Sleep at simulated 2438 m: effects on oxygenation, sleep quality, and postsleep performance.

INTRODUCTION Crewmembers on ultra long-range commercial flights have the opportunity for rest and sleep in onboard areas in which the barometric pressure is 75.3 kPa (565 mmHg) or higher, equivalent to a terrestrial altitude of 2438 m (8000 ft) or lower. Sleep at higher altitudes is known to be disturbed, resulting in postsleep neurobehavioral performance decrements. We investigated the effects of sleep at 2438 m on oxygen saturation, heart rate, sleep quantity, sleep quality, postsleep neurobehavioral performance, and mood. METHODS Twenty men, 30-56 yr of age, participated in a blinded cross-over investigation conducted in a hypobaric chamber to compare the effects of sleep at altitude (ALT, 2438 m) and ground level (GND, 305 m). RESULTS SpO2 measured before sleep was significantly lower at ALT than at GND, 90.7 +/- 2.0% (average +/- SD) and 96.2 +/- 2.0%, respectively. During sleep, SpO2 decreased further to 86.1 +/- 2.0% at ALT, and 92.3% +/- 2.0% at GND. The percent of time during which SpO2 was below 90% was 44.4% (3.6-86.9%) at ALT and 0.1% (0.0-22.9%) at GND. Objective and subjective measurements of sleep quantity and quality did not differ significantly with altitude, nor did postsleep neurobehavioral performance or mood. DISCUSSION The absence of significant changes in sleep and post-sleep neurobehavioral performance associated with pronounced oxygen desaturation during sleep was unexpected. Further study is needed to determine if the same effects occur in women and to characterize the changes in respiratory physiology that occur during sleep at 2438 m in both sexes.