Numerical simulation of ozone transport and uptake in asymmetrically-branched airways of the respiratory tract

The pattern of lung injury induced by the inhalation of reactive gases such as O₃, a ubiquitous air pollutant, is believed to depend on the dose delivered to different tissues in the respiratory tract. To test this hypothesis, numerical simulations of ozone transport and uptake in anatomically-correct geometries of the conductive airways of a Rhesus monkey were conducted. The airway geometry was created using three-dimensional reconstruction of the tracheobronchial tree from MRI images of the lung, and an unstructured volume mesh was generated for the first few generations of the resulting branched structure. Three-dimensional numerical solutions of the Navier-Stokes, continuity, and species convection-diffusion equations subject to a surface reaction wall condition were subsequently obtained for steady inspiratory and expiratory flows at physiologically relevant Reynolds number ranging from 100 to 500. An effective rate constant for the surface reaction was formulated based on a quasi-steady diffusion-reaction analysis in the epithelial lining fluid. The total rate of O₃ uptake within each generation was determined, and hot spots of O₃ flux on the airway walls were identified. Spikes in O₃ flux appeared downstream of the first bifurcation. Results of the three-dimensional simulations for O₃ uptake along a single asymmetrically-branched airway path were also compared to the predictions of an axisymmetric single-path model. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).