Relative Severity of Human Performance Decrements Recorded in Rapid vs. Gradual Decompression.

Cabin decompression presents a threat in high-altitude-capable aircraft. A chamber study was performed to compare effects of rapid (RD) vs. gradual decompression and gauge impairment at altitude with and without hypoxia, as well as to assess recovery. There were 12 participants who completed RD (1 s) and Gradual (3 min 12 s) ascents from 2743-7620 m (9000-25000 ft) altitude pressures while breathing air or 100% O₂. Physiological indices included oxygen saturation (So₂), heart rate (HR), respiration, end tidal O₂ and CO₂ partial pressures, and electroencephalography (EEG). Cognition was evaluated using SYNWIN, which combines memory, arithmetic, visual, and auditory tasks. The study incorporated ascent rate (RD, gradual), breathing gas (air, 100% O₂) and epoch (ground-level, pre-breathe, ascent-altitude, recovery) as factors. Physiological effects in hypoxic "air" ascents included decreased So₂ and end tidal O₂ and CO₂ partial pressures (hypocapnia), with elevated HR and minute ventilation (V˙); So₂ and HR effects were greater after RD (-7.3% lower and +10.0 bpm higher, respectively). HR and V˙ decreased during recovery. SYNWIN performance declined during ascent in air, with key metrics, including composite score, falling further (-75% vs. -50%) after RD. Broad cognitive impairment was not recorded on 100% O₂, nor in recovery. EEG signals showed increased slow-wave activity during hypoxia. In hypoxic exposures, RD impaired performance more than gradual ascent. Hypobaria did not comprehensively impair performance without hypoxia. Lingering impairment was not observed during recovery, but HR and V˙ metrics suggested compensatory slowing following altitude stress. Participants' cognitive strategy shifted as hypoxia progressed, with efficiency giving way to "satisficing," redistributing effort to easier tasks.