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, 35 (3), 419-23

Effect of Short-Term Acclimatization to High Altitude on Sleep and Nocturnal Breathing

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Effect of Short-Term Acclimatization to High Altitude on Sleep and Nocturnal Breathing

Yvonne Nussbaumer-Ochsner et al. Sleep.

Abstract

Study objective: Objective physiologic data on sleep and nocturnal breathing at initial exposure and during acclimatization to high altitude are scant. We tested the hypothesis that acute exposure to high altitude induces quantitative and qualitative changes in sleep and that these changes are partially reversed with acclimatization.

Design: Prospective observation.

Setting: One night in a sleep laboratory at 490 meters, the first and the third night in a mountain hut at 4559 meters.

Participants: Sixteen healthy mountaineers.

Intervention: Altitude exposure.

Measurements: Polysomnography, questionnaire evaluation of sleep and acute mountain sickness.

Results: Compared to 490 m, median nocturnal oxygen saturation decreased during the 1st night at 4559 m from 96% to 67%, minute ventilation increased from 4.4 to 6.3 L/min, and the apnea-hypopnea index increased from 0.1 to 60.9/h; correspondingly, sleep efficiency decreased from 93% to 69%, and slow wave sleep from 18% to 6% (P < 0.05, all instances). During the 3rd night at 4559 m, oxygen saturation was 71%, slow wave sleep 11% (P < 0.05 vs. 1st night, both instances) and the apnea/hypopnea index was 86.5/h (P = NS vs. 1st night). Symptoms of AMS and of disturbed sleep were significantly reduced in the morning after the 3rd vs. the 1st night at 4559 m.

Conclusions: In healthy mountaineers ascending rapidly to high altitude, sleep quality is initially impaired but improves with acclimatization in association with improved oxygen saturation, while periodic breathing persists. Therefore, high altitude sleep disturbances seem to be related predominantly to hypoxemia rather than to periodic breathing.

Keywords: Altitude; apnea; hypoxia; sleep; ventilation.

Figures

Figure 1
Figure 1
The hypnogram obtained in a subject during a night at 490 m (top panel) shows a normal distribution of sleep stages and several NREM/REM sleep cycles. In contrast, the hypnogram recorded during the 1st night at 4559 m (middle panel) reveals predominantly superficial sleep stages with frequent awakenings, very rare deep sleep stages 3 and 4, and no REM sleep. The hypnogram from the 3rd night at 4559 m (bottom panel) reveals a partial restoration of normal sleep architecture.
Figure 2
Figure 2
Medians and quartile ranges (bars, vertical lines) of the apnea/hypopnea index (AHI) and the apnea/hypopnea related arousal index at 490 m and the 1st and the 3rd night at 4559 m. Only 11% and 4% of the apneas/hypopneas were followed by an arousal during the 1st and the 3rd nights, respectively. *P < 0.05 vs. 490 m, #P < 0.05 vs. the 1st night at 4559 m.

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