http://orcid.org/0000-0003-0918-7505
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Abstract
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.
Nomenclature
| Amin | = | minimum cross-sectional area |
| CD | = | drag coefficient |
| Cin | = | number of particles entering from the inlet of the airways |
| Cout | = | number of particles that escaped at the outlet |
| dij | = | rate of the deformation tensor |
| dp | = | particle diameter |
| da | = | particle aerodynamic diameter |
| FD | = | drag force |
| FS | = | Saffman’s lift force |
| IP | = | inertial parameter |
| k | = | turbulent kinetic energy |
| mp | = | particle mass |
| mpds | = | physiological dead space rate |
| Rep | = | particle Reynolds number |
| Q | = | inhalation flow rate |
| Qres | = | breathing airflow rate at the nostril or oral surface |
| Tave | = | ensemble averaged elapsed time of particles |
| up | = | particle velocity |
| U | = | inlet air velocity |
Greek symbols
| ε | = | dissipation rate |
| Δt | = | time step for particle tracking |
| λ | = | mean free path of the fluid |
| ν | = | kinematic viscosity |
| µ | = | dynamic viscosity |
| η | = | deposition fraction |
| ρ | = | fluid density |
| ρp | = | particle density |
| τ | = | particle relaxation time |
| τn | = | nominal time constant |
| τw | = | shear stress at the wall |
| σ | = | Standard deviation |
Disclosure statement
No potential conflict of interest was reported by the authors.