Electrical activity of the brain and oxygen supply for cognitive-mnestic activity in humans under different degrees of hypoxia

Abstract

Comparative analysis of the indices of oxygen supply for the body and the brain and the functional state of the brain was carried out in three experimental situations: performance of cognitive-mnestic tests under normoxic (TN) and hypoxic conditions (TH) and exposure to hypoxia in the absence of cognitive tasks (H). Each subject participated in all of the experiments. Hypoxic conditions were created by breathing of a hypoxic gas mixture (HGM) consisting of oxygen and nitrogen for 25 min. The first group (eight subjects) was exposed to moderate hypoxia, with the gas mixture containing 12% O2 (HGM-12); the second group (eight subjects) was exposed to severe hypoxia, with the gas mixture containing 8% O2 (HGM-8). The cognitive-mnestic activity (CMA) under both normoxia and hypoxia was continuous and included the following tests: “Arithmetic calculations,” “Memory for numerals,” “Colored figures”, and “Sensorimotor response time.” The CMA efficiency was significantly impaired only under severe hypoxia (HGM-8). The CMA efficiency was higher in some subjects of the first group (HGM-12) in the TH series as compared to that in the TN series. The EEG spectral power (SP) during CMA was decreased as compared to the background in all subjects in the TN series and in most subjects of the first group, exposed to HGM-12, whereas it was increased in all subjects of the second group, exposed to HGM-8. The EEG SP was lower in most subjects of both groups studied in the TH series as compared to that found in the H series. The rheographic index of cerebral blood flow rate was not changed compared to the background in the TN series and was increased in the H and TH series during HGM-8 treatment. The increase in cerebral blood flow was less pronounced in the TH series as compared to the H series in most subjects of the second group (HGM-8). Oxygen consumption by the body was elevated by 10–20% in the TN series. A significant increase in oxygen consumption was found in the subjects of both groups studied during hypoxia treatment (H), and it was greater in HGM-12. The following differences were found between the subjects of the two experimental groups: the increase in oxygen consumption in most subjects of the first group (HGM-12) was higher in the TH series as compared to the H series, whereas, in most subjects of the second group (HGM-8), the increase in oxygen consumption was higher in the H series. The data are discussed from the point of view of synergic and concurrent relationships between different forms of energy expenditure on structural and functional reorganization and organ-specific functions.