Fulco, C. S., Demes, R., Muza,S., Beidleman, B., Jones, J., Staab, J., Elliot, L., & Cymerman, A. (June 03, 2010). Sleeping in normobaric hypoxia (760 Torr; 14.4.-16.2% O2) did not cause increased restlessness or AMS. Presentation 1977 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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"Inducing altitude acclimatization during sleep using repeated exposures to normobaric hypoxia (~760 Torr, <20.9% O2) has become a popular adjunct to exercise training. However, if normobaric hypoxia conditions are too severe for unacclimatized individuals, restless sleep (“tossing and turning”) and acute mountain sickness symptoms can occur".

This study determined if sleeping under progressively increasing normobaric hypoxia conditions equivalent to 2,200 to 3,050 m causes increased restlessness or acute mountain sickness. Unacclimatized men and women slept for seven consecutive nights in portable rooms under either normobaric hypoxia (N = 11) or “sham” (N = 6) conditions. The ambient % O2 for the normobaric hypoxia group was progressively reduced by ~0.3% O2 (150 m equivalent) each night from ~16.2% O2 (2,200 m) to ~14.4% O2 (3,050 m) on the seventh night. Ambient O2 for the sham group remained at 20.9%. Both groups were blinded to the treatments. All wore a pulse oximeter that recorded arterial oxygen saturation (SaO2) and heart rate using a finger sensor and a monitor on the wrist to record motion. Recordings occurred for the entire recumbent duration. Sleep duration and number of hourly awakenings were determined by motion quantity. The Environmental Symptoms Questionnaire was administered each morning upon awakening and the cerebral factor score (AMS-C) was calculated.

Each night, SaO2 was lower in the normobaric hypoxia group compared to the sham group. Over the seven nights, SaO2 gradually decreased from 92±2 to 88±3% for the normobaric hypoxia group but remained at 96±1% for the sham group. Heart rate did not differ between groups or within either group over time. Sleep duration (~6.2 hrs) and the % time that each group slept while recumbent (~93%), and rate of awakenings (1-2/hr) did not differ between groups for any night. Moreover, no one in either group developed acute mountain sickness.

Implication. Sleeping under progressive acute mountain sickness conditions equivalent to 2,200-3,050 m does not cause increased restlessness or acute mountain sickness.

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