Numerical modeling of airflow and mass transfer in the human nasal cavity

The nasal physiological functions of pollutant filtration and olfaction are dependent on airflow and mass transport processes. To analyze the transport phenomena, an anatomically correct finite element model of a human nasal cavity was constructed using coronal CAT scan images of a healthy adult nose.;The steady-state equations of motion were solved to determine laminar nasal airflow patterns at quiet breathing flow rates. In the main nasal passages, the highest air speed occurred along the nasal floor and a second lower peak occurred between the inferior and middle turbinates. The air-stream entering the anterior tip of the naris traveled to the olfactory slit, without forming separated recircultating zones. About 10% of the inspiratory volumetric flow passed through the olfactory airway, and remained nearly constant with variation in flow rate. The numerical velocity field was validated by comparison with experimentally measured velocities in a large scale physical model, that was built by scaling up from the same CAT scans.;The uncoupled convective-diffusion equation was solved using the velocity field, to determine uptake of inhaled vapors and ultrafine particles. A wall boundary condition was developed that included the effects of vapor solubility in a mucus layer, diffusion and chemical reaction in the mucus, and epithelial membrane permeability. The maximum absorption efficiency (fractional uptake) of the nasal cavity, up to the posterior end of the turbinates, was about 80%. The maximum flux in the main nasal passages occurred on the anterior-inferior end of the middle turbinate, which is a common location for pollutant-induced nasal lesions.;The mass transfer model was used to determine uptake of inspired odorants on the olfactory mucosa. Total olfactory flux, that is correlated with perceived odor intensity, was less than 5% of total flux over the entire nasal surface. Different odorants generated discernibly different flux patterns across the olfactory mucosa, that may serve to encode odor quality. Total, peak, and patterns of flux, on the olfactory mucosa and the entire nasal surface, were dependent on the physiochemical properties of the inhaled spices (which determine the wall boundary condition) and the nasal flow rate.