10, respectively, p=0.002). The
crossover behavior from one scaling region to another could be
modelled as a first-order autoregressive process, which closely fit
the data from four elderly subjects. This implies that a single
characteristic time scale may be dominating heartbeat control in
these subjects. The age-related loss of fractal organization in
heartbeat dynamics may reflect the degradation of integrated
physiologic regulatory systems, and may impair an individual's
ability to adapt to stress.
Received 12 February 1996; accepted in final form 22 February
1996.
APS Manuscript Number R92-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96