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

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

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