Prostacyclin (not nitroprusside) preserves venous admixture in the injured canine lung.

Abstract

To compare the effects of a prostaglandin vasodilator (prostaglandin I2 [PGI2]) with that of sodium nitroprusside in the isolated lung during 3% and 35% oxygen ventilation. Pulmonary vascular resistance was divided into arterial, middle, and venous segmental resistances. Left lower lobes were injured in a patchy (atelectasis) or diffuse (oleic acid-induced edema) manner. Nitroprusside diminished, but PGI2 ablated, the usual increase in middle segment resistance observed during 3% oxygen ventilation in atelectatic lobes. In the oleic acid-treated lobes, both nitroprusside and PGI2 ablated the increase in middle segment resistance during 3% oxygen ventilation. During nitroprusside administration, as pulmonary vascular resistance decreased, venous admixture proportionately increased, but this correlation was lost during PGI2 administration. We hypothesize that exogenous PGI2 dilates the vessels most constricted by hypoxia but to a lesser degree than does nitroprusside. Therefore, increases in venous admixture may be reduced during PGI2 administration, compared with nitroprusside administration.