Function of the Alveolar Epithelial Barrier Under Pathologic Conditions

Abstract

T he central importance of the alveolar epithelial barrier in both the pathogenesis and recovery from acute lung injury has only recently been appreciated. In the 10 to 15 years after Petty and Asbaugh’ described the clinical syndrome of the adult respiratory distress syndrome (ARDS),’ most investigators concentrated their efforts on studying mechanisms of lung endothelial injury because injury to the pulmonary vascular barrier was identified as one of the earliest manifestations of acute lung injury. Also, experimental methods were available to measure injury to the lung endothelium. For example, the time course and the severity of lung endothelial injury could be quantified with lung lymph flow studies in sheep or goats,2 and the accumulation of a vascular protein tracer in the extravascular space of the lung could be measured in any species to quantify the extent of lung vascular permeability.3 In many of these studies,considerable attention was given to the interaction of hemodynamic forces and the measured increase in lung vascular permeability.4