Surfactant - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 797

can be removed. Alveolar type-2 cells can ensure surfactant clearance and recycle a
fraction upon secretion. A surfactant amount is taken up by alveolar macrophages,
in adition to bronchial Clara cells. The transport of liquid and insoluble surfactant
through airways from a source located at the tracheal end was computed [ 1619 ].
Its transit time is strongly influenced by the concentration of pre-existing surfactant
and airway geometrical properties.
The effect of in-plane wall oscillations on surfactant transport in a thin fluid
film on a membrane to mimic airway wall motion was studied in a 3-bifurcation
airway tree model [ 1618 ]. Walls covered by a pre-established liquid film thickness
and a steady-state surfactant concentration (background surfactant transport) were
subjected to cyclic stretches with variable amplitude and frequency. The surface
tension is related to the surfactant concentration by a linear equation of state. The
flux of soluble surfactant between from the bulk (thin fluid film) and interface is
computed using a linear sorption interfacial kinetics equation. Surfactant transport
is enhanced at large stretching cycle amplitudes. The amplitude being constant, high
stretching cycle frequency improves and attenuates surfactant transport at small and
large amplitudes, respectively.