Transport of exogenous surfactants on a thin viscous film within an axisymmetric airway

The transport of exogenous surfactant in an axisymmetric pulmonary airway lining is analyzed using the model based on lubrication theory to understand the parameters involved in surfactant replacement therapy for neonatal respiratory distress syndrome, including the ratio of film thickness-to-airway radius ε, and the initial exogenous and endogenous surfactant distributions. Numerical simulation of the model indicates that the film disturbance induced by Marangoni flow in low generation airways (small ε, such as trachea) would be more significant than that in high generation airways (large ε, such as bronchioles) for the same amount of instilled surfactant. The non-dimensional transport properties of the exogenous surfactant, however, are virtually identical in various airway generations considered. Increasing the initial local exogenous concentration enhances the surfactant transport and also intensifies the film disturbance. The presence of endogenous surfactant tends to moderate the shock-like film disturbance and also prolongs the extent of surfactant monolayer front. This, however, does not mean that the spread of exogenous surfactant is enhanced with the presence of endogenous surfactant. The extended monolayer is attributed to the compression of endogenous surfactant concentration in regions ahead of the advancing exogenous surfactant front.