Pulmonary Surface Activity in Induced Pulmonary Edema*

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Abstract
The effect of pulmonary edema on surface activity of lung extracts was examined in 24 anesthetized dogs. Pulmonary edema was induced by intravenous infusion of dextran, and surface tension properties were measured on saline extracts of lungs. Pressure-volume relations were determined in excised lobes and compared with normal controls. Dark, "atelectatic" portions of edematous lungs, scattered throughout, but most marked in dependent parts, showed significantly increased maximal and minimal surface tension (p< 0.001), and significantly decreased extract stability index (p <0.001). When edema was induced in degassed, non-ventilated lung and no foaming occurred, surface properties were ab-normal, but less so than in lung permitted to foam (p<0.05). Edematous lung lobes with considerable morphologic alteration showed a signifi-cantly reduced "expansion index" relative to normal lobes (p 0.001). We conclude that pulmonary edema leads to a regional impairment of pulmonary surface activity, associated with premature alveolar closure. The mechanism of altered surface activity was not explained fully; foaming was an important, but not essential, factor.