The effect of alveolar mixing on particle retention and deposition investigated by a dynamic single-path model

Abstract

A dynamic, single-path model is developed for dry powder transport in the lungs. The model differentiates between particle behavior in the respiratory bronchioles and alveolar ducts on one hand and inside the alveoli on the other. In particular, it considers the alveolar volume of each generation as a mixing chamber. Air inflow to the alveoli is calculated by accounting for the deformation of airways during breathing. Particle dispersion along the respiratory tract is taken into account and mechanistic deposition rates are developed for the alveoli. Deposition by Brownian diffusion is modeled by a concentration boundary layer, whose thickness varies inversely with the intensity of mixing. The plausibility of the assumption of alveolar mixing is tested indirectly by comparison of model predictions with benchmark data of the exhaled concentration profile and of the pulmonary deposition of continuously inhaled aerosols. The observed agreement lends support to the hypothesis that alveolar mixing represents fundamental physics of the breathing process. It also supports the suggestion that alveolar mixing provides an additional axial dispersion mechanism in the acinus, which is independent of particle size and is active at zero gravity. Copyright © 2020 American Association for Aerosol Research. © 2020, © 2020 American Association for Aerosol Research.