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Vol. 84, Issue 1, 244-252, January 1998
Department of Medicine, University of California, San Diego, La Jolla, California 92093; Akademisch Ziekenhuis, Vrije Universiteit Brussel, 1090 Brussels; and Biomedical Physics Laboratory, Université Libre de Bruxelles, 1070 Brussels, Belgium
Prisk, G. Kim, Ann R. Elliott, Harold J. B. Guy, Sylvia
Verbanck, Manuel Paiva, and John B. West. Multiple-breath washin of helium and sulfur hexafluoride in sustained microgravity.
J. Appl. Physiol. 84(1): 244-252, 1998.
We performed multiple-breath washouts of
N2 and simultaneous washins of He
and SF6 with fixed tidal volume
(~1,250 ml) and preinspiratory lung volume (approximately the
subject's functional residual capacity in the standing position) in
four normal subjects (mean age 40 yr) standing and supine in normal
gravity (1 G) and during exposure to sustained microgravity (µG). The
primary objective was to examine the influence of diffusive processes
on the residual, nongravitational ventilatory inhomogeneity in the lung
in µG. We calculated several indexes of convective ventilatory
inhomogeneity from each gas species. A normal degree of ventilatory
inhomogeneity was seen in the standing position at 1 G that was largely
unaltered in the supine position. When we compared the standing
position in 1 G with µG, there were reductions in phase III slope in
all gases, consistent with a reduction in convection-dependent
inhomogeneity in the lung in µG, although considerable convective
inhomogeneity persisted in µG. The reductions in the indexes of
convection-dependent inhomogeneity were greater for He than for
SF6, suggesting that the distances
between remaining nonuniformly ventilated compartments in µG were
short enough for diffusion of He to be an effective mechanism to reduce
gas concentration differences between them.
humans; spaceflight; zero gravity; distribution of pulmonary ventilation; phase III of expiration; specific ventilation; intra-acinar inhomogeneity; convective inhomogeneity
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