Computation of local enhancement factors for the quantification of particle deposition patterns in airway bifurcations

Spatial deposition patterns in two different geometric models of bronchial airway bifurcations were computed by solving numerically the 3D Navier–Stokes equations and simulating particle trajectories under the simultaneous action of impaction, sedimentation, diffusion, and interception by Monte Carlo techniques. To quantify the inhomogeneities of the predicted deposition patterns the whole surface of the bifurcation was scanned with a prespecified surface area element to determine the number of particles deposited per unit surface area. The local deposition density in a given surface element, relative to the average deposition density, was then defined as the local deposition enhancement factor. In the present study, the computation of local deposition enhancement factors focused on inspiratory particle deposition patterns. Our results revealed that the distributions of local deposition enhancement factors along the surface of a bifurcation exhibit strong inhomogeneities for all particle sizes and bifurcation geometries considered here. The maximum enhancement factor in a bifurcation was found to be about 100 in the upper bronchial airways for any particle size in the diameter range from 0.01 to 10 μm, obtained with a 100 μm×100 μm scanning element. These numerically computed local deposition enhancement factors can be directly applied to inhalation health effect protocols to consider the effects of highly localized doses.