Recovery from increased pressure or increased leakiness edema in perfused sheep lungs

Two routes by which interstitial pulmonary edema liquid may leave the lung during recovery are reabsorption into the pulmonary circulation and clearance by lung lymphatics. We hypothesized that reabsorption of edema liquid of low protein concentration into the pulmonary circulation would be greater than reabsorption of edema liquid of high protein concentration because of the greater protein osmotic gradient in the former. On the basis of previous studies, lymph flow should contribute minimally to the recovery. In 22 in situ perfused sheep lungs with lymph fistulas, we produced approximately 100 g of osmotic or hydrostatic edema (low protein) or increased leakiness edema by calcium depletion (high protein). To induce reabsorption, we changed the perfusate from low- (1% albumin, osmotic pressure = 4 cmH2O) to high-protein (7% albumin, osmotic pressure = 22 cmH2O) solution in the osmotic group, decreased capillary pressure from 29 +/- 9 to 11 +/- 6 cmH2O in the hydrostatic group, or reversed leakiness by adding CaCl2 to the perfusate in the increased leakiness group. Reabsorption occurred only during recovery from osmotic (40 +/- 22% of filtered liquid) and hydrostatic (15 +/- 11%) edema. Total lung lymph flow during recovery from osmotic, hydrostatic, or increased leakiness edema was 4.9 +/- 3.4, 4.3 +/- 3.4, or 3.5 +/- 1.9 g, respectively. We conclude that during recovery from pulmonary edema interstitial liquid is reabsorbed into the circulation in inverse proportion to its protein concentration. We confirm that only a small fraction of the interstitial edema liquid is cleared by the lymphatics during recovery from any type of edema.