10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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A Multiscale Model for Evolving Multispecies Aerosol Deposition and Absorption in the Human Lung
Ravi Kannan, Z.J. Chen, ANDRZEJ PRZEKWAS, Florian Martin, Julia Hoeng, Arkadiusz Kuczaj, CFD Research Corporation
Abstract Number: 992 Working Group: Aerosol Modeling
Abstract Computational fluid dynamics (CFD) models able to predict aerosol transport, evolution and deposition are useful in supporting and predicting in vitro and in vivo aerosol exposure and dosimetry results. Their ultimate goal of development and application would be to become integrated with in vitro bio-fluidics and in vivo physiological responses of the studied systems (e.g., CFD-PBPK linked approaches). The required level of sophistication of such mathematical models depends on the specific application. It is also often limited by the computational complexity of the respiratory system anatomy, and physiology. Detailed CFD aerosol deposition models are typically used for the trachea and upper bronchi, due to their high computational complexity and cost, while the approximate whole-lung models, such as the Typical Path Lung model, have issues concerning their application and accuracy.
To overcome the above mentioned barriers we have developed a novel multiscale computational model of human lung respiration physiology, including the inhalation of aerosols and their deposition on the airway walls followed by absorption and clearance via mucosal and alveolar barriers. In the conventional aerosol inhalation simulations, the airways are generally split into the upper airways and alveolar sections. Such “compartmental” models result in low-resolution results and the spatial resolution of the deposited aerosol cannot be accurately calculated. The foundation of the present multiscale model is the high-resolution anatomical geometry of a human entire respiratory tract from the mouth to the alveolar zone.
A two-step computational algorithm is used to predict the aerosol deposition. In the first step, high-fidelity 3D CFD simulations, on the adaptive Cartesian mesh, are performed to simulate air flows and transport of aerosol and gaseous compounds of the aerosol mixture. The spatial lung airway wall deposition patterns are computed and stored. In the second step, a novel, computationally efficient Quasi-3D (Q3D) airway wall barrier model is used to simplify the geometry and simulate both mucociliary and trans-mucosal absorption of the deposited compounds. The Q3D method preserves the 3D geometrical structure, delivering extremely accurate solutions and being approximately 25000 times faster than CFD methods. The Q3D lung airway model is then populated to around 15 generations (tracheo-bronchial limit). The alveolar region can be modeled using simplified bolus-type sacs matching the alveolar surface area, at the end of each bronchial leaf.
In the present multiscale model, the 3D CFD method is used to simulate the aerosol transport/deposition up to the first three airway generations. The Q3D model is then used to simulate aerosol transport/deposition in the distal airways. The resulting deposition is then used as the airway barrier model to simulate deposited aerosol mucociliary clearance and trans-mucosal absorption. The resulting mucociliary model is first implemented and validated against the experimental clearance results, involving non-absorbing radiolabeled particles. The paper presents selected validation results for the aerosol transport, deposition, and clearance in the lungs and comparison between previously published models and available experimental data.