ROLE OF PULMONARY SURFACTANT IN AIRWAY-CLOSURE - A COMPUTATIONAL STUDY

A numerical model that simulates airway closure by liquid bridging dur ing expiration has been developed. The effects of both surfactant and time-varying geometry have been included; the model determines the liq uid layer flow resulting from a surface tension (Rayleigh) instability , and the computation traces the film's development to closure, yieldi ng pressure, velocity, surface shape, and surfactant concentration dis tributions. It is found that surfactant is effective in retarding or e liminating liquid bridging through the reduction of the mean surface t ension and the action of surface tension gradients. The former effect is also critical in minimizing the magnitude of the negative pressure in the liquid layer and thus presumably in reducing the tendency for a irway compliant collapse.