148 LUNG FLUID IN HYPOXIC LAMBS

Abstract

In newborn lambs, alveolar hypoxia for 3-6 h increases filtration pressure in the pulmonary microcirculation and drives fluid into the lungs: pulmonary lymph flow increases and the concentration of protein in lymph decreases (Circ Res 46:111, 1980). To be certain that the increased lymph flow was not simply the result of an acute release of fluid from the lungs, we assessed lung fluid balance in 4 unanesthetized lambs kept hypoxic for 12 h. We used radioactive albumin tracers to see if sustained hypoxia altered microvascular permeability to protein in the lungs. After a 2-4 h control period in air, the lambs breathed 10% O2 and 5% CO2. We measured pressures in the pulmonary artery (Ppa) and left atrium (Pla); lung blood flow (Qb) and lymph flow (Q1); and concentrations of protein in lymph (Lp) and plasma (Pp). During control and experimental periods, we injected 125I-albumin intravenously and determined the time at which specific activity in lymph reached 1/2 that in plasma (T½). Results (X ± sx; *p <.05): In all lambs, Ppa, Qb, and Q1 remained up for the duration of hypoxia; pulmonary vascular resistance increased 62 ± 4%; Lp was persistently low; and T½ did not change. We conclude that prolonged alveolar hypoxia causes a sustained increase in transvascular filtration of fluid into the lungs of lambs; hypoxia does not influence microvascular permeability to protein in the lungs.