Airway reopening mechanics
The introduction of air to a neonate's lungs and the reopening of an occluded airway are events where liquid-lining flows and interfacial phenomena can be physiologically significant. To (re)open an occluded airway, a long air bubble must propagate through the collapsed airway and separate the walls. On its first breath, a surfactant-deficient (SD) neonate may have trouble creating the substantial pressures needed to fully inflate the lung against the high surface tension at the surfactant-depleted air-liquid interface. Surfactant is vital for healthy normal breathing, and keeps the surface tension of the lung relatively low. When an SD-neonate's lungs are inflated, either through the infant's own effort or mechanical ventilation, surfactant deficiency or tissue compliance may cause mechanical instability that could lead to airway closure. This may further result in atelectasis and thus decreased lung volume and hypoxemia.
Recently, together colleagues at Tulane University, I have explored the importance of liquid lining flows and interfacial phenomena on reopening behavior. These studies have been used to investigate the macroscopic phenomena that determine reopening pressures, and micromechanical events that establish the mechanical stresses that can occur at the cellular level. We have also looked at the influence of surfactant. The main goal has been to investigate the importance of surfactant physicochemical properties during steady and unsteady opening of pulmonary airways. Perturbation and computational techniques can be used to solve coupled free surface boundary value problems. A list of relevant publications is given below.
Halpern, D. and Gaver, D.P. Boundary element analysis of two-phase displacement in a Hele-Shaw cell. J. Comp. Phys. 115(2): 366-375, 1994. Abstract Article (PDF 466K)
Gaver, D.P. III, Halpern, D., Jensen, O.E. & Grotberg, J.B. The Steady motion of a Semi-Infinite Bubble Through a Flexible-Walled Channel. J. Fluid Mech. 319: 25-45, 1996. (Abstract).
Ghadiali, S.N. , Halpern, D. and Gaver, D.P. A dual-reciprocity boundary element method for evaluating bulk convective transport of surfactant in free surface flows. J. Comp. Phys. 171: 534-559, 2001. Abstract | References Article (PDF 373K)
Halpern, D. and Jensen, O.E. A semi-infinite bubble advancing into a planar tapered channel. Phys. Fluids. 14(2), 431-442, 2002.< o:p> PDF (168 kB) GZipped PS Order.
Jensen, O.E., Horsburgh, M.K., Halpern, D. & Gaver, D.P. III The steady propagation of a bubble in a flexible-walled channel: asymptotic and computational models. Phys. Fluids. 14(2), 443-457, 2002. PDF (217 kB) GZipped PS Order.
Halpern, D., Naire, S., Jensen, O.E. & Gaver, D.P. III Unsteady bubble propagation in a flexible-walled channel: predictions of a viscous stick-slip instability.J. Fluid Mech. 528, 53-86,2005. [abstract] [PDF]
Halpern, D. and Gaver, D.P. The influence of surfactant on the propagation of a semi-infinite bubble through a liquid filled compliant channel. J. Fluid Mech. 698, 125-159, 2012.
Fujioka, H., Halpern, D., and Gaver, D.P. A model of surfactant-induced surface tension effects on the parenchymal tethering of pulmonary airways. J. Biomechanics 46, 319-328, 2013.
Ryans, J., Fujioka, H., Halpern, D.and Gaver, D.P. Reduced-dimension modeling of recruitment/de-recruitment dynamics of the lung. Ann. Biomed. Eng. doi:10.1007/s10439-016-1672-9, 2016.
Fujioka, H., Halpern, D., Ryans, J. and Gaver, D.P. Reduced-dimension model of liquid plug propagation in tubes. Phys. Rev. Fluids, 1(5), 053201, doi: 10.1103/ Phys Rev Fluids.1.053201, 2016.