Regional deposition of inhaled aerosols is essential for assessing health risks from toxic exposure. Upper airway physiology plays a significant role in respiratory defense by filtering micrometer particles, whose deposition mechanism is predominantly inertial impaction and is mainly controlled by airflow characteristics. The monkey is commonly used in tests that study inhalation toxicity as well as in preclinical tests as human surrogates due to their anatomical similarities to humans. Therefore, accurate predictions and an understanding of the inhaled particles and their distribution in monkeys are essential for extrapolating laboratory animal data to humans. The study goals were as follows: (1) to predict the particle deposition based on aerodynamic diameters (1–10 µm) and various steady inspiratory flow rates in computational models of monkey and human upper airways; and (2) to investigate potential differences in inhalation flow and particle deposition between humans and monkeys by comparing numerical simulation results with similar in-vitro and in-vivo measurements from recent literature. The deposition fractions of the monkey’s numerical airway model agreed well with in-vitro and human model data when equivalent Stokes numbers were compared, based on the minimum cross-sectional area as representative of length scale. Vestibule removal efficiencies were predicted to be higher in the monkey model compared with the human model. Our results revealed that the particle transportations were sensitive to the anatomical structure, airway geometry, airflow rates, inflow boundary conditions and particle size.

Infectious respiratory diseases have long been a serious public health issue, with airborne transmission via close person-to-person contact being the main infection route. Coughing episodes are an eruptive source of virus-laden droplets that increase the infection risk of susceptible individuals. In this study, the droplet generation process during a coughing event was reproduced using the Eulerian wall film (EWF) model, and the absorption/expulsion of droplets was tracked using the discrete phase model (DPM). A realistic numerical model that included the oral cavity with teeth features and the respiratory system from the throat to the first bifurcation was developed. A coughing flow profile simulated the flow patterns of a single coughing episode. The EWF and DPM models were coupled to predict the droplet formation, generation, absorption, and exhalation processes. The results showed that a large droplet number concentration was generated at the beginning of the coughing event, with the peak concentration coinciding with the peak cough rate. Analysis of the droplet site of origin showed that large amounts of droplets were generated in the oral cavity and teeth surface, followed by the caudal region of the respiratory system. The size of the expelled droplets was 0.25–24 μm, with the peak concentration at 4–8 μm. This study significantly contributes to the realm on the site of origin and localized number concentration of droplets after a coughing episode. It can facilitate studies on infection risk assessment, droplet dispersion, and droplet generation mechanisms from other sneezing or phonation activities.

One of the most promising approaches to understand inhalation toxicology and to assess the potential risks of inhaled particles is to examine the disposition of the hazardous airborne particles in ...