Surfactant transport on highly viscous surface films

Abstract

We examine surfactant transport on a highly viscous film overlying a much less viscous layer, aimed at situations within the smaller pulmonary airways, wherein the highly viscous film corresponds to the mucus layer, that rides atop the Periciliary liquid layer (PCL). To this end, we generate a variant of the lubrication approximation by promoting terms which would have otherwise been neglected within standard lubrication theory; this is reminiscent of theories involving free films, viscous jets and threads. We also account for the presence of van der Waals forces, which could rupture the thin bilayer fluid coating the small airways. This is a potential difficulty for surfactant replacement therapy (SRT) since rupture will leave behind pools of stranded surfactant thereby restricting the levels reaching the smallest airways and potentially leading to clinical failure. In the present study, the presence of the mucus for a wide range of system parameters using analytical techniques and numerical simulations.