The effect of heterogeneity of lung structure on particle deposition in the rat lung

Differences in particle deposition patterns between human and rat lungs may be attributed primarily to their differences in breathing patterns and air way morphology. Heterogeneity of lung structure is expected to impact acina r particle deposition in the rat. Two different morphometric models of the rat lung were used to compute particle deposition in the acinar airways: th e multiple-path lung (MPL) model (Anjilvel and Asgharian, 1995, Fundam, App l. Toxicol. 28, 41-50) with a fixed airway geometry, and the stochastic lun g (SL) model (Koblinger and Hofmann, 1988, Anat. Rec. 221, 533-539) with a randomly selected branching structure. In the MPL model, identical acini wi th a symmetric subtree (Yeh et al., 1979, Anat. Rec. 195, 483-492) were att ached to each terminal bronchiole, while the respiratory airways in the SL model are represented by an asymmetric stochastic subtree derived from morp hometric data on the Sprague-Dawley rat (Koblinger ef nl., 1995, J, Aerosol . Med. 8, 7-19). In addition to the original MPL and SL models, a hybrid lu ng model was also used, based on the MPL bronchial tree and the SL acinar s tructure. Total and regional deposition was calculated for a wide range of particle sizes under quiet and heavy breathing conditions. While mean total bronchial and acinar deposition fractions were similar for the three model s, the SL and hybrid models predicted a substantial variation in particle d eposition among different acini. The variances of acinar deposition in the MPL model were consistently much smaller than those for the SL and the hybr id lung model. The similarity of acinar deposition variations in the two la tter models and their independence on the breathing pattern suggests that t he heterogeneity of the acinar airway structure is primarily responsible fo r the heterogeneity of acinar particle deposition.