Effect of Chronic Hypoxia on the Pulmonary Circulation of Cats. ∗

Abstract

Summary

Cats subjected to chronic exposure to an oxygen-deficient environment (10%) at an early age thrive and develop an increased systolic pressure in the right ventricle (average 69 mm Hg compared to 32 mm Hg in littermates subjected to acute exposure). The pressure decreases when the cats breathe normal air (average pressure, 59 mm compared to 17 in littermates) but does not decrease to normal when 99.6% oxygen is breathed (average pressure, 55 mm compared to 15 in littermates). The average hematocrit value was 52 compared to 26% in controls. The increase in pressure is not a consequence of the increased hematocrit value, change in cardiac output, or delay in closure of the ductus arteriosus. Evidence is presented that the same systolic pressure exists in the pulmonary artery as in the right ventricle and that the most likely cause of the increased ventricular pressure is an increased resistance to blood flow through the pulmonary vessels. There was no evidence of anatomic changes in the pulmonary vessels.