'De-watering' capabilities of surfactants in human amniotic fluid.

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Abstract
The phospholipid extracts from each of 11 samples of human amniotic fluid obtained from 11 full-term births were deposited as oriented monolayers adsorbed to glass. The surfaces were rendered hydrophilic with maximum contact angles averaging 54.5.degree. while, on withdrawing fluid, the edge of the saline pool receded to expose dry surface with minimum contact angles averaging 15.4.degree.. The extracts were found to be surface-active at the liquid-air interface and there was some indication that direct adsorption to solid surfaces was facilitated by Ca ions. In all extracts, a continuous layer of saline adjacent to the adsorbed surface would break up spontaneously to expose dry surface when the thickness was reduced to an average of 764 .mu.m, corresponding to several alveolar diameters. This phenomenon is discussed as a possible means of establishing dry patches on the alveolar membrane, especially in the newborn after the fetal alveolar wall has been exposed to the same surfactants in much the same physical form as found in amniotic fluid. Surfactant adsorbed directly to the tissue subphase is suggested as a physical basis for the discontinuity of the aqueous hypophase seen in many electron micrographs of the adult alveolus. This de-watering of the alveolar surface could facilitate gas transfer.