Anomalous behavior of helium and sulfurhexafluoride during single
-breath tests in sustained microgravity.
Prisk, G. Kim, Anne-Marie Lauzon, Sylvia Verbanck, Ann R. Elliott,
Harold J. B. Guy, Manuel Paiva, and John B. West.
Department of Medicine, University of California at San Diego, La
Jolla, CA 92093; and Department of Pneumology AZ-VUB and Biomedical
Physics Laboratory, Universit[acute]e Libre de Bruxelles, Brussels
1070, Belgium.
APStracts 2:0497A, 1995.
We performed single breath wash-in tests for helium and
sulfurhexafluoride in 4 subjects exposed to 14 days of microgravity
([mu]G) during the Spacelab flight SLS-2. Subjects inspired a vital
capacity breath of 5% He, 1.25% SF6,, remainder oxygen, and then
exhaled to residual volume at 0.5 l/sec. The tests were also
performed with a 10 sec breath hold at the end of inspiration.
Measurements were also made with the subjects standing and supine in
1G. Phase III slope was measured after the deadspace washout and
prior to the onset of airway closure. In all subjects in 1G, whether
standing or supine, phase III slope for SF6 was significantly steeper
than that for He. However in [mu]G, the slopes became the same.
Furthermore following breath holding in [mu]G, the SF6 slopes were
significantly flatter than those for He. On return to 1G, the changes
were reversed, and there was no difference between preflight and
postflight values. Because most of the phase III slope reflects
interactions between convective and diffusive transport processes in
the acinar regions of the lung, the results suggest that [mu]G causes
conformational changes in the acini, or changes in cardiogenic mixing
in the lung periphery, but in either case the mechanism is unclear.
Received 22 May 1995; accepted in final form 1 November 1995.
APS Manuscript Number A536-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95