Water repellency induced by pulmonary surfactants.

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Abstract
Pure cotton fabric was partially carboxylated to produce a tough, porous, hydrophilic subphase to simulate the epithelial membrane of the alveolar wall from a permability standpoint. Two of the predominant pulmonary surfactants, dipalmitoyl lecithin (DPL) and dipalmitoyl phosphatidylethanolamine (DPPE), inhibited wetting of this synthetic membrane and of human cutaneous epithelium as manifested by a large contact angle. When treated with DPL at physiological concentrations, the porous synthetic membrane supported a head of saline well in excess of systolic pulmonary artery pressure with no penetration and could do so for periods well in excess of 1 h; untreated control samples allowed almost immediate fluid filtration. Filtration could be initiated in the DPL-treated membranes by wetting the reverse side, confirming that the threshold pressure for fluid penetration was afforded by capillarity and, by water repellency induced by the surfactant. Water repellency induced by the amphoteric surfactants occurring naturally in the lung is discussed as a possible factor contributing to the pressure threshold to be exceeded for alveolar edema to form. Evidence is reviewed and several advantages discussed for the implied concept of an essentially dry lining to the alveolus with a discontinuous liquid layer largely confined to convex corners, which could slowly resolve any edema by surface forces.

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