Pulmonary Vasoconstriction Due to Nonocclusive Distention of Large Pulmonary Arteries in the Dog

Abstract

The pulmonary vascular changes caused by distention of the pulmonary artery with the lumen fixed were compared to those produced by occlusive arterial distention. In 13 urethane-anesthetized dogs, nonocclusive distention was produced by distention of a corrugated rubber cuff around a hollow metal cylinder affixed to the end of a cardiac catheter. In 10 other dogs, occlusive distention was produced by inflation of a standard balloon catheter. Pressures were measured in large and small pulmonary veins and in the left and right atria with transseptal techniques, and in the pulmonary and femoral arteries. Simultaneously, pulmonary blood volume and flow were measured with dyedilution techniques. Pulmonary arteriovenous shunting was studied with the hydrogen-electrode technique. Nonocclusive distention of a pulmonary artery greatly increased pulmonary arterial and venous pressure and decreased pulmonary blood volume without changing left atrial pressure or cardiac output. Pulmonary vascular resistances increased, and pulmonary arteriovenous shunting was detected. Occlusive distention of one pulmonary artery caused smaller increases in pressure in the pulmonary artery and vein of the unobstructed lung. Vascular resistances in the unobstructed lung decreased, while blood volume and flow in that lung doubled. Pulmonary arterial distention leads to active constriction of the pulmonary arteries and veins, but these responses may be obscured by the passive responses to increasing blood flow and volume.