Performance and health effects of mild hypoxic hypoxia in simulated 6-hour exposures between 2,438 and 3,048 metres

Introduction: The Royal Canadian Air Force (RCAF) imposes a daily 4-hour (h)limit for operating unpressurized aircrafts, including helicopters, between 2,438 and 3,048 m (8,000 [8K] and 10,000 [10K] ft) if supplemental oxygen (O2) is unavailable. This regulation may negatively impact RCAF operations because weight and space restrictions limit sufficient O2 to achieve mission success. The effects of exposure durations beyond the 4-h limit are currently unknown, but extensions have the potential to improve operational effectiveness. This study examined the effects of hypoxic exposures on symptoms, mood and performance as a function of altitude and exposure duration. Methods: Seventeen military helicopter pilots were randomly exposed to two 6-h altitude levels (8K and 9.9K) on 2 separate days in a hypobaric chamber. Daily, participants periodically performed a simulated rotary wing flight task, and completed a cognitive test battery. Cerebral regional and finger pulse oxyheamoglobin saturation levels and heart rate were continuously monitored. Participants indicated their subjective hypoxia signs and symptoms, mood and fatigue. Results: Exposure to altitude significantly decreased cerebral and pulse O2 saturations, but values remained steady during the 6-h exposure. No negative decrements were observed on cognition or simulation performance. Self-reported symptoms of fatigue and headache were reported at altitude with a slight increase with time. Discussion: No clear evidence of significant deficits on performance was observed in participants when exposed to mild levels of hypoxia for up to 6 h without supplemental O2.