INCORPORATION OF NASAL-LINING MASS-TRANSFER RESISTANCE INTO A CFD MODEL FOR PREDICTION OF OZONE DOSIMETRY IN THE UPPER RESPIRATORY-TRACT

Inhalation of ambient concentrations of ozone ia strong oxidant) has b een reported to injure regions of the monkey and rat upper respiratory tract (URT) that contain little intraepithelial mucosubstances (regio ns lined by transitional epithelium) and to spare adjacent regions tha t contain abundant stored secretory products (regions lined by respira tory epithelium). II is therefore hypothesized that mucus provides a m ajor resistance to ozone mass transport in the URT. As part of a large r project to predict health risks oi inhaled gases, a previously devel oped, computational fluid dynamics (CFD) model oi the Fischer 344 (F34 4) rat nasal passage was modified to describe transport oi ozone. In t his study, mass-transfer resistance in the nasal lining was incorporat ed into the CFD model for prediction of ozone dosimetry. Static mucus and tissue layers were considered. A boundary condition was developed that incorporates mass-transfer resistance in the nasal lining due to one-dimensional diffusion and first-order reaction in the mucus and ti ssue phases. Physicochemical parameters for ozone were obtained from t he literature. Resistance to mass transfer in the submucosal region (b lood phase) was neglected due to high tissue-phase reactivity (i.e., t he concentration of inhaled chemical in blood was set to zero). To stu dy the possibility that differences in the thickness and/or quality (v ariation in physico-chemical properties) of mucus coating the transiti onal and respiratory epithelium account for reported patterns of injur y, a simulation was performed into which regional differences in mucus thickness were incorporated. Results suggest that mass-transfer resis tance in the mucus phase is important for describing ozone dosimetry i n the URT. In addition, mucus thickness may play a role in determining the pattern of ozone-induced nasal lesions.