ALVEOLAR EPITHELIAL FLUID CLEARANCE MECHANISMS ARE INTACT AFTER MODERATE HYPEROXIC LUNG INJURY IN RATS

The capacity of the alveolar epithelial barrier to remove excess alveo lar fluid from the airspaces of the lung was studied in an experimenta l model of moderate hyperoxic lung injury. Rats were exposed to 100% o xygen for 40 h in an exposure chamber and compared with control animal s exposed to room air, Extravascular lung water was calculated gravime trically, Alveolar and lung liquid clearance were studied over 1 h by instillation of a 5% albumin solution with 1.5 mu Ci of I-125-labeled albumin (6 mL/kg into both lungs), The concentration of both the unlab eled and labeled albumin was used to calculate alveolar liquid clearan ce, Hyperoxic rats developed pulmonary edema, with a 33% increase in e xtravascular lung water to 5.3+/-0.1 g of water pel gram of dry lung, compared with 4.0+/-0.2 g of water per gram of dry lung in control rat s (p<0.05). This degree of edema was associated with a significant inc rease in the alveolar-arterial oxygen difference (241+/-61 vs 124+/-14 mm Hg in control animals exposed to room air, p<0.05). Despite this m oderate degree of lung injury, alveolar fluid clearance was normal (30 +/-3%) compared with control rats (33+/-6%). Furthermore, the hyperoxi c injured rats responded normally to an exogenous beta-adrenergic agon ist (terbutaline, 10(-4) mol/L) with a 67% increase in the rate of alv eolar liquid clearance (50+/-5%). Thus, in the setting of moderate hyp eroxic lung injury, the alveolar epithelial barrier is still capable o f removing fluid at a normal rate and responding to P-adrenergic agoni st treatment, These experimental results have potential clinical impli cations for patients with acute lung injury.