Modelling inhaled particle deposition in the human lung—A review

Comparison of micro- and nano-size particle depositions in a human upper airway model

Computational fluid dynamics (CFD) simulations of airflow and particle deposition in geometries representing the human tracheobronchial tree were conducted. Two geometries were used in this work: (1) based on the Weibel A model, and (2) based on a CT scan of a cadaver lung cast. Flow conditions used included both steady-state inhalation and exhalation conditions as well as time-dependent breathing cycles. Particle trajectories were calculated in each of these models by solving the equations of motion of the particle for the deterministic portion of particle displacement, and adding a stochastic Brownian term at each step. The trapping of particles on the wall surfaces was monitored, and the locations of trapping in each generation were recorded. The results indicate that there are dramatic differences in the predicted deposition between the two models. The intragenerational deposition locations show that in regions where the deposition mechanism is inertial impaction, the predominant deposition seems to be at the airway bifurcations. The results of this study suggest that under most conditions, an idealized model based on the Weibel dimensions is not sufficient to predict deposition, and an accurate model, such as those based on imaging techniques may be required.

Computational fluid dynamics simulation of airflow and aerosol deposition in human lungs.

Characteristics of the turbulent laryngeal jet and its effect on airflow in the human intra-thoracic airways

Airflows in the nasal cavities and oral airways are rather complex, possibly featuring a transition to turbulent jet-like flow, recirculating flow, Dean's flow, vortical flows, large pressure drops, prevailing secondary flows, and merging streams in the case of exhalation. Such complex flows propagate subsequently into the tracheobronchial airways. The underlying assumptions for particle transport and deposition are that the aerosols are spherical, noninteracting, and monodisperse and deposit upon contact with the airway surface. Such dilute particle suspensions are typically modeled with the Euler-Lagrange approach for micron particles and in the Euler-Euler framework for nanoparticles. Micron particles deposit nonuniformly with very high concentrations at some local sites (e.g., carinal ridges of large bronchial airways). In contrast, nanomaterial almost coats the airway surfaces, which has implications of detrimental health effects in the case of inhaled toxic nanoparticles. Geometric airway features, ...

Airflow and Particle Transport in the Human Respiratory System

Considering oscillatory laminar incompressible three-dimensional flow in triple planar and nonplanar bifurcations representing generations three to six of the human respiratory system, air flow fields and micron-particle transport have been simulated under normal breathing and high-frequency ventilation (HFV) conditions. A finite-volume code (CFX4.3 from AEA Technology, Pittsburgh, PA) and its user-enhanced FORTRAN programs were validated with experimental velocity data points for a single bifurcation. The airflow structures and micron-particle motion in the triple bifurcations were analyzed for a representative normal breathing cycle as well as HFV condition. While both the peak inspiratory and expiratory velocity profiles for the low Womersley case (α=0.93) agree well with those of instantaneously equivalent steady-state cases, some differences can be observed between flow acceleration and deceleration at off-peak periods or near flow reversal, especially during inspiratory flow. Similarly, the basic features of instantaneous particle motion closely resemble the steady-state case at equivalent inlet Reynolds numbers. The preferential concentration of particles caused by the coherent vortical structures was found in both inhalation and exhalation; however, it is more complicated during expiration. The effects of Womersley number and non-planar geometries as well as the variations in secondary flow intensity plus pressure drops across various bifurcations under normal breathing and HFV conditions were analyzed as well. This work may elucidate basic physical insight of aerosol transport relevant in dosimetry-and-health-effect studies as well as for drug aerosol delivery analyses.

Z. Zhang

Papers

Transient airflow structures and particle transport in a sequentially branching lung airway model