On the fractal nature of heart rate variability in humans: effects
of respiratory sinus arrhythmia.
Yamamoto, Yoshiharu, Jacques-Olivier Fortrat, and Richard L. Hughson.
Laboratory for Exercise Physiology and Biomechanics, Faculty of
Education, The University of Tokyo, 731 Hongo, Bunkyo-ku, Tokyo 113,
Japan, and Department of Kinesiology, Faculty of Applied Health
Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1,
Canada.
APStracts 2:0159H, 1995.
The purpose of the present study was to investigate the basic fractal
nature of the variability in resting heart rate (HRV), relative to
that in breathing frequency (BFV) and tidal volume (TVV), and to test
the hypothesis that fractal HRV is due to the fractal BFV and/or TVV
in humans. In addition, the possible fractal nature of respiratory
volume curves (RVC) and HRV was observed. In the first study, eight
subjects were tested while they sat quietly in a comfortable chair
for 60 min. Beat-to-beat R-R intervals, i.e. HRV, and breath-by
-breath BFV and TVV were measured. In the second study, six subjects
were tested while they were in the supine position for 20 30 min. The
RVC was monitored continuously together with HRV. Coarse graining
spectral analysis (Yamamoto, Y., and R.L. Hughson, Physica D 68: 250
264, 1993) was applied to these signals to evaluate the percentage of
random fractal components in the time series (%Fractal) and the
spectral exponent b which characterizes irregularity of the signals.
The estimates of b were determined for each variable only over the
range normally used to evaluate HRV. Values for %Fractal and b of
both BFV and TVV were significantly (P < 0.05) greater than those
for HRV. In addition, there was no significant (P > 0.05)
correlation between the b values of HRV relative to either BFV (r =
0.14) or TVV (r = 0.34). RVC showed a smooth oscillation as compared
with HRV; %Fractal for RVC (42.3 21.7 %, mean SD) was significantly
(P < 0.05) lower than that for HRV (78.5 4.2 %). The %Fractal
values in high frequency (> 0.15 Hz) bands were also significantly
(P < 0.05) lower for RVC than for HRV. These results indicated that
fractal components of HRV were probably not due to the respiratory
modulation of heart rate.
Received 10 June 1994; accepted in final form 28 February 1995.
APS Manuscript Number H520-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 2 May 1995.