Convective Dispersion of an Aerosol Bolus in the Alveolar Region: A Numerical Approach

Abstract

This study presents a method for quantification of convective transport of a bolus (particle cloud) in the alveolar region. A computational fluid dynamics calculation was performed using a model of a single alveolus connected to a bronchiole. Moving wall boundary conditions and oscillating flow rates in the bronchiole were imposed to mimic breathing conditions. A passive scalar representing the aerosol bolus, injected at the inlet of the bronchiole, is tracked in the course of breathing cycles. The amount of scalar penetrating in the alveolus characterizes convective dispersion of bolus in the acinar airways. The amount of scalar remaining in the alveolus after several breaths may be used to estimate the residence time of bolus in the alveolus. The ratio Q _A /Q _D (Q _A and Q _D are respectively the flow rates entering the alveolus and the bronchiole) appears a key parameter to describe the variation in bolus dispersion and the bolus residence time. The peak value of bolus dispersion is observed for Q _A /Q _D =2.5(10^− 3. Bolus residence time also depends on the flow ratio Q _A /Q _D . These results emphasize the influence of specific alveolar flow patterns on convective dispersion in the alveolar region of the aerosol bolus in the alveolar region of the lungs. Such a data could be integrated into the existing models of particle deposition in the human airways.