ABSTRACT
I. Introduction Studies of epithelial fluid transport by the distal pulmonary epithelium have provided important new insights into the resolution of acute pulmonary edema, a common clinical problem. For many years, it was believed that differences in hydrostatic and protein osmotic pressures (Starling forces) accounted for the removal of excess fluid from the airspaces of the adult lung. Until the early 1980s, there were no satisfactory adult animal models to study the resolution of alveolar edema, and the isolation and culture of alveolar epithelial type II cells was just becoming a useful experimental method. In the early 1980s, new work provided evidence that fluid balance in the lung was regulated by active ion transport mechanisms (1-3), setting the stage for a rapid advance in our understanding of lung epithelial ion and fluid transport. This chapter discusses the regulation of lung fluid balance by active transport mechanisms across both the alveolar and distal airway epithelium of the mature lung, in both animals with conditions resembling acute lung injury or respiratory distress syndrome and in patients with acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and cardiogenic pulmonary edema. Some of the information and perspectives in this chapter has been included in a recent review (4) and in a prior version of this chapter (5). Another recent review by Davis and Matalon (6) focuses on recent advances in the function of sodium and fluid transport under pathological conditions. A review of fetal and newborn lung fluid balance is beyond the scope of this chapter, although several excellent articles by Strang, Olver, Walters, Bland, and other investigators are available (7-9).
