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 thei r particle deposition patterns, Statistical analyses of human and rat tracheobronchial morphometry data have revealed distinct asymmetric fe atures of their airway branching patterns, particularly for the monopo dial 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 ai rflow and aerosol particle trajectories in three-dimensional asymmetri c bifurcation models: (i) the Navier-Stokes equations for the air velo city field are solved by a finite difference volume method, and (ii) t rajectories of aerosol particles entrained in the airstream are simula ted by Monte Carlo techniques. In the present paper, the effects of in terspecies differences in particle deposition patterns are explored fo r two typical bifurcation geometries in segmental bronchi (generations 4-5) and terminal bronchioles (generations 15-16) of the human and ra t lungs for inspiration as well as expiration. The observed interspeci es differences in localized particle deposition patterns and related d eposition efficiencies demonstrate that the respective morphometric as ymmetries in airway branching are a major determinant of the local dis tributions of deposited particulate matter in bronchial airway bifurca tions.