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Vol. 84, Issue 2, 661-668, February 1998
Department of Medicine, University of California San Diego, La Jolla, California 92093; and Biomedical Physics Laboratory, Université Libre de Bruxelles, Brussels 1070, Belgium
Lauzon, Anne-Marie, Ann R. Elliott, Manuel Paiva, John B. West, and G. Kim Prisk. Cardiogenic oscillation phase
relationships during single-breath tests performed in
microgravity. J. Appl. Physiol. 84(2):
661-668, 1998.
We studied the phase relationships of the
cardiogenic oscillations in the phase III portion of single-breath washouts (SBW) in normal gravity (1 G) and in sustained microgravity (µG). The SBW consisted of a vital capacity inspiration of 5% He-1.25% sulfurhexafluoride-balance
O2, preceded at residual volume by
a 150-ml Ar bolus. Pairs of gas signals, all of which still showed
cardiogenic oscillations, were cross-correlated, and their phase
difference was expressed as an angle. Phase relationships between
inspired gases (e.g., He) and resident gas
(N2) showed no change from 1 G
(211 ± 9°) to µG (163 ± 7°). Ar bolus and He were
unaltered between 1 G (173 ± 15°) and µG (211 ± 25°),
showing that airway closure in µG remains in regions of high specific ventilation and suggesting that airway closure results from lung regions reaching low regional volume near residual volume. In contrast,
CO2 reversed phase with He between
1 G (332 ± 6°) and µG (263 ± 27°), strongly
suggesting that, in µG, areas of high ventilation are associated with
high ventilation-perfusion ratio (
A/
).
This widening of the range of
A/
in µG may explain previous measurements (G. K. Prisk, A. R. Elliott,
H. J. B. Guy, J. M. Kosonen, and J. B. West. J. Appl.
Physiol. 79: 1290-1298, 1995) of an overall
unaltered range of
A/
in µG, despite more homogeneous distributions of both ventilation and
perfusion.
ventilation distribution; perfusion distribution; gas exchange; cross-correlation coefficient; helium; sulfurhexafluoride; argon
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