Physicochemical effects enhance surfactant transport in pulsatile motion of a semi-infinite bubble

In this study, we investigate the sorption of pulmonary surfactant (Infasurf, Ony, Buffalo, NY) occurring at the air-liquid interface of a semi-infinite finger of air as it oscillates and progresses along a small rigid tube (1 mm inner diameter) occluded with a surfactant-doped solution of concentrations C=0.1, 0.05, or 0.01 mg/mL. This simple experimental model of pulmonary airway reopening is designed to examine how altering the fluid flow field may lower reopening pressures and lead to a reduction in airway wall damage that is associated with the mechanical ventilation of an obstructed pulmonary system in airways of the deep lung with depleted endogenous and little exogenous surfactant. We analyzed a range of pulsatile flow scenarios by varying the oscillation frequency (0< or =f < or =1 Hz), the oscillation flow waveform, and the steady flow rate (Q(steady)=0.1 or 0.01 mL/min). These experimental studies indicate that a high frequency (1 Hz, amplitude = 5 mm), fast-forward oscillation waveform superimposed onto a fast steady flow (0.1 mL/min) substantially reduces mean reopening pressures (31%) as a consequence of the modified flow field and the commensurate increase in surfactant transport and adsorption. This result suggests that imposing high frequency, low amplitude oscillations during airway reopening will help to diminish ventilator-induced lung injury.