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Fate of Inhaled Biological-agent Containing Aerosol Droplets in the Human Respiratory Tract
BAHMAN ASGHARIAN, Owen Price, Jennifer Chesnutt, Gene McClellan, Jason Rodriguez, Applied Research Associates, Inc.
Abstract Number: 82
Working Group: Health-Related Aerosols
Abstract
Aerosolized biological agents originating in a liquid suspension potentially have hygroscopic properties. These hygroscopic aerosols undergo phase change during which the size (and mass) of an aerosol changes depending on the relative humidity of the environment in which the aerosols are suspended. When the size of an aerosol changes, so do its deposition characteristics in the respiratory tract. To assess the fate of inhaled biological agents in the respiratory tract, size change during transport and deposition in the entire respiratory tract were modeled during inhalation, pause, and exhalation. Existing models for insoluble, non-hygroscopic aerosols were modified and extended to account for the influence of size change on deposition in lung airways. The behavior of agent containing droplets depended additionally on the temperatures of the droplet and air as well as the relative humidity of the air in the entire respiratory tract. Thus, a comprehensive model for aerosol size change and deposition was developed to predict aerosol deposition for agent exposure health risk. Major mechanisms of deposition were inertial impaction, Brownian diffusion, and gravitational settling. Droplets continued to grow in the respiratory tract. As a result, deposition characteristics of hygroscopic droplets were different from those of insoluble particles. When compared to insoluble particles, deposition fractions of hygroscopic droplets in the respiratory tract were found to decrease for initial sub-micrometer aerosols and increase for fine and coarse droplets. This study aids in developing an exposure-dose-response model for inhaled biological agents. This study was funded by Defense Threat Reduction Agency, contract HDTRA1119C0022.