Dynamic surface tension and surface area elasticity of adsorbed pulmonary surfactant layers

Abstract

The mechanical surface properties of adsorbed artificially (bronchoalveolar lavages) as well as naturally produced (breathing condensate) lung surface-active materials were investigated by measuring dynamic surface tension and surface dilational elasticity. Surface tension was determined by applying the modified ring and Wilhelmy plate method. The lowest surface tension values observed were not lower than 25 mN m −1. Values like these are characteristic of “classical” surfactants. The transport process of the lung surfactants to the surface seems to obey a mechanism which can be described by two different time constants. Surface elasticity was measured by three different methods: the oscillating bubble, the oscillating barrier and the oscillating meniscus technique. The results of the surface elasticity obtained by the first two methods are rather high whereas those obtained by the third are distinctly lower. The role of surface elasticity in lung function in comparison with static surface tension is discussed. As the effect of surface elasticity on the capillary pressure of an alveolus is opposite to that of the static surface tension, it is concluded that it is high surface elasticity rather than very low surface tension which is decisive for normal lung function. The surface properties of the lung surfactants obtained from the three different sources do not differ from each other in principle. Emphasis is also put on the necessity of taking into account more carefully the boundary conditions of the measuring techniques applied.