The significance of particle deposition patterns in bronchial airway bifurcations for extrapolation modeling

The validity of extrapolating rat deposition data to human inhalation conditions depends on the degree of similarity (or difference) of their particle deposition patterns, Statistical analyses of human and rat tracheobronchial morphometry data have revealed distinct asymmetric features of their airway branching patterns, particularly for the monopodial branching structure of the rat lung. Our predictions of particle deposition patterns within asymmetric bronchial bifurcations in human and rat lungs are based on a numerical model for the calculation of airflow and aerosol particle trajectories in three-dimensional asymmetric bifurcation models: (i) the Navier-Stokes equations for the air velocity field are solved by a finite difference volume method, and (ii) trajectories of aerosol particles entrained in the airstream are simulated by Monte Carlo techniques. In the present paper, the effects of interspecies differences in particle deposition patterns are explored for two typical bifurcation geometries in segmental bronchi (generations 4-5) and terminal bronchioles (generations 15-16) of the human and rat lungs for inspiration as well as expiration. The observed interspecies differences in localized particle deposition patterns and related deposition efficiencies demonstrate that the respective morphometric asymmetries in airway branching are a major determinant of the local distributions of deposited particulate matter in bronchial airway bifurcations.