[Dynamic oxygen tension in the brain of rats under acute hypobaric hypoxia].

In unanesthetized rats at the "altitudes" of 4000 m (1st group) and 8000 m (2nd group), within 1.5 hrs the 1st group developed a 17-30% drop in the PO2 in 43% of cases, no changes occurred in 14% of cases, and in 43% the PO2 increased by 145-205%. In the 2nd group, the PO2 was decreased by 44-87%, on the average. The PO2 changes in the brain cortex under hypoxic conditions seems to have a phasic character as expressed by alternation of increased and decreased levels of the PO2 depending on the degree of hypoxia and induced, apparently, by systemic and local responses compensating for the lack of oxygen in the air.