Analysis of lobar differences in particle deposition in the human lung.

Lung diseases caused by the inhalation of various particulate pollutants have often been reported to occur at specific sites in the lung with some diseases preferentially occurring in one of the lobes. Models for the dosimetry of particulate matter in the lung, therefore, need to be developed at a level of resolution that allows for the study of lobar- and airway-specific patterns of deposition. Using an approach best described as a combination of asymmetric and symmetric approaches to modeling lung geometry, we calculated deposition of particulate matter (PM) ranging from ultrafine to coarse particles in each airway down to the level of the lobar bronchi. Further down the airway tree, we calculated deposition averaged over an airway generation in each lung lobe. We compared our results for regional and lobar deposition with various experimental data as well as with results from other models. The calculated results compared reasonably well with experimental data. Significant variations in deposition were observed among the lobar bronchi as well as among the five lobes. The differences among the lobes were accentuated as one examined generation-specific deposition. Deposition per unit surface area of each lobar bronchus was considerably elevated relative to that calculated for the whole lung. The relative distribution of aerosol deposited per unit surface area among the lobar bronchi was altered by breathing condition and aerosol size. Our observations suggest that a multiple-path model that incorporates the heterogeneous structure of airways in the lung is likely to reduce uncertainties in PM health risk assessments.