Acute hypoxic gas breathing severely impairs cognition and task learning in humans

Impairments in neural function are common when oxygen supply to the brain is reduced. This study examined neurocognitive processes that are vulnerable to oxygen deprivation. We induced moderate-to-severe hypoxia in healthy adults, thereby inducing impairments caused by low brain oxygen availability. 22 healthy adults participated in this matched-pairs study with a single-blind, randomised design. Baseline neurocognitive function was examined during a familiarisation trial and participants were assigned to hypoxia (10% O2) or sham (21% O2) groups. Neurocognitive performance was assessed via computerised test battery after 50 min of breathing a gas mixture that reduced arterial oxygen saturation by 20% (p<0.01). Hypoxia severely reduced performance across all neurocognitive domain scores; with significant drops in neurocognitive index (-20%), composite memory (-30%), verbal memory (-34%), visual memory (-23%), processing speed (-36%), executive function (-20%), psychomotor speed (-24%), reaction time (-10%), complex attention (-19%) and cognitive flexibility (-18%; all p<0.05). Practice effects were blocked by hypoxia but occurred in sham for information processing speed (+30%), executive function (+14%), psychomotor speed (+18%), reaction time (+5%), cognitive flexibility (+14%), and overall cognitive functioning (+9%; all p<0.05). Neuropsychological performance decrements caused by acute experimental hypoxia are comparable to cognitive domains impaired with high altitude exposure and mild traumatic brain injury.