Performance during positive pressure breathing after rapid decompression up to 72,000 feet

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, but the ability of aircrew to perform an emergency "get-me-down" maneuver with this system is unknown. 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 feet (18,288 m) or 72,000 feet (21,946 m) in a hypobaric chamber (Experiment 1). Hypoxia was monitored by blood oxygen saturation (SaO2). Experiment 2 assessed the effects of PPB alone on performance. In Experiment 3, performance was measured while the rate of decrease of SaO2 observed in Experiment 1 was replicated with low oxygen mixtures at ground level. During the first 60 s at 72,000 feet, RT increased by 79 ms because of a shift of the whole distribution to the right. PPB at ground level did not increase RT. Decreasing SaO2 at ground level increased RT, but only after a delay. We 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.