• Yvonne Nussbaumer-Ochsner, Justyna Ursprung, Christoph Siebenmann, Marco Maggiorini, and Konrad E Bloch.
• Pulmonary Division and Sleep Disorders Center, University Hospital of Zurich, and Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
• Sleep. 2012 Mar 1;35(3):419-23.

Study ObjectiveObjective 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.DesignProspective observation.SettingOne night in a sleep laboratory at 490 meters, the first and the third night in a mountain hut at 4559 meters.ParticipantsSixteen healthy mountaineers.InterventionAltitude exposure.MeasurementsPolysomnography, questionnaire evaluation of sleep and acute mountain sickness.ResultsCompared 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.ConclusionsIn 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.

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