Author(s): FAUCHER, C., MATHE, N., SAULNIER, P.J., MAQUA, A., THEUROT, D., BOULARES, A., GIMENES, M., DUGUE, B., PICHON, A., DUPUY, O., Institution: UNIVERSITY OF POITIERS, Country: FRANCE, Abstract-ID: 2063

INTRODUCTION:
The association between cerebral oxygen level and cognitive function is extensively documented in the normal oxygen range. However, the heterogeneity in protocols designed to investigate the impact of hypoxia-induced changes in cognitive function prevents definitive conclusions regarding underlying mechanisms of cognitive performance. In this study, we aimed to assess the effect of acute normobaric hypoxic conditions on cognitive functions and cerebral oxygenation.
METHODS:
We enrolled healthy participants aged 18 to 30 in a crossover study to explore the effects of 4 simulated altitudes on executive function. These altitudes included normoxia at sea level (SL; FiO2: 21%), low hypoxia (1600 m altitude; FiO2:17.2%), moderate hypoxia (3000 m altitude; FiO2:14.4%), and high hypoxia (4100 m altitude; FiO2:12.5%). Executive function was assessed using 4 standardized cognitive tasks: Stroop task, N-Back, Corsi blocks, and Go/No-Go. The sequence of cognitive tasks and altitude conditions were randomized. Peripheral oxygen saturation (SpO2) and heart rate (HR) were continuously monitored. Cerebral oxygenation was measured using near-infrared spectroscopy during each condition. Changes in the tissue saturation index (ΔTSI%), total hemoglobin (ΔtHb), deoxyhemoglobin (ΔHHb), and oxyhemoglobin (ΔO2Hb) were defined as the difference between each hypoxia level and the normoxia resting state. Perceived exertion after each task was assessed using the DP15 rating scale.
RESULTS:
In 23 participants (22.2±2.8 years; 11 females and 12 males), SpO2 decreased with increasing hypoxia dose, and each condition was different from the others (p<0.001). There was a significant association between perceived exertion level after the Stroop task and hypoxic level (p=0.003) but not after the other 3 cognitive tasks (p=0.098 to 0.977). The hypoxia was only statistically associated with accuracy during the Stroop task (the higher the hypoxia, the higher the mean error rate during the task; p=0.039) but not with other tasks. No significant change in tissue saturation and total hemoglobin (ΔTSI% and (ΔtHb) were found. However, there was a statistically significant increase in deoxyhemoglobin values (ΔHHb) and a significant decrease in oxyhemoglobin (ΔO2Hb) for every cognitive task with the severity of hypoxia.
CONCLUSION:
In summary, our findings suggest that only severe acute normobaric hypoxia impacts executive functions in young healthy subjects. This modest effect may be partially due to compensatory mechanisms operating at the cerebral oxygen extraction level. Nevertheless, participants reported a progressively increased in the perception of task difficulty under all progressive hypoxia levels during every demanding task suggesting a larger cognitive cost.