Increased gravitational stress does not alter maximum expiratory flow.
We measured maximum expiratory flow-volume (MEFV) curves in six seated subjects during normal (+1 Gz) and increased (+2 and +3 Gz) gravitational stress. Full MEFV curves, initiated at total lung capacity, were recorded, as were partial MEFV curves, initiated at approximately 60% of the vital capacity. Data were acquired in all subjects breathing air at +1 and +2 Gz; results were available for three subjects breathing 80% He-20% O2 at +1 and +2 Gz, and in two subjects, results were obtained at +3 Gz. Changes in gravitational stress were not associated with changes of either full or partial MEFV curves. The known increase in differences of regional lung volume and recoil caused by increased gravitational stress did not influence maximum expiratory flow. Though increased gravitational stress probably changed regional emptying sequences little during full MEFV maneuvers, substantial changes of emptying sequence were expected during partial maneuvers. It is possible that such changes in emptying sequence occurred but were not associated with changes in maximum flow because the latter was determined by choking in central airways common to all regions.
D000328:Adult; D005540:Forced Expiratory Flow Rates; D006112:Gravitation; D006801:Humans; D008449:Maximal Expiratory Flow-Volume Curves; D008875:Middle Aged; D010827:Physiology / Q000295:instrumentation; D013312:Stress, Physiological / Q000503:physiopathology*