An experimental model investigation of pulmonary airway reopening

Pulmonary airways are fluid lined compliant tubes that are supported by the surrounding parenchymal tissue. In certain diseased states such as emphysema, cystic fibrosis, adult and neonatal respiratory distress syndrome, airways become blocked either by the formation of a liquid meniscus bridge or by the collapse of the airway walls and surrounding parenchyma. The authors designed a benchtop model to mimic the second type of closure by using a collapsed untethered polyethylene tube lined with a Newtonian fluid acting as a viscous adhesive. Downstream of the air-liquid interface (meniscus), the tube was collapsed in a ribbon-like manner, while upstream of the meniscus the tube was constrained to a rectangular cross-section by two sheets of Plexi-glas separated by a distance D. The authors examined how the fluid properties (viscosity, mu , surface tension, gamma , and density, rho ) and the structural characteristics of their model (effective diameter, D, longitudinal tension, T, and fluid film thickness, H) affected the opening of the tube. D, T, and H corresponded to relevant physical conditions in the lung.