Surfactant Transport

Surfactant spreading on a thin viscous film supported by a stretchable wall is examined computationally and analytically to study the effects of breathing on surfactant replacement therapy (SRT). We investigate the influence of oscillatory stretch of the finite wall on the spreading of surfactant in the presence of a pre-existing surfactant. The model is developed using lubrication theory, conservation of surfactant and fluid mass, and isotherms for insoluble and soluble surfactants. Numerical solution shows there is an optimal frequency for fastest surfactant spreading for both soluble and insoluble surfactant, suggesting that an optimal breathing frequency for SRT may exist. In addition to the initial transient spreading phase described above, we investigate the mean-steady transport that is responsible for most of the transport in SRT. By reversing the concentration gradient, we investigate surfactant and liquid clearance from the lung. Bench top experiments using a stretchable membrane subjected to oscillatory stretch with an essentially insoluble surfactant confirm the numeric results for the insoluble case. This work supported by NIH grant HL-41126 and NSF grant CTS-9412523.

Transient surfactant spreading with wall stretch. (7.48 MB)

This movie shows a numerical simulation of surfactant spreading on a thin film that is supported by a stretching membrane. The film is initially clean, except for the new surfactant region. The new surfactant begins spreading when the wall stretch starts. A fluid mechanical shock forms near the leading edge of the new surfactant front. The shock is quite steep and the wave appears to break when it reaches the wall of the membrane.