Effects of Unilateral Hypoxia and Hypercapnia on Pulmonary Blood Flow Distribution in the Dog

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Abstract
Effects of hypoxia and of hypercapnia on pulmonary blood flow distribution were examined in 19 dogs. The blood flow through each lung was continuously recorded; the test gas was administered to one lung, and the other lung was used as the control. Low oxygen gas mixtures were administered to one lung for periods of 2–47 minutes. When constriction occurred, it began within one-half minute after the gas administration was started and reached a plateau within 8–20 minutes. Vasodilation was never observed. In most animals no vasomotor effect of hypoxia was found early in the experiment (less than 6 hr. after induction of anesthesia), but seven of the early nonreactors became positive later in the experiment. After 6–8 hours from induction of anesthesia, all animals tested showed a vasoconstrictor response to hypoxia. The administration to one lung of 5 or 10% carbon dioxide for 2–10 minutes was always accompanied by vasoconstriction in that lung. In dogs that showed unilateral pulmonary vasoconstriction during hypoxia, further vasoconstriction was produced by adding 5% carbon dioxide. Some of the contradictory results of other investigators may be explained by the refractory period observed in these experiments.

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