DYNAMIC SURFACE-TENSION AND SURFACE-AREA ELASTICITY OF ADSORBED PULMONARY SURFACTANT LAYERS

The mechanical surface properties of adsorbed artificially (bronchoalv eolar lavages) as well as naturally produced (breathing condensate) lu ng surface-active materials were investigated by measuring dynamic sur face tension and surface dilational elasticity. Surface tension was de termined 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. T he transport process of the lung surfactants to the surface seems to o bey a mechanism which can be described by two different time constants . Surface elasticity was measured by three different methods: the osci llating bubble, the oscillating barrier and the oscillating meniscus t echnique. The results of the surface elasticity obtained by the first two methods are rather high whereas those obtained by the third are di stinctly lower. The role of surface elasticity in lung function in com parison with static surface tension is discussed. As the effect of sur face elasticity on the capillary pressure of an alveolus is opposite t o that of the static surface tension, it is concluded that it is high surface elasticity rather than very low surface tension which is decis ive for normal lung function. The surface properties of the lung surfa ctants obtained from the three different sources do not differ from ea ch other in principle. Emphasis is also put on the necessity of taking into account more carefully the boundary conditions of the measuring techniques applied.