Relationship between Decreased Oxygenation during Acute Hypoxia and Cognitive Deterioration in Healthy Humans

Abstract

BackgroundDespite improvements in military aircraft safety, many aviation incidents are attributed to hypoxia. The correlation between moderate hypoxia and cognitive function are well studied but results remain controversial. Comparatively, the effects of severe hypoxia are still not well understood. In the present study, we examined the executive cognitive function and physiological indices under both moderate and severe hypoxia conditions.PurposeTo examine the relationship between executive function and physiological indices during acute hypoxia exposure.MethodsTen young healthy participants (4M/6F, 29±4 years) completed two different levels of hypoxia: 1) 10 minute moderate hypoxia (MH; FiO2= 0.118) and 2) 3 minute severe hypoxia (SH; FiO2= 0.077) following 3 minute baseline (BL; FiO2=0.209). Reaction time and errors of commission (defined as a response to a non‐target stimulus) were evaluated continuously using a custom Go/No‐go test at baseline and throughout hypoxia exposure. In this Go/No‐go test, participants were required to push a key when upper case “A” or “@” appeared but not when lower case “a” appeared on a computer monitor as quick and as accurately as possible. The stimuli were presented one at a time at any one of nine differing locations across the screen. Cerebral oxygenation (rSO2) was continuously monitored with near‐infrared spectroscopy (NIRS) positioned above the left supraorbital ridge. Finger oxygen saturation (SpO2) was continuously assessed using a pulse oximetry. Data were analyzed in every 30 seconds and are presented as mean±SE. Two‐way ANOVA and Bonferroni test for multiple comparisons was used to evaluate significant differences.ResultsBoth SpO2 and rSO2 were reduced with SH (SpO2 %, BL: 99.3±0.1% vs. SH: 70.7±1.5%, P<0.01; rSO2 %, BL: 70±4% vs. SH: 58±4%, P<0.01). In SH, correlations of SpO2 and rSO2 were significant to the number of errors during the cognitive performance task (SpO2; R= −0.65, rSO2; R= −0.58, Both P<0.01). SH significantly increased errors of commission of the last 30 seconds in 3 minute hypoxic exposure. (BL: 0.6±0.2 errors vs. SH: 1.7±0.5 errors, P<0.01). SH significantly decreased reaction time over hypoxic exposure (BL: 0.43±0.01 sec vs. SH: 0.41±0.01 sec, P<0.01). Comparatively, MH did not elicit an increase in the number of errors of commission nor a decrease in reaction time (Both, P>0.05).ConclusionExecutive function deteriorated during severe hypoxia. Oxygenation of the prefrontal lobe which controls inhibition may be related to the increase in commission errors. Devices that monitor physiological indices such as SpO2 or rSO2 might be beneficial for a model to predict executive deterioration.Support or Funding InformationThis project was funded by the Office of Naval Research (ONR), grant number N00014‐18‐D‐7001‐TO1.