Inclusion of particle dispersion in a rat particle deposition: model improvement and validation.

Deterministic models have been developed for the predictions of the deposited dose to the respiratory tract from inhalation of airborne materials. The complexity of the lung geometry, ventilation mechanics, and transport processes have required model assumptions and simplifications. Model validation is an integral part of the development process before models can be applied to specific scenarios of interest. While several validation efforts have been reported in the literature for regional deposition in the respiratory tract, there is a desire to refine the models to enhance the power of predictions to smaller regions such as per lobe and generation of the respiratory tract. This imperative is contingent on the availability of data. Hence, we refined and validated our lung deposition model developed in rodents by adding additional physical mechanisms missing in the original model. Convective mixing of particles impacts both the distribution and deposited dose of inhaled particles. We developed a semi-empirical mixing model for particle exchange in the pulmonary region between the respiratory ducts and alveoli with parameters determined by fitting the model with recent measurements by Lin et al. The refined model was used to predict lobar, regional, and site -specific deposition of inhaled trace metals in the puff of regular and mentholated little cigars. Model refinements yielded increased deposition throughout the lung and matched deposition predictions more closely with measurements. The refined deposition model can be used to study the risk from inhalation of tobacco products as well as environment particles.