INTERACTION OF EXOGENOUS AND ENDOGENOUS SURFACTANT - SPREADING-RATE EFFECTS

The spreading rate of an exogenous surfactant monolayer due to surface tension gradients is examined by using our previously reported theore tical analysis, with particular attention given to the effects of endo genous surfactant. It is found that the presence of an endogenous surf actant reduces the spreading rate of exogenous surfactant and that, in certain circumstances, the spreading may be halted. A recently publis hed paper (F. F. Espinosa, A. H. Shapiro, J. J. Fredberg, and R. D. Ka mm. J. Appl. Physiol. 75: 2028-2039, 1993) reaches the opposite conclu sion about the effect of endogenous surfactant, i.e., that the presenc e of an endogenous surfactant increases the spreading rate of the exog enous surfactant. This communication discusses the relevant issues ass ociated with these different results and what the implications may be for surfactant replacement therapy. It is found that the endogenous su rfactant, which is ahead of the advancing exogenous surfactant front, undergoes a concentration increase due to surface area compression of the air-liquid interface. Hence the spreading exogenous surfactant can raise surfactant concentrations in regions distal to its own location , and this is a previously unrecognized potential therapeutic mechanis m of instilled surfactants. After initial instillations of intratrache al boluses of exogenous surfactant, additional surfactant may better r each the desired target site if delivered by aerosol. Predictions of s urfactant and piggy-backed drug-delivery times through the lung are al so discussed.