Forced expirations and maximum expiratory flow-volume curves during
sustained microgravity on spacelab sls-1.
Elliott, Ann R., G. Kim Prisk, Harold J. B. Guy, Janelle M. Kosonen,
and John B. West.
Department of Medicine, University of California, San Diego, La
Jolla, CA 92093-0931
APStracts 2:0542A, 1995.
Gravity is known to influence the mechanical behavior of the lung and
chest wall. However, the effect of sustained microgravity ([mu]G) on
forced expirations has not previously been reported. Tests were
carried out by four subjects in both the standing and supine posture
during each of the 7 preflight and 4 postflight data collection
sessions, and 4 times during the 9 days of [mu]G exposure on Spacelab
SLS-1. Compared to preflight standing values, peak expiratory flow
rate (PEFR) was significantly reduced by 12.5% on flight day 2 (FD2),
11.6% on FD4, and by 5.0% on FD5, but returned to standing values by
FD9. The supine posture caused a 9% reduction in PEFR. Forced vital
capacity (FVC) and forced expired volume in 1 second (FEV1) were
slightly reduced (3-4%) on FD2 but returned to preflight standing
values on FD4 and 5, and by FD9 both were slightly but significantly
greater than standing values. FVC and FEV1 were both reduced in the
supine posture (8-10%). Forced expiratory flow at 50% of vital
capacity (VC) and between 25 and 75% of VC (FEF50% and FEF25-75%) did
not change during [mu]G, but were reduced in the supine posture.
Analysis of the maximum expiratory flow-volume (MEFV) curve showed
that [mu]G caused no consistent change in the curve configuration
when individual inflight days were compared to preflight standing
curves, although two subjects did show a slight reduction in flows at
low lung volumes from FD2 to FD9. The interpretation of the lack of
change in curve configuration must be made cautiously since the lung
volumes varied from day to day inflight. Therefore the flows at
absolute lung volumes in [mu]G and preflight standing are not being
compared. The supine curves showed a subtle but consistent reduction
in flows at low lung volumes. The mechanism responsible for the
reduction in PEFR is not clear. It could be due to a lack of physical
stabilization when performing the maneuver in the absence of gravity,
or a transient reduction in respiratory muscle strength.
Received 23 December 1994; accepted in final form 30 November
1995.
APS Manuscript Number A1312-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 12 December 95