Ambulatory sleep–wake recording in an acclimatized mountaineer over 8 days at high altitude

Continuous ambulatory polygraphy (electroencephalogram and electrooculogram) was recorded on a 34-year-old female mountaineer acclimatized to an altitude of 5350 m, using a portable Oxford Medilog 9000 cassette recorder over 8 consecutive days. The recordings at altitudes of 5000 to 7600 m were performed while attempting to climb Mount Everest without an oxygen mask. The subject slept only at night. Altitude sleep measures were compared to data obtained at 300 m altitude during one 24-h recording performed before the expedition departed. The sleep–wake organization was barely influenced by altitude. Intrasleep wakefulness was augmented, leading to a decrease in sleep efficiency. No slow-wave-sleep curtailment was found, and day-to-day sleep–wake variations were more likely due to anxiety, fatigue owing to strenuous effort, nighttime cold, or daytime heat exposure.