Deposition of bronchiole-originated droplets in the lower airways during exhalation

Abstract

Recent studies have shown that small expired droplets that contain pathogens may play a significant role in the transmission of respiratory diseases. However, there is little data on the generation of droplets from the bronchioles and their deposition in the lower airways during exhalation. We apply a computational fluid dynamics method to study expiratory air flow in a truncated model of the adult lower airways. Assumptions are made to evaluate the transport and deposition of droplets along the airway as these droplets are released in various regions in the conducting airways during exhalation. We find that large droplets (i.e., >5 μm) generated from the bronchioles are very likely to be blocked by the lower airways, whereas those in the submicron range (i.e., <1 μm) easily survive the conducting tracts and are likely to be exhaled. The locations at which large droplets from the bronchioles are deposited are limited to the terminal regions, which means that these droplets are unlikely to be released again via possible aerosolization due to the shear force on the airway walls. The evidence from the computational fluid dynamics simulation suggests that particle size plays an important role in virus transmission and disease diagnosis.