COMPUTATIONAL FLUID-DYNAMICS SIMULATIONS OF INSPIRATORY AIR-FLOW IN THE HUMAN NOSE AND NASOPHARYNX

Extrapolation of the regional dose of an inhaled xenobiotic from labor atory animals to humans for purposes of assessing human health risk is problematic because of large interspecies differences in nasal respir atory physiology and airway anatomy. There is a need for dosimetry mod els that can adjust for these differences in the upper respiratory tra ct. The present work extends previous efforts in this laboratory and e lsewhere to simulate nasal airflow profiles numerically in laboratory animals and humans. A three-dimensional, anatomically accurate represe ntation of an adult human nasal cavity and nasopharynx was constructed . The Navier-Stokes and continuity equations for airflow were solved u sing the finite-element method under steady-stale, inspiratory conditi ons simulating rest and light exercise (steady-state inspiratory flow rates: 15 L/min and 26 L/min, respectively) with the fluid dynamics so ftware package FIDAP. Simulated airflow was streamlined in the main na sal passages and complex in the vestibule and nasopharynx. Swirling ai r currents and recirculating flow were predicted in the nasal vestibul e, and the expansion at the nasopharynx gave rise to two downward, cou ntercurrent, spiraling vortices. Significant lateral flow was observed mainly in the middle lateral meatus. Flow apportionment among differe nt regions of the nose remained almost unchanged between the two inspi ratory rates simulated. Fastest flow occurred in the posterior nasal v alve region. In the main nasal airway, the highest airspeeds occurred through the ventral and middle medial regions. Simulated velocity fiel ds and pressure drops across the nasal cavity generally agreed with ex perimental 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 resistan ce due to common surgical procedures and medical conditions.