AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 1 141-R147, Copyright © 1992 by American Physiological Society
Fractal properties in fetal breathing dynamics
H. H. Szeto, P. Y. Cheng, J. A. Decena, Y. Cheng, D. L. Wu and G. Dwyer
Department of Pharmacology, Cornell University Medical College, New York, New York 10021.
The dynamic pattern of fetal breathing was studied in 17 fetal lambs with
chronically implanted electromyographic electrodes in the diaphragm. The
instantaneous breathing rate time series appeared similar on different time
scales, with clusters of faster breathing rates interspersed with periods
of relative quiescience, suggesting self-similarity. Distribution
histograms of the interbreath intervals (IBIs) showed log-normal
distribution for IBIs less than 1 s and inverse power-law distribution for
IBIs greater than 1 s. The ratio of log-normal distribution to power-law
distribution varied from approximately 2 at 102 days to approximately 30 by
130 days of gestation. Fast Fourier transform of the breathing rate time
series revealed 1/f beta power spectra for all animals, with beta
increasing linearly from 0.43 to 0.88 between 102 and 139 days. Studies in
the newborn lamb showed further maturation in both the distribution
characteristics of the IBIs, as well as in the 1/f power spectra, with beta
approaching 1.0 at 2 days after birth. The inverse power-law relationship
in the distribution of the IBIs, together with the 1/f beta power spectra,
indicate scale invariance and suggest that fractal mechanisms are involved
in the regulation of fetal breathing.
