Abstract
Liquid plug flow through tubes and the associated liquid film deposition play an important role in several applications, including medical procedures, coating industry, chemical processing, etc. The aim of this research is to improve the effectiveness of surfactant replacement therapy (SRT) in treating preterm infants with respiratory distress syndrome (RDS) through computational simulations. RDS is caused by a pulmonary surfactant deficiency in preterm infants, causing breathing difficulties and atelectasis, which, unfortunately, is the leading cause of mortality in preterm infants. The most common treatment procedure is SRT, which seeks to replace the missing surfactant in the infant's lung, with the ultimate goal of achieving uniform film distribution and reaching the alveoli at the terminating branches of the airway. Although, relatively effective, SRT has a 35 non-response rate. The low response rate is attributed to the complexity of the human lung, spanning 15 continuously-branching airway tubes, which successively become narrower, shorter and more numerous. The surfactant delivery mechanism is governed by the fluid dynamics of plug ow in each airway. As a result and given the complex geometry of the lung, it is extremely difficult for medical practitioners to achieve uniform surfactant distribution throughout the airway tree. We seek to better understand the fluid dynamics of surfactant plug transport to resolve non-uniform surfactant distribution in the lung. We present 3D CFD simulations of plug motion in straight and bifurcating tubes with pre-wetted walls for a range of capillary numbers. The bifurcating tubes follow the geometries of the two- and three-generation lung airway models. The pre existing film is differentiated from the deposited film by using a passive scalar that tags the liquid plug allowing for accurate quantification of transient film deposition. We study the temporal and spatial variation of the deposited film thickness, and show its dependency on pre-existing film thickness and interplay between gravity and plug inertia. Additionally, we present 3D simulations of plug splitting in bifurcating tubes at various roll angles, where one daughter tube is gravitationally favored. The plug re-orientation in the bifurcation zone and the subsequent impact on asymmetric plug splitting is elucidated for the first time. Our preliminary results suggest a new surfactant delivery strategy using multi-plug aliquot delivery. The proposed strategy can potentially overcome the effects that lead to asymmetric film distribution in the airway. Compared to the traditional method of single dose instillations, the proposed strategy shows improvement in the overall homogeneity of surfactant delivered into the lung.