Acclimation to Hypoxia Does Not Improve Hypoxic Survival of the Immature Pig in Confined Atmosphere

Abstract

Humans may be accidentally trapped in a confined atmosphere in which oxygen availability is limited. If acclimation would extend survival, hypoxic acclimation in confined spaces would be recommended. After hypoxic acclimation, an immature pig was transferred into an experimental sealed chamber. The O2, CO2, chamber temperature, and pressure changes due to the animal's breathing were recorded. Six days acclimation (n = 3) and 3 weeks of acclimation (n = 3) were compared to control pigs (n = 3). No signs of acute mountain sickness were noted in the pigs acclimated for 6 days, but some acute symptoms (which were resolved on the following day) were observed during the 3-week acclimation. The terminal partial pressure of inspired oxygen (PIO2; 3.5-3.6 kPa) was not affected by hypoxic acclimation. Oxygen consumption and CO2 production were similar in the three experimental groups. Our hypothesis that hypoxia acclimation would produce improved survival in a confined space was not supported by the results. It is possible that at very low inspired oxygen of 3.6 kPa, the oxygen consumption of critical life-supporting tissue reached the limit of viable cells in mammals. If this is right, no further improvement could be expected after hypoxic acclimation.