A multiple-path model of particle deposition in the rat lung

A multiple-path model of particle deposition in the entire rat lower respiratory tract was developed. Deposition in every branch of an asymmetric lung model was calculated using published analytic formulas for efficiencies of deposition by sedimentation, diffusion, and impaction. The conducting airway tree of the model included the entire set of airway measurements for the Long-Evans rat collected by Raabe et al. (1976). A model acinus defined by Yeh et al. (1979) was attached to each terminal bronchiole. Deposition was calculated for each acinus. Substantial variations in acinar deposition were predicted. These depended on inhaled particle size and tidal volume. The standard deviation in acinar dose was on the order of 0.2 times the average dose. Dose to some pulmonary acini was nearly twice the average acinar dose, suggesting that the geometry of the conducting airway tree of the rat lung may cause a fraction of pulmonary sites to sustain damage from inhaled particles at levels of exposure which cause no effect in the majority of the lung. The results represent a first step toward a complete model of inhaled particle deposition which assesses the effect of heterogeneity of lung structure on deposition at the level of individual airways.