Surface tension induced by dipalmitoyl lecithin in vitro under physiological conditions

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Abstract
The surface tension of 161 films of DPL [dipalmitoyl lecithin] were measured on a Langmuir using a Wilhelmy balance under conditions controlled to simulate the alveolar lining in vivo. The parameters controlled were temperature (maintained at 37.degree. C), humidity (100% at 37.degree. C), surfactant concentrations (encompassing the best available estimates), area changes (consistent with normal respiration), frequency adaptation to continuous cycling and composition and pH of the aqueous hypophase. Simultaneously maintaining these parameters within the best estimates of physiological limits, the relationships between surface tension and surface area showed appreciable differences from previous studies, present results showing higher minimum values of surface tension, appreciably less change in surface tension with compression and far less hysteresis between surface tension and surface area. The higher minimum values are consistent with original estimates of alveolar surface tension, i.e., 35-41 dyne cm-1. Although appreciably smaller than previously reported, the change in surface tension with change in area is adequate to impart alveolar stability. The reversibility between surface tension and surface area under physiological conditions is discussed in relation to compliance hysteresis which is considered to be more dependent upon geometric irreversibility of the alveolar surface than upon any intrinsic property of the surfactant.

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