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Am. J. Respir. Crit. Care Med., Volume 164, Number 3, August 2001, 478-485

Microgravity Reduces Sleep-disordered Breathing in Humans

ANN. R. ELLIOTT, STEVEN A. SHEA, DERK-JAN DIJK, JAMES K. WYATT, EYMARD RIEL, DAVID F. NERI, CHARLES A. CZEISLER, JOHN B. WEST, and G. KIM PRISK

Department of Medicine, University of California, San Diego, La Jolla, California; Circadian, Neuroendocrine and Sleep Disorders Section, Division of Endocrinology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts; and NASA Ames Research Center, Mountain View, California

To understand the factors that alter sleep quality in space, we studied the effect of spaceflight on sleep-disordered breathing. We analyzed 77 8-h, full polysomnographic recordings (PSGs) from five healthy subjects before spaceflight, on four occasions per subject during either a 16- or 9-d space shuttle mission and shortly after return to earth. Microgravity was associated with a 55% reduction in the apnea-hypopnea index (AHI), which decreased from a preflight value of 8.3 ± 1.6 to 3.4 ± 0.8 events/h inflight. This reduction in AHI was accompanied by a virtual elimination of snoring, which fell from 16.5 ± 3.0% of total sleep time preflight to 0.7 ± 0.5% inflight. Electroencephalogram (EEG) arousals also decreased in microgravity (by 19%), and this decrease was almost entirely a consequence of the reduction in respiratory-related arousals, which fell from 5.5 ± 1.2 arousals/h preflight to 1.8 ± 0.6 inflight. Postflight there was a return to near or slightly above preflight levels in these variables. We conclude that sleep quality during spaceflight is not degraded by sleep-disordered breathing. This is the first direct demonstration that gravity plays a dominant role in the generation of apneas, hypopneas, and snoring in healthy subjects.

Keywords: obstructive sleep apnea; airway collapse; arousals; gravitational effect




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