Acute hypoxia impairs posterior cerebral bioenergetics and memory in man

Hypoxia has the potential to impair cognitive function, however, it is still controversial which cognitive domains are adversely affected. The present study examined the effects of acute hypoxia (~7 hours) on central executive (Go/No-Go) and non-executive (memory) tasks, and to what extent impairment was potentially related to regional cerebral blood flow (CBF) and oxygen delivery (CDO2). Twelve male participants performed cognitive tasks following 0 h, 2 h, 4 h, and 6 h passive exposure to both normoxia and hypoxia (12% O2), in a randomized block cross-over single-blinded design. Middle cerebral artery (MCA) and posterior cerebral artery (PCA) blood velocities and corresponding CDO2 were determined using bi-lateral transcranial Doppler ultrasound. In hypoxia, MCA DO2 was reduced during the Go/No-Go task (p = 0.010, vs. normoxia, main effect), and PCA DO2 attenuated during memorisation (p = 0.005, vs. normoxia) and recall components (p = 0.002, vs. normoxia) in the memory task. The accuracy of the memory task was also impaired in hypoxia (p = 0.049, vs. normoxia). In contrast, hypoxia failed to alter reaction time (p = 0.19, vs. normoxia) or accuracy (p = 0.20, vs. normoxia) during the Go/No-Go task, indicating that selective attention and response inhibition were preserved. Hypoxia did not affect CBF or corresponding CDO2 responses to cognitive activity (p > 0.05, vs. normoxia). Collectively, these findings highlight the differential sensitivity of cognitive domains with memory selectively vulnerable in hypoxia.