Abstract
Pulmonary edema which occurs in the collapsed lung after reexpansion, is known as reexpansion pulmonary edema. However, the precise pathogenesis of this type of pulmonary edema has not been determined. Three experiments were performed in awake sheep with chronic lymph fistulae: control (n=4), 2-hour lung collapse (n=4) and 24-hour lung collapse (n=4). In the control experiment, lung lymph flow, lymph-to-plasma protein concentration ratio (L/P ratio), hemodynamics and blood gases did not change. In the 2-hour lung collapse experiment, lymph flow and the L/P ratio did not change during lung collapse or after the lung reexpansion. The pulmonary arterial pressure increased and the arterial oxygen tension decreased significantly during lung collapse. Reexpansion caused a return to baseline values. In the 24-hour lung collapse experiment, the lymph flow increased remarkably after the reexpansion. The L/P ratio increased 24 hours after the lung collapse and remained at a still higher level than baseline after the lung reexpansion. The pulmonary arterial pressure was about 5cmH2O higher than baseline and did not decrease after reexpansion, unlike that of the 2-hour collapse experiment. From these experiments, we conclude that long term lung collapse and reexpansion does cause pulmonary microvascular injury and permeability edema.
