Effect of high terrestrial altitude and supplemental oxygen on human performance and mood.

Sustained exposure to high terrestrial altitudes is associated with cognitive decrement, mood changes, and acute mountain sickness (AMS). Such impairment in aviators could be a safety hazard. Thirteen male soldiers, ages 19-24, ascended in 10 min from sea level to 4,300 m (simulated), and remained there 2.5 d. Four times per day, subjects completed a test battery consisting of nine cognitive tests, a mood scale, and an AMS questionnaire. During one test session per day, subjects breathed 35% oxygen instead of ambient air. Analysis revealed transient deficits on altitude day 1 for three cognitive tasks. Most tasks displayed a persistent training effect. Sick subjects' moods were more negative and their performance improvement less. On altitude day 1, oxygen administration improved performance on two cognitive tests and one mood subscale. Following rapid ascent to 4,300 m, performance is most affected during the first 8 h. Individuals affected by AMS tend to improve more slowly in performance and have more negative moods than those who feel well.