Experimental Hydrostatic Pulmonary Edema in Rabbit Lungs: Barrier Lesions

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Abstract
In excised rabbit lungs perfused with a 6% albumin solution, hydrostatic pulmonary edema was induced by moderate (about 14 mm Hg) and high increases (about 29 mm Hg) of capillary transmural pressure. Thereafter, lung tissue and proteinaceous edema fluid were fixed by vascular perfusion and analyzed by electron microscopy for possible lesions of the blood-gas barrier. The following observations appear noteworthy: (1) There were distinct and numerous lesions of the epithelial cell layer. In high-pressure edema, frank disruptions on the thin and thick sides of the blood-gas barrier were prominent. In moderate pressure edema epithelial blebs were more conspicuous. (2) In contrast, endothelial lesions were rare in both high- and moderate-pressure experiments. (3) Epithelial Type I cells revealed an enormous plasticity as illustrated by the formation of large epithelial blebs. (4) Although the entire microvasculature was subjected to high pressures, barrier lesions were exclusively seen in regions with alveolar edema. These findings suggest that barrier leaks play a role in both hydrostatic and permeability lung edema and that the differences between both types of edema rather reflects the type and extent of injury to the alveolar epithelial barrier and the associated inflammatory reaction.