Neurovascular and cortical responses to hyperoxia: enhanced cognition and electroencephalographic activity despite reduced perfusion.

Extreme aviators continually inspire hyperoxic gas to mitigate risk of hypoxia and decompression injury. This neuroprotection carries a physiological cost: reduced cerebral perfusion (CBF). As reduced CBF may increase vulnerability to ever-present physiological challenges during extreme aviation, we defined the magnitude and duration of hyperoxia-induced changes in CBF, cortical electrical activity and cognition in 30 healthy males and females. Magnetic resonance imaging with pulsed arterial spin labelling provided serial measurements of global CBF (gCBF), first during exposure to 21% inspired oxygen ( F I , O 2 ) followed by a 30-min exposure to 100% F I , O 2 . High-density EEG facilitated characterization of cortical activity during assessment of cognitive performance, also measured during exposure to 21% and 100% F I , O 2 . Acid-base physiology was measured with arterial blood gases. We found that exposure to 100% F I , O 2 reduced gCBF to 63% of baseline values across all participants. Cognitive performance testing at 21% F I , O 2 was accompanied by increased theta and beta power with decreased alpha power across multiple cortical areas. During cognitive testing at 100% F I , O 2 , alpha activity was less desynchronized within the temporal regions than at 21% F I , O 2 . The collective hyperoxia-induced changes in gCBF, cognitive performance and EEG were similar across observed partial pressures of arterial oxygen ( P a O 2 ), which ranged between 276-548 mmHg, and partial pressures of arterial carbon dioxide ( P aC O 2 ), which ranged between 34-50 mmHg. Sex did not influence gCBF response to 100% F I , O 2 . Our findings suggest hyperoxia-induced reductions in gCBF evoke enhanced levels of cortical arousal and cognitive processing, similar to those occurring during a perceived threat.