Pulmonary interstitial edema in the isogravimetric perfused canine lung produced by venous constriction results in decreased compliance and pulmonary venous PO2, and increased pulmonary capillary pressure. Release of venous constriction is associated with further deterioration in pulmonary venous PO2, and no improvement in lung weight or compliance although PCi returns toward normal. Addition of 15 grams LMW dextran minimizes the fall in PVO2 and shows less perivascular edema microscopically, but does not otherwise differ from untreated controls. In contrast, deleterious effects are noted after the addition of 1.5 grams mannitol shown by marked weight gain, increased PCi, decreased PVO2, and decreased compliance. In addition, electron microscopy shows focal endothelial cell damage and more marked perivascular space edema. The adverse effects of mannitol may relate to its smaller molecular weight facilitating entry into the interstitial space.
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