Impact of rapid ascent to high altitude on sleep.

Objective: Sleep disturbance at high altitude is common in climbers. In this study, we intended to evaluate the effect of rapid ascent on sleep architecture using polysomnography (PSG) and to compare the differences between subjects with and without acute mountain sickness (AMS).

Methods: The study included 40 non-acclimatized healthy subjects completing PSG at four time points, 3 days before the ascent (T0), two successive nights at 3150 m (T1 and T2), and 2 days after the descent (T3). All subjects were transported by bus from 555 to 3150 m within 3 h. AMS was diagnosed using self-reported questionnaire of Lake Louise score.

Results: Twenty of 40 (50%) subjects developed AMS. At high altitude, awakening percentages increased in AMS group but changed insignificantly in non-AMS group. Arousal index and apnea/hypopnea index (AHI) increased irrespective of AMS. The increases of AHI were more evident in non-AMS group than in AMS group. Compared to subjects without AMS, those with AMS had significantly lower sleep efficiency, lower central apnea index, and longer latencies to sleep and rapid eye movement (REM) sleep at T1 and lower REM sleep percentages at T1 and T2. Subjects with older age and lower minimum arterial oxygen saturation during sleep at sea level were prone to develop AMS.

Conclusions: Higher AHI did not cause more frequent awakenings and arousals at high altitude. Central sleep apneas were observed in non-AMS but not in AMS group. Subjects unacclimatized to acute hypobaric hypoxia might have delayed and less REM sleep.