Effect of Mild Hypoxia on Working Memory, Complex Logical Reasoning, and Risk Judgment

Abstract

Mild hypoxia, typically equivalent to a pressurized aircraft cabin altitude of 2,438 m (8,000 ft), does not generally affect well-learned cognitive, vigilance, and perceptual-motor performance. Learning and novel and complex cognitive tasks involving multiple demands, however, might be impaired. This study evaluated whether complex cognition—as assessed by complex reasoning, multiple memory, and risk judgment—was impaired during mild hypoxia. Using a normobaric single-blind crossover design, 25 healthy nonsmoking male participants breathed normoxic (F_iO₂ = 0.206) or hypoxic air (F_iO₂ = 0.143) equivalent to 2,438 m for 2 hr and performed the following tasks at baseline, 30 min, and 90 min: (a) a complex logical reasoning task that assessed accuracy, response time, and a reasoning quality index for easy (nonconflict valid), difficult (nonconflict invalid), fairly difficult (conflict valid), and very difficult (conflict invalid) syllogisms; (b) a multiple memory test that assessed sentence judgment error, working memory span, and prospective memory; and (c) a simple vigilance psychomotor task that assessed the frequency and mean time that a disc was outside a target area and braking reaction time. They also completed a self-perceived risk judgement questionnaire near the end of each exposure. After 90 min, the mean change in working memory span for mild hypoxia (M = 0.9, SD = 4.6) was significantly less than for normoxia (M = 4.4, SD = 7.2). The reasoning quality index for conflict invalid syllogisms for mild hypoxia (M = 0.22, SD = 0.29) was marginally significantly less than for normoxia (M = 0.39, SD = 0.35). The chances of these findings occurring by chance cannot be discounted, but are small. Although this study suggests that mild hypoxia might impair working memory and complex logical reasoning involving difficult conflicts, further studies using more discerning tests of cognition are warranted.

ACKNOWLEDGMENTS

Bryan Dobson from DTA and Flight Lieutenant Gareth Iremonger from AMU provided valuable professional input to the study design. Associate Professor Hugh Morton was consulted in the preparation of this article; he is a Fellow of the Institute of Statisticians, a trained biostatistician and biomathematician, and an Editor and Statistical Consultant for the European Journal of Applied Physiology.