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 testing 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 SpO2 levels.