Dynamic surface tension properties of mixed lecithin-cholesterol films related to the respiratory mechanics.

A bubble method was used to record dynamic area/surface tension diagrams of mixed lecithin-cholesterol films prepared at different weight ratios. The lecithin/cholesterol weight ratios were: 1:2, 1:1, 4:1, 6:1, 8:1 and 12:1. The minimum surface tension is about 20 dyn/cm for all weight ratios at amplitudes of 75, 25, 12.5, 6 and 3% area oscillation. The maximum surface tension depends on both the amplitude of area oscillation and the lecithin/cholesterol weight ratio. The maximum surface tension increases with increasing amplitude. At the amplitudes 25, 12.5, 6 and 3% the maximum surface tension is significant higher at the weight ratios 1:2 and 1:1 compared to the other ratios. In addition, equilibrium surface tensions during interruptions of the oscillation at maximum and minimum area were recorded. The equilibrium surface tension increases with increasing amplitude up to 25% area oscillation. A static hysteresis seems to remain. Some consequences regarding the pulmonary respiratory mechanics are discussed.