Mild hypoxia, mood and complex cognition in pilots

Thirty six volunteer airforce personnel were sequentially exposed in a randomized balanced order in a hypobaric chamber in three runs each comprising approximately 30 minutes of exposure to each of baseline (sea level), a specified altitude (equivalent to sea level, 8000ft and 12,000ft), and followed immediately by breathing 100% oxygen from an oro-nasal mask. In each run for each exposure, mood and complex cognition were assessed (after 4 prior practices) using tests for profile of mood states (vigor, anxiety, depression, fatigue, happiness, restlessness, anger) and complex cognition (memory search, processing speed (Stroop test), mathematical processing, 3-dimensional spatial rotation (Manikin test), logical relations, decision-making/mental flexibility (Tower puzzle test)). Analysis of variance indicated that feelings of fatigue and vigor remained the same at 8000ft but fatigue was increased (p = 0.001) and vigor reduced (p =0.035) at 12,000ft and was restored by supplementary oxygen. For logical relations, there was an unexpectedly high value (37.1) during the ‘altitude’ exposure at sea level suggestive of an improvement due to practice from baseline. At 8000ft and 12,000ft there was no difference from baseline, suggesting that any improvements in performance may have been negated by hypoxia. With supplementary oxygen, performance may also have fallen, perhaps because of the effect of the mask and/or time-related fatigue. Although the value of 37.1 for the sea level ‘altitude’ condition was unexpected, the findings are consistent with a decrement in logical relations in mild hypoxia. Overall however, the analysis failed to support the view that mood and complex cognition is materially impaired by mild hypoxia but that some aspects of mood (fatigue and vigor) and complex cognition (logical relations) may have been influenced. Practitioner Summary: Aircrew may feel more fatigued and less vigorous at a cabin altitude of 12,000ft. This can be restored by supplementary oxygen. There was indirect evidence that performance for logical relations may be impaired at 12,000ft.