The macrotransport properties of aerosol particles in the human oral-pharyngeal region

A method is described for evaluating the mean velocity, dispersion coefficient and deposition rate constant characterizing aerosol transport in a finite, computationally tractable, three-dimensional domain of the human lungs. The methodology is applied specifically to deduce (mesoscale) transport coefficients in an anatomically realistic human mouth and throat. In this method aerosol particles are introduced into a numerically simulated airflow in the vicinity of the entrance region of the airway unit (e.g. the mouth); the aerosol bolus is inspired such that it travels through the airway unit before being expired. The exhaled concentration of nondeposited aerosols is determined numerically, and used to deduce the three aerosol transport coefficients. The deduced transport coefficients, representing “mesoscale” averages of the microscale simulated flow, are determined as functions of air flow rate, particle size, bolus parameters, and dimensionality; these values are then incorporated into a mesoscale lung model and used to simulate macroscale aerosol transport behavior in the lungs. Special attention is given to the numerical simulation of an aerosol bolus inspired into the lungs. The calculated half-width, mode and deposition fraction agree favorably with recent macrotransport simulations, minus the upper airway generation. In these comparisons, the major influence of the upper airways is to increase aerosol deposition. Half-width and deposition fraction are also significantly affected by lung size.