Sleeping In Normobaric Hypoxia (760 Torr; 14.4-16.2% O2) Did Not Cause Increased Restlessness Or AMS

Abstract

Inducing altitude acclimatization during sleep using repeated exposures to normobaric hypoxia (NH; ∼760 Torr, <20.9% O2) has become a popular adjunct to exercise training. However, if NH conditions are too severe for unacclimatized individuals, restless sleep ("tossing and turning") and acute mountain sickness (AMS) symptoms can occur. PURPOSE: To determine if sleeping under progressively increasing NH conditions equivalent to 2200 to 3050 m causes increased restlessness or AMS. METHODS: 17 healthy, unacclimatized men and women slept for 7 consecutive nights in portable rooms (Colorado Altitude Training, Louisville, CO) under either NH (n=11, 25±6 yr, 77±16 kg; mean±SD) or "sham" (n=6, 25±5 yr, 73±19 kg) conditions. The ambient % O2 for the NH group was progressively reduced by ∼0.3% O2 (150 m equivalent) each night from ∼16.2% O2 (2200 m) on the 1st night to ∼14.4% O2 (3050 m) on the 7th night, while ambient O2 for the sham group remained at 20.9%. Both groups were blinded to the treatments. All wore a pulse oximeter (Nonin, Plymouth, MN) that recorded arterial oxygen saturation (SaO2) and heart rate (HR) using a finger sensor and a monitor on their wrist (Ambulatory Monitoring Inc, Ardeley, NY) 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. RESULTS: Each night, SaO2 was lower (P<0.001) in the NH group compared to the sham group. Over the 7 nights, SaO2 gradually decreased (P<0.05) from 92±2 to 88±3% for the NH group but remained at 96±1% for the sham group. HR did not differ between groups or within either group over time (∼64 b/min). 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 AMS. CONCLUSION: Sleeping under progressive NH conditions equivalent to 2200-3050 m does not cause increased restlessness or AMS. Funding provided by US Army Medical Research Materiel Command ATO IV.MD.2006.01. Authors' views; not official U.S. Army or DoD policy.