Cerebral oxygenation and cognitive performance under different acute normobaric hypoxic conditions: a fNIRS study

This study investigates the effects of different levels of acute normobaric hypoxia on cognitive function and cerebral oxygenation in healthy young adults.

Twenty-four participants aged 18-30 years were exposed to hypoxia with an inspired oxygen fraction (FiO₂) equivalent to 20.9%, 17.44%, 14.5% and 12.7%. They performed different cognitive tasks, including the Stroop test, Corsi blocks (forward and backward), the n-Back task (1-Back and 2-Back), and the Go/No-Go task. Cerebral oxygenation was measured using the near-infrared spectroscopy (NIRS) during each cognitive task.

In this study, we did not observe any effect of hypoxia on cognitive performance. However, perceived difficulty increased with increasing hypoxia, especially for the Stroop task (p = 0.003, Kendall's W = 0.208) and Corsi (p = 0.018, Kendall's W = 0.152). NIRS results showed a progressive increase in deoxyhemoglobin (ΔHHb) and a progressive decrease in oxyhemoglobin (ΔO₂Hb) with increasing hypoxia for all cognitive tasks. There was no effect on total hemoglobin (ΔtHb). Finally, positive correlations were found between pulse oxygen saturation (SpO₂) and ΔTSI% and between SpO₂ and ΔO₂Hb for all tasks, while a negative correlation was observed between SpO₂ and ΔHHb. No correlation was found between SpO₂ or TSI% and cognitive performance.

In conclusion, cognitive function appears to be unaffected by acute exposure to acute normobaric hypoxia at FiO₂ above 12.7%. These results suggest a complete compensation of oxygenation of the prefrontal cortex region in young healthy subjects.