The effects of acute hypoxia on cognitive and cardiovascular parameters in healthy subjects

Abstract

Background: Hypoxia can affect the health and safety of patients and persons in various occupations. There is uncertainty surrounding the effect acute hypoxia may have on cognition and the cardiovascular system.Aims: The aim was to examine cognition using the Wechsler Abbreviated Scale of Intelligence -First Edition (WASI-I) and investigate heart rate variability (HRV) with varied fraction of inspired oxygen (FiO2) of 0.12, 0.165, and 0.21. Methods: Seventeen healthy volunteers participated in two tasks of the WASI-I: block design (BD) and matrix reasoning (MR). BD, MR, and HRV were measured during randomized gas interventions. A subset had their cerebral tissue oxygenation levels (TOI) evaluated.Results: Cognitive tests for BD (p = 0.133) and MR (p = 0.237) were not significantly different under different O2 concentrations. HRV data showed a decrease in high frequency (HFnu) for MR subset (p = 0.001) with decreasing FiO2. Mean heart rate for BD (p = 0.016) and MR (p = 0.007) increased with decreasing FiO2. NIRS data showed the mean TOI did not significantly change (p = 0.611) during BD; however, during MR, TOI (p = 0.003) decreased with lowering FiO2.Conclusions: Parasympathetic activity and cerebral tissue oxygenation both fell during MR with increasing hypoxia. The cognitive tests did show decreasing trends, albeit non-significant, with increasing severity of hypoxia. HR also increased during hypoxia for both BD and MR. We suspect cognitive function is related to oxygen saturation (SpO2) levels.

The effect of breathing hypoxic gas (15% FIO2) on physiological and behavioral outcomes during simulated driving in healthy subjects

“…This could be a placebo effect. SpO 2 was lower with hypoxic gas, as seen previously (Ravi & Subhan, 2023 ).…”

“…However, our SpO 2 levels (91.7%) were slightly lower to those found in a recent study of COPD patients, where most had a SpO 2 value between 93% and 96% (Echevarria et al, 2021). Our previous work has shown 12% FIO 2 can lower cerebral tissue oxygenation (Ravi & Subhan, 2023), so it is unlikely that our subjects had cerebral hypoxia, although one third of our subjects reported drowsiness, less concentration, lethargy, and headaches. Our subjects had varied driving and gaming experiences; however, all were given a practice and as overall mean differences were compared, individual variations would be negligible.…”

“…Hypoxic gas also resulted in a decrease in SDRR and SD1. Our previous work has also shown an increase HR (Ravi & Subhan, 2023 ), although it did not show a decrease in SDRR and SD1 with hypoxic gas. One reason for this discrepancy could be a lower statistical power in our previous study.…”