Application of computational fluid dynamics to regional dosimetry of inhaled chemicals in the upper respiratory tract of the rat.

For certain inhaled air pollutants, such as reactive, water soluble gases, the distribution of nasal lesions observed in F344 rats may be closely related to regional gas uptake patterns in the nose. These uptake patterns can be influenced by the currents of air flowing through the upper respiratory tract during the breathing cycle. Since data on respiratory tract lesions in F344 rats are extrapolated to humans to make predictions of risk to human health, a better understanding of the factors affecting these responses is needed. To assess potential effects of nasal airflow on lesion location and severity, a methodology was developed for creation of computer simulations of steady-state airflow and gas transport using a three-dimensional finite element grid reconstructed from serial step-sections of the nasal passages of a male F344 rat. Simulations on a supercomputer used the computational fluid dynamics package FIDAP (FDI, Evanston, IL). Distinct streams of bulk flow evident in the simulations matched inspiratory streams reported for the F344 rat. Moreover, simulated regional flow velocities matched measured velocities in concurrent laboratory experiments with a hollow nasal mold. Computer-predicted flows were used in simulations of gas transport to nasal passage walls, with formaldehyde as a test case. Results from the uptake simulations were compared with the reported distribution of formaldehyde-induced nasal lesions observed in the F344 rat, and indicated that airflow-driven uptake patterns probably play an important role in determining the location of certain nasal lesions induced by formaldehyde. This work demonstrated the feasibility of applying computational fluid dynamics to airflow-driven dosimetry of inhaled chemicals in the upper respiratory tract.