Reduction In Oxygen Delivery Under Severe Hypoxia Affects Cognitive Function During Moderate Exercise

Abstract

Reduction in oxygen delivery during hypoxia might impair cognitive function at rest. In contrast, acute moderate exercise can improve cognitive function. A recent study suggested that cognitive function improves during moderate exercise even under moderate hypoxia. However, it is unclear how moderate exercise affects cognitive function under severe hypoxia. PURPOSE:To clarify the effects of moderate exercise on cognitive function under severe hypoxia. METHODS:Thirteen subjects completed cognitive tasks under either normoxia or severe normobaric hypoxia (FIO2; 0.12~0.13) in a randomized crossover design. For each condition, participants underwent preliminary testing to assess peak oxygen uptake (peak VO2) while pedaling an ergometer. After a 5-min warm-up (30% peak VO2), they cycled at moderate intensity (50% peak VO2) for 15 min. Cognitive tasks were performed at rest and 5 min after the start of exercise at moderate intensity. Cognitive tasks were a spatial delayed-response task and a Go/NoGo task, which required working memory and executive function. Pulse oximetric saturation (SpO2) and cerebral oxygenation were monitored throughout the experiment. Cerebral oxygenation was recorded by near infrared spectroscopy and was expressed as changes from baseline. RESULTS:Severe hypoxia significantly decreased SpO2 and cerebral oxygenation at rest relative to normoxia (SpO2: 97.9 ± 0.7 vs. 87.8 ± 1.5 %, p < 0.01; cerebral oxygenation: 0.2 ± 1.3 vs -8.9 ± 1.7 %, p < 0.01). Moreover, relative to rest, exercise significantly decreased SpO2 and cerebral oxygenation under hypoxia (SpO2: 87.8 ± 1.5 vs. 77.5 ± 3.0 %, p < 0.01, cerebral oxygenation: -8.9 ± 1.7 vs. -17.0 ± 2.4 %, p < 0.01). Compared with rest, reaction time (RT) on the Go/NoGo task improved during exercise in both conditions (Normoxia: 1015 ± 315 vs. 862 ± 208 ms, p < 0.01, Hypoxia: 1023 ± 228 vs. 896 ± 236 ms, p < 0.01). Neither exercise nor hypoxia altered the accuracy on the cognitive tasks. In the hypoxic condition, ΔRT was negatively correlated with changes in SpO2 (r = -0.56; p < 0.05). CONCLUSIONS:Acute moderate exercise improves cognitive function even under severe hypoxia. However, the improvements under hypoxia appear to lessen as SpO2 decreases during exercise.