Micrometer aerosol deposition in normal and emphysematous subacinar models

Emphysema is a chronic respiratory disease characterized by interalveolar septa destruction and enlarged air sacs. How the inhalation dosimetry in the pulmonary acini varies in the time course of emphysema is still unclear. The aim of this study is to numerically evaluate the impact of septal destructions on particle deposition in a pyramid-shape subacinar model that is composed of 496 alveoli. Four emphysematous models were generated by progressively removing the inter-alveolar septa from the normal geometry. Spatial distribution and temporal evolution of particle deposition were quantified in expanding/contracting subacinar models on both total and regional basis using a well-validated discrete-phase Lagrangian model. Airflow fields in the subacinar cavities are sensitive to the septal raptures, with regular, radial streamlines in the proximal alveoli in the normal geometry in contrast to unsymmetrical and recirculating flows in the emphysematous subacini. Intensified collateral ventilation and significantly increased doses in the outer wall and base are observed in disease than heath. The deposition rate of small particles (1-1.5 μm) is more sensitive to the level of septal rapture than large particles (2.5-3 μm). Unexpectedly, more particles per unit area deposit on the outer wall and at the base of the subacinus than on the inner septal walls. The subacinus-averaged doses increase with progressing septal destructions, suggesting an escalating risk factor to the acinar health at the late stages of emphysema.