CHANGES IN DIAPHRAGMATIC EMG ACTIVITY DURING SLEEP IN-SPACE

It remains unknown how increased upper airway resistance (UAR) during sleep could be a function of gravity. We therefore conducted quantitat ive evaluation of the gravitational influence on diaphragmatic EMG act ivity (EMG(di)) in an astronaut to estimate the effect of UAR in space . EMG(di) was recorded by paired surface electrodes on the ground (con trol, C) and aboard a short-term space mission (space, S) for 30 conse cutive h. Mean EMG(di) recorded during quiet breathing in wakefulness was assigned the value of 100. EMG(di) in C was significantly enhanced in all sleep stages compared with that while awake in the supine posi tion (mean +/- SD, 230 +/- 23.2% in non-rapid eye movement (non-REM) S tage II, 233 +/- 13.8 in slow-wave sleep, and 233 +/- 40.0 in REM slee p versus 100 +/- 17.3 in wakefulness, p < 0.001). In contrast, there w as no statistical difference in EMG(di) in S between awake and any non -REM sleep stage (mean +/- SD, 100 +/- 20.5% in wakefulness versus 103 +/- 16.9 in non-REM Stage II and 100 +/- 14.8 in slow-wave sleep; NS) . However, EMG(di) in REM sleep in S was statistically greater (132 +/ - 28.3%) than that during wakefulness or any other sleep stage in spac e (p < 0.001). Therefore, gravity may play a much more significant rol e in the normal healthy human in the increased upper airway resistance during sleep than the relative atonia of the upper airway muscles.