Abstract
It is generally well accepted that acute exposure to a hypoxic environment may impair both physical and cognitive performance. Whilst the effects on physical performance are well established, comparatively the effects on cognitive performance are poorly understood. Accordingly, the studies presented in this thesis examined the physiological response to an acute bout of normobaric hypoxia and the impact on cognitive performance at rest, during exercise, and when acute hypoxia and one night of total sleep deprivation were combined. This thesis comprises a systematic review and meta-analysis, two empirical investigations, and a retrospective reliability analysis.The first study within this thesis is a systematic review and meta-analysis that examined cognitive performance during acute exposure (< 6 hours in duration) to altitudes ranging from 2400 to 5800 m (or a simulated equivalent) in unacclimated individuals at rest. In total 23 studies consisting of 364 particpants were included for analysis. The findings provide some evidence for hypoxia induced cognitive impairment across multiple domains. However, due to the high level of study bias, these findings should be treated with caution.
Using a randomised controlled cross-over design, this published experimental study (n = 12) used graded reductions in the fraction of inspired oxygen (FIO2) (0.2093, 0.17, 0.145, 0.12) to map the physiological and cognitive responses to increasing levels of hypoxia at rest. The results of this investigation demonstrated that performance of the 3-back task (working memory) was reduced at an FIO2 of 0.12. Performance of the 3-back task was correlated with both Δ peripheral oxygen saturation (SpO2) and Δ oxygenation of the prefrontal cortex (PFC), however, there was no relationship between cognitive performance and plasma catecholamines.
The next experimental study (n = 12) extended the work from the second investigation and explored the isolated and combined effects of hypoxia (FIO2 0.12), moderate intensity exercise, and one night of total sleep deprivation on cognitive performance. In contrast to the previous investigation (study 2), cognitive performance was maintained in hypoxia, potentially related to higher SpO2 values, however one night of total sleep deprivation resulted in a reduction in performance across each of the cognitive tasks. When hypoxia and sleep deprivation were experienced in combination, no further decrements in performance were observed. When compared to resting performance in the same conditions, moderate intensity exercise improved cognitive performance in both normoxia and hypoxia after one night of total sleep deprivation.
The final study was a retrospective analysis that examine the with and between day reliability of the software used for the assessment of cognitive performance. The changes observed due to experimental manipulations (hypoxia, exercise, sleep deprivation) were greater than the within and between day coefficient of variation.
In summary, the findings reported in this thesis demonstrate that there is considerable interindividual variation in the response to acute hypoxia and therefore the performance of cognitive tasks. Whilst the results of these studies provide some evidence that cognitive performance may be related to the extent of the reduction in arterial oxygen content and desaturation of the PFC, the exact physiological mechanism(s) that govern cognitive performance in hypoxia are still to be elucidated. The finding that moderate intensity exercise may improve sleep deprivation-induced decrements in cognitive performance in both normoxia and hypoxia, provides an exciting avenue for further exploration.
| Date of Award | 17 May 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Joe Costello (Supervisor), Jo Corbett (Supervisor) & Mike Tipton (Supervisor) |