Mechanical stresses associated with airway reopening injury of pulmonary epithelial cells

Repetitive airway collapse and reopening subjects the pulmonary epithelium to large, dynamic, and potentially injurious mechanical stresses. A narrow fluid-occluded channel was used as an idealized model of a collapsed segment of an airway where the walls are held in opposition by a viscous fluid. For saline-occluded channels, bubble progression produced significantly increased numbers of injured cells when compared to the control. The addition of Infasurf (1 mg/mL) to the occlusion fluid reduced the number of injured cells to a level similar to the Control. Fluid dynamic simulations reveal that the hydrodynamic environment of the cells in the experimental model is complex and suggested that different components of the stress cycle associated with airway reopening - shear stress, the shear stress gradient, or the pressure gradient - may be injurious. From these simulations, we concluded that the most likely mechanically damaging element of stress cycle associated with bubble progression was the steep pressure gradient.