Banafsheh Keshavarzi, The Pennsylvania State University, Department of Chemical Engineering, University Park, PA 16802, James Ultman, Chemical Engineering, The Pennsylvania State University, University Park, PA 16802, and Ali Borhan, Chemical Engineering, Pennsylvania State University, 122 Fenske Laboratory, University Park, PA 16802.
A reproducible pattern of tissue injury induced by inhalation of ozone (O3), a ubiquitous air pollutant, is believed to depend on the local dose delivered to the walls of the respiratory tract. To test this hypothesis, we performed numerical simulations of ozone transport and uptake in an anatomically-correct model of the respiratory tract of a Rhesus monkey. The model geometry was created using three-dimensional reconstruction of MRI images of the respiratory tract, including the nasal passages, the larynx, and the first thirteen generations of the tracheobronchial tree. An unstructured mesh was generated for the resulting structure, and three-dimensional flow and concentration distributions were obtained through numerical solution of the Navier-Stokes, continuity, and species convection-diffusion equations. A quasi-steady diffusion-reaction model was used to account for the interaction between O3 and endogenous substrates in the respiratory tract lining fluid. The total rate of O3 uptake within each section of the respiratory tract was determined, and hot spots of O3 flux on the walls were identified. For steady inspiratory flow under quiet breathing conditions, the predicted location of spikes in O3 flux are consistent with existing experimental observations of the focal sites of epithelial damage in the Rhesus monkey [Postlethwait et al., Am. J. Respir. Cell Molec. Biol. 22:191-199, 2000]. 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.