Modeling particle transport and deposition in the human lung

Extensive efforts have been made to model particle deposition in the human lung based on a single breath. However, accurate estimates of regional particulate dosimetry for long-term PM exposures cannot be obtained without considering transport and deposition of the retained particles over successive breathing cycles.;The specific aim of this dissertation is to develop a particle deposition model for the entire lung during multiple breathing cycles. To accomplish this, a single breath model that describes aerosol bolus dispersion and deposition for the entire lung has to first be developed. The model assumes that particle transport on inhalation and exhalation differs due to secondary flow asymmetries at the bifurcations. This single breath model provides a framework for the simulation of particle transport during multiple breaths. By simulating multiple breath transport and deposition of 0.5 mum particles, which have a significant fraction that remains suspended at the end of the breathing cycle, we find that the retained particle concentration increases with each tidal cycle and these particles penetrate deeper with succeeding breaths. Predicted 0.5 mum particle deposition fraction per generation during steady-state breathing showed similar patterns to other single breath model simulations yet predicted higher deposition fractions in the more proximal pulmonary regions. The total and regional dosimetry of particles in different sizes (0.01 ∼ 10 mum) was estimated after the lung attains a steady state during multiple breathing cycles. Although fine-mode particles (0.01 ∼ 10 mum) have the lowest overall deposition rate in the pulmonary regions, the retained fractions at the end of exhalation are significantly higher (14 ∼ 32%) than the ones during a single breath. Therefore, these retained fractions have to be considered for the estimation of particle dosimetry in humans to evaluate long-term PM exposure.;Although the models developed in this study are not intended to simulate detailed flow mechanics in the lung, they simulate the observed aerosol bolus dispersion and deposition by employing overall particle transport mechanisms during multiple breaths. Hence these models can be powerful tools to explain pulmonary particle deposition associated with longer term PM exposures.