Positive pressure breathing (PPB) is a survival system that delivers high-pressure oxygen and body counterpressure in the event of cockpit depressurization at high altitude. The ability of aircrew to perform an emergency "get-me-down" maneuver with this system is questionable. To address this question, a serial choice reaction time (RT) task was administered to six participants, who were sustained with PPB after rapid decompression to 60,000 ft (18,288 m) or 72,000 (21,946 m) in a hypobaric chamber (Experiment 1). Hypoxia was monitored by blood oxygen saturation. Experiment 2 assessed the effects of PPB alone on performance. In Experiment 3, performance was measured while the rate of decrease of blood oxygen saturation observed in Experiment 1 was reproduced with low oxygen mixtures at ground level. During the first 60 s at 72,000 ft, RT rose by 79 ms because of a shift of the whole distribution to the right. PPB at ground level did not increase RT. Decreasing blood oxygen saturation at ground level increased RT, but only after a delay. The authors conclude that inattention to the task, PPB alone, or surprisingly, hypoxia cannot explain the majority of the impairment observed in Experiment 1. Rather, PPB and low pressure at high altitude interacted to exacerbate lacrimation, thereby degrading vision. Implications for the design of get-me-down maneuvers are discussed.
Abstract