Cognitive performance is associated with cerebral oxygenation and peripheral oxygen saturation, but not plasma catecholamines, during graded normobaric hypoxia

Abstract

New Findings What is the central question of this study?What are the mechanisms responsible for the decline in cognitive performance following exposure to acute normobaric hypoxia? What are the main findings and their importance?We found that (1) performance of a complex central executive task (n‐back) was reduced at FnormalIO2 0.12; (2) there was a strong correlation between performance of the n‐back task and reductions in SnormalpO2 and cerebral oxygenation; and (3) plasma adrenaline, noradrenaline, cortisol and copeptin were not correlated with cognitive performance. Abstract It is well established that hypoxia impairs cognitive function; however, the physiological mechanisms responsible for these effects have received relatively little attention. This study examined the effects of graded reductions in fraction of inspired oxygen (FnormalIO2) on oxygen saturation (SnormalpO2), cerebral oxygenation, cardiorespiratory variables, activity of the sympathoadrenal system (adrenaline, noradrenaline) and hypothalamic–pituitary–adrenal axis (cortisol, copeptin), and cognitive performance. Twelve healthy males [mean (SD), age: 22 (4) years, height: 178 (5) cm, mass: 75 (9) kg, FEV1/FVC ratio: 85 (5)%] completed a four‐task battery of cognitive tests to examine inhibition, selective attention (Eriksen flanker), executive function (n‐back) and simple and choice reaction time (Deary–Liewald). Tests were completed before and following 60 min of exposure to FnormalIO2 0.2093, 0.17, 0.145 and 0.12. Following 60 min of exposure, response accuracy in the n‐back task was significantly reduced in FnormalIO2 0.12 compared to baseline [82 (9) vs. 93 (5)%; P < 0.001] and compared to all other conditions at the same time point [FnormalIO2 0.2093: 92 (3)%; FnormalIO2 0.17: 91 (6)%; FnormalIO2 0.145: 85 (10)%; FnormalIO2 12: 82 (9)%; all P < 0.05]. The performance of the other tasks was maintained. Δaccuracy and Δreaction time of the n‐back task was correlated with both ΔSnormalpO2 [r(9) = 0.66, P < 0.001 and r(9) = −0.36, P = 0.037, respectively] and Δcerebral oxygenation [r(7) = 0.55, P < 0.001 and r(7) = −0.38, P = 0.045, respectively]. Plasma adrenaline, noradrenaline, cortisol and copeptin were not significantly elevated in any condition or correlated with any of the tests of cognitive performance. These findings suggest that reductions in peripheral oxygen saturation and cerebral oxygenation, and not increased activity of the sympathoadrenal system and hypothalamic–pituitary–adrenal axis, as previously speculated, are responsible for a decrease in cognitive performance during normobaric hypoxia.

Is alkalosis the dominant factor in hypoxia‐induced cognitive dysfunction?

“…Surprisingly, there was no effect of the experimental interventions on spatial working memory, which might have been attributable to familiarization during repeated cognitive tests, because the task was not novel. The results contrast with a recent study showing that executive function is impaired after 60 min of poikilocapnic hypoxia in healthy, young, male participants, with evidence of associations between reduced cerebral oxygenation and impaired task accuracy and reaction time (Williams et al., ).…”

Hearables: New Perspectives and Pitfalls of In-Ear Devices for Physiological Monitoring. A Scoping Review

“…SpO 2 is the physiological parameter which tracks the amount of oxygen dissolved in arterial blood or transported oxygen bound to hemoglobin, as indirectly measured at suitable peripheral sites (i.e., finger, toe, forehead, and ear) by pulse oximetry. Since the brain, as well as the muscles, requires a constant oxygen supply to support the high metabolic rate production necessary to remain electrically active (Williams et al, 2019 ), SpO 2 monitoring is of relevance to detect possible risk conditions not only in clinical settings, but also in physiological studies, sport science, and occupational medicine (Costello et al, 2020 ; Pham et al, 2020 ; Stensrud et al, 2020 ). A reduction in oxygen availability, as experienced at high altitudes or in particular challenging situations, can have a detrimental effect on brain and muscles function, inducing performance decline and increasing the risk of errors and injuries (Hoiland et al, 2016 ).…”

A network physiology approach to oxygen saturation variability during normobaric hypoxia

“…This study was part of a larger project investigating effects of normobaric hypoxia on physiological and cognitive function and the experimental design has been described in detail elsewhere (Costello et al., 2020; Williams et al., 2019). A convenience sample of 12 healthy males participated in this study, with mean (SD) age 22 (4) years, height 1.78 (0.05) m, mass 75 (9) kg, FEV1/FVC ratio 85 (5)%.…”

“…This study was part of a larger project investigating effects of normobaric hypoxia on physiological and cognitive function and the experimental design has been described in detail elsewhere (Costello et al, 2020;Williams et al, 2019…”