We measured the protein composition of plasma and lung fluids from nine dogs with cardiogenic edema. To produce the edema, we increased left atrial pressure an average of 36 cmH2O by inflating a balloon catheter in the left atrium, infusing norepinephrine, and infusing large volumes of saline or saline-diluted blood. Blood samples were collected every 15 min, and airway fluid was collected from five dogs that developed severe edema. Terminally, the chest was opened and the lungs were removed. Samples of alveolar fluid were taken from the excised lung by direct pleural puncture with micropipettes. The lungs were frozen in liquid nitrogen and samples of free interstitial fluid were taken from the perivascular and peribronchial cuffs. Plasma and lung fluids were analyzed for total protein by the Lowry method and for albumin-globulin fractions by cellulose acetate electrophoresis. The average total protein concentrations (g/100 ml) were--plasma, 2.65; free interstitial fluid, 1.05; alveolar fluid, 1.23; and airway fluid, 1.29. The average albumin fraction of plasma was 0.40; of alveolar fluid, 0.43; and of airway fluid, 0.43. The protein concentrations in the three lung fluids were nearly identical to each other, but were less than half that of plasma. We conclude that in high-pressure pulmonary edema with alveolar flooding, the capillary endothelium retains the ability to restrict protein relative to fluid filtration, but the alveolar epithelium becomes freely permeable to protein.

In 11 anesthetized dogs with acute alloxan-induced pulmonary edema, we measured the protein composition of 1-mul samples of plasma, free interstitial fluid, alveolar fluid, and airway fluid. We obtained plasma and airway fluid at regular intervals as edema developed. We sampled alveolar fluid by pleural micropuncture in the unfrozen, excised lung and free interstitial fluid from perivascular cuffs in the frozen, excised lung. The average (+/- 1 SD) total protein concentration of plasma was 4.9 +/- 0.6, airway fluid 4.4 +/- 0.7, free interstitial fluid 4.9 +/- 0.7, and alveolar fluid 5.2 +/- 0.8 g/100 ml. The average fractions of albumin were 0.42 +/- 0.05, 0.50 +/- 0.05, 0.49 +/- 0.06, and 0.49 +/- 0.07, respectively. By paired analysis, the protein concentration of interstitial fluid was not significantly different from alveolar fluid. The protein concentration of airway fluid was significantly less than that in interstitial and alveolar fluid. The albumin fraction of the three lung fluids was identical but significantly different from plasma. We conclude that in alloxan-induced pulmonary edema the lung fluids contain high concentrations of protein and the alveolar epithelial membrane becomes freely permeable to protein molecules.