Solute permeability of the alveolar epithelium in acute hemodynamic pulmonary edema in dogs.

Ten anesthetized dogs, 48 h postintravenous 131I-albumin injection, had a segment of lung airspace isolated by a balloon-tipped catheter lodged in a bronchus. An isotonic saline solution containing trace amounts of Blue Dextran, 125I-albumin, and 57Co-cyanocobalamin was instilled into the lung segment. During control periods, lung saline was absorbed at a rate of 0.133% per minute as measured by indicator dilution of Blue Dextran. Only 57Co-cyanocobalamin crossed the epithelium. Acute hemodynamic pulmonary edema was produced by aortic constriction plus saline overload. In pulmonary edema the fluid volume in the airspace increased at the rate of 0.96% per minute, and there was a significant influx of 131I-albumin into the lung saline from the blood in all animals. However, neither 125I-albumin nor Blue Dextran diffused from the airspace into blood during edema; both were merely diluted by fluid influx. The rate of diffusion of 57Co-cyanocobalamin increased fivefold during edema. A small number of discrete breaks in the lung epithelium allowing bulk flow of interstitial fluid is proposed to account for the one-way movement of albumin in hemodynamic alveolar edema.