| The capillary instability that occurs on an annular film lining a tube is studied as a model of airway closure, through bench top experiments, to determine the effects of surfactant and film thickness. An annular film is formed by infusing water into an oil-filled capillary tube. Surface waves grow with time and eventually cause a liquid bridge across the tube. The initial instability growth rate and closure time are measured for a range of film thicknesses between 12 and 36% of the tube radius. Thicker films increase the growth rate and decrease closure time. Surfactant decreases the growth rate to 20% and quadruples the closure time.;A liquid plug may be present in an airway due to disease, airway closure, or by instillation during medical therapies. Forced air propagates the plug through the airways, depositing a film onto the walls. Bench-top experiments are conducted to investigate liquid plug flow corresponding to four situations that the plug may encounter. In Case (i), straight dry tubes, the plug deposits a film onto the tube walls, with the film thickness related to Ca. In Case (ii), tubes with a preexisting liquid film, the trailing film may be thinner or thicker than the precursor, depending on Ca. In Case (iii), bifurcating tubes, the plug propagates in the parent tube and divides evenly between the daughters. In Case (iv), bifurcating tubes with a liquid blockage in one daughter, the plug divides unevenly. Nearly twice as much plug fluid enters the unblocked daughter as the blocked, and then travels with a greater speed.;An animal lung model is also used to investigate the dynamic transport and distribution of instilled liquid throughout the airways. A radio-opaque surfactant mixture is instilled into the trachea of vertical, excised rat lungs during constant ventilation. The liquid either forms a plug in the trachea, or partially drains due to gravity, before each inspiration. X rays of the surfactant progression are recorded at 30 frames/sec, digitized and processed to determine the distribution in the lungs. Formation of a liquid plug is key for uniform distribution, and increases the homogeneity of distribution. |
