Effect of edema on pulmonary blood flow in the isolated perfused dog lung lobe

We determined the relationship between the amount of edema and changes in blood flow in the isolated, perfused, and ventilated lower lobe of dog lung. We held vascular pressure constant and measured lobe weight and flow continuously. Vascular pressures were set to produce minimal weight gain in four lobes (controls) and large weight gain in six lobes (edema). In all lobes, the outflow pressure exceeded alveolar pressure at end expiration (zone III conditions). The control lobes gained an average of 20% in weight over 4 h, but blood flow remained constant. They showed interstitial edema histologically and extravascular lung water was increased 38%. The edema lobes gained weight rapidly, ultimately tripling their weight. In these lobes, blood flow remained constant until lobe weight had doubled; then flow decreased progressively to low levels. These lobes showed extensive alveolar edema histologically and extravascular lung water was increased 238%. Pulmonary blood flow is not affected by interstitial edema, but is markedly reduced when alveolar flooding occurs.