Interaction of Chronic Hypoxia and Hypercapnia upon Blood Gases and Acid Base Status 1

Abstract

Summary

Young adult male Charles River rats were exposed for 4 days, in groups of 10 each, to an inspired P _CO2 of 0, 30, 60 and 90 Torr, combined with an inspired P _O2 of 70 or 140 Torr. Arterial P _O2 in the rats inspiring a P _O2 of 70 Torr increased from a mean of 37 Torr, with no added CO₂, to 59 Torr with a PI_o2 of 90 Torr. In the rats breathing normal oxygen levels (140 Torr), arterial blood P _O2 increased from 72 Torr, with no added CO₂, to 101 Torr with a PI_co2 of 90 Torr. Standard bicarbonate increased with increasing PI_co2 in all groups; however, it was consistently lower in the low-oxygen-breathing rats than in the normoxic animals (p < .05). On the other hand, arterial P _CO2 was significantly lower in the hypoxic rats, owing to hypoxic hyperventilation, only when inspired CO₂ levels were 0. This resulted in a lower arterial blood pH in the hypoxic than in the nonhypoxic rats inspiring comparable CO₂ levels (p < .01).