Influence of Hypoxia on the Pulmonary Circulation of Nonnarcotized Dogs

Abstract

Methods are descr. for measuring intracardiac pressures and cardiac output in the normal, trained nonnarcotized dog breathing 8% O2 in N (hypoxia). Under such exptl. conditions, the following respiratory and circulatory changes were observed. 1) An increase in pulmonary artery pressure amting. to 4-5 mm. Hg and beginning with 1 min. after onset of hypoxia. This increase reached a plateau after 5 min. and maintained itself during the entire period of hypoxia. Pulmonary artery pressure fell to its control level within 1-2 min. after cessation of the low O2 mixture. 2) No significant change in left atrial pressure. 3) A 34% increase in heart rate. 4) An increase in cardiac output measured 5 min. after hypoxia. This increase amounted to 56% when calculated by the dye dilution method and 35% the pulse contour method. 5) The increased cardiac output could account for the increased pulmonary artery pressure without postulating an increased pulmonary vascular resistance. 6) A significant fall in O2 uptake measured 5 min. after onset of hypoxia, over a 5-min. period.