COMPUTATIONAL FLUID DYNAMICS SIMULATIONS OF INSPIRATORY AIRFLOW IN THE HUMAN NOSE AND NASOPHARYNX

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Abstract
Extrapolation of the regional dose of an inhaled xenobiotic from laboratory animals to humans for purposes of assessing human health risk is problematic because of large interspecies differences in nasal respiratory physiology and airway anatomy. There is a need for dosimetry models that can adjust for these differences in the upper respiratory tract. The present work extends previous efforts in this laboratory and elsewhere to simulate nasal airflow profiles numerically in laboratory animals and humans. A three-dimensional, anatomically accurate representation of an adult human nasal cavity and nasopharynx was constructed. The Navier-Stokes and continuity equations for airflow were solved using the finite-element method under steady-state, inspiratory conditions simulating rest and light exercise (steady-state inspiratory flow rates: 15 L/min and 26 L/min, respectively) with the fluid dynamics software package FIDAP. Simulated airflow was streamlined in the main nasal passages and complex in the vestibule and nasopharynx. Swirling air currents and recirculating flow were predicted in the nasal vestibule, and the expansion at the nasopharynx gave rise to two downward, countercurrent, spiraling vortices. Significant lateral flow was observed mainly in the middle lateral meatus. Flow apportionment among different regions of the nose remained almost unchanged between the two inspiratory rates simulated. Fastest flow occurred in the posterior nasal valve region. In the main nasal airway, the highest airspeeds occurred through the ventral and middle medial regions. Simulated velocity fields and pressure drops across the nasal cavity generally agreed with experimental results from the literature. It is proposed that this model can be used to reduce uncertainty in human health risk assessment for inhaled materials and to assess changes in airflow and nasal resistance due to common surgical procedures and medical conditions.