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1 Biomedical Physics Laboratory, Université Libre de Bruxelles, 1070; 2 Department of Pneumology, Akademisch Ziekenhuis, Vrije Universiteit Brussels, 1090 Brussels, Belgium; 3 European Space Agency, ESTEC, NL-2200 AG Noordwijk, Holland; and 4 Department of Medicine, University of California, San Diego, La Jolla, California 92093-0931
We performed tidal volume single-breath washins (SBW) by using tracers of different diffusivity and varied the time spent in microgravity (µG) before the start of the tests to look for time-dependent effects. SF6 and CH4 phase III slopes decreased by 35 and 26%, respectively, in µG compared with 1 G (P < 0.05), and the slope difference between gases disappeared. There was no effect of time in µG, suggesting that neither the hypergravity period preceding µG nor the time spent in µG affected gas mixing at volumes near functional residual capacity. In previous studies using SF6 and He (Lauzon A-M, Prisk GK, Elliott AR, Verbanck S, Paiva M, and West JB. J Appl Physiol 82: 859-865, 1997), the vital capacity SBW showed an increase in slope difference between gases in transient µG, the opposite of the decrease in sustained µG. In contrast, tidal volume SBW showed a decrease in slope difference in both µG conditions. Because it is only the behavior of the more diffusive gas that differed between maneuvers and µG conditions, we speculate that, in the previous vital capacity SBW, the hypergravity period preceding the test in transient µG provoked conformational changes at low lung volumes near the acinar entrance.
vital capacity single-breath washout; phase III slope; helium; gas mixing; sustained microgravity
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