On the fractal nature of heart rate variability in humans: effects
of vagal blockade.
Yamamoto, Yoshiharu, Yoshio Nakamura, Hiroshi Sato, Machiko Yamamoto,
Kazuo Kato, and Richard L. Hughson.
Laboratory for Exercise Physiology and Biomechanics, Faculty of
Education, The University of Tokyo, 731 Hongo, Bunkyo-ku, Tokyo 113,
Japan, Department of Sports Sciences, School of Human Sciences,
Waseda University, 257915 Mikashima, Tokorozawa, Saitama 359, Japan,
The Cardiovascular Institute, 7310 Roppongi, Minato-ku, Tokyo 106,
Japan and Department of Kinesiology, Faculty of Applied Health
Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1,
Canada.
APStracts 2:0032R, 1995.
The purpose of the present study was to investigate the effects of the
vagal blocker atropine on the fractal nature of human heart rate
variability (HRV) at rest. Approximately ten- minute segments of
beat-to-beat heartbeat intervals, i.e. HRV, of ten normal subjects
and eleven cardiac disease patients were measured before and after
intravenous injection of 0.5 0.75 mg atropine sulfate. HRV data were
analyzed by coarse graining spectral analysis (Yamamoto, Y., and R.L.
Hughson, Physica 68D: 250 264, 1993) to break down their total power
into harmonic and nonharmonic (fractal) components. The harmonic
component was used to calculate the contribution of high (> 0.15 Hz)
frequency components to total HRV power (%HF). From the fractal
component, the contribution of the fractal component to total HRV
power (%Fractal), the spectral exponent b, and Hurst scaling exponent
(H) were calculated. For both normal subjects and cardiac patients,
atropine resulted in significantly (P < 0.05) less mean HRV and
significantly (P < 0.05) greater b as compared to control, while mean
values for %Fractal were as high as 70 % and were not significantly
(P > 0.05) different between atropine and control. The mean value of
H with atropine was significantly (P < 0.05) greater than that for
control. Directional changes in %HF and the spectral exponent b were
consistent with only one exception for a patient who had the smallest
change in log %HF by atropine. The normally irregular, fractal,
pattern of resting HRV was decreased by atropine as shown by the
decrease in %HF and the increase in b. These results suggested that
the fractal components of resting HRV in humans were mediated via
cardiac parasympathetic neural activity.
Received 10 June 1994; accepted in final form 27 January 1995.
APS Manuscript Number R319-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 February 1995.