Nonlinear simulation of mucociliary clearance: A three- dimensional study

Abstract

In this study three-dimensional (3D) numerical simulation of mucociliary clearance from the lung has been studied. The major thrust of this investigation is 3D simulation of mucociliary clearance accounting for non-linear viscoelastic characteristics of the mucus layer which is one of the most complex fluids in our body. Using a numerical code, three-dimensional unsteady flow computations have been carried out to study ciliary motion in a two-layer fluid model of the (bronchial) airway surface liquid (ASL) consisting of a Newtonian lower periciliary layer (PCL) and a nonlinear viscoelastic upper mucus layer. The projection finite difference method is used to solve the governing and constitutive equations on a staggered Eulerian grid. The immersed boundary method (IBM) is also employed to study the effect of cilia propulsive force on the fluid flow. The 5-mode nonlinear Giesekus model has been used as the constitutive equation of mucus which is characterized by nonlinear (non-Newtonian viscosity) properties. Numerical results have been devoted to study the effect of various parameters such as cilia beat frequency, cilia length as well as PCL and mucus depth on mucociliary clearance. The present 3D model shows very good agreement with previous experimental studies, while ca. 2.5-fold larger clearance rates were found for 2D models. 3D results show that cilia beating frequency and cilia length are the most critical factors affecting mucociliary clearance, while PCL depth and mucus depth have little and intermediate effect on mucus flow and hence clearance rate respectively.