Numerical and experimental studies of air and particle flow in the realistic human upper airway models

摘要

The human upper airway structure provides access of ambient air to the lower respiratory tract, and it as an efficient filter to cleanse inspired air of dust bacteria, and other environmental pollutants. When air passes through airway passages, it constantly changes direction, which may lead to flow separation, recirculation, secondary flow and shear stress variations along the airway surface. Therefore, it is essential to understanding the air transport processes within the upper airway system. The functions are respiratory defence mechanisms that protecting the delicate tissues of the lower airway from the often harsh conditions of the ambient air. While protecting the lower respiratory system, however, the upper airway itself becomes susceptible to various lesions and infections from filtration of environmental pollutants. Inhaled particle pollutants have been implicated as a potential cause of respiratory diseases. In contrast, inhalation of drug particles deposited directly to the lung periphery results in rapid absorption across bronchopulmonary mucosal membranes and reduction of the adverse reactions in the therapy of asthma and other respiratory disorders. For this purpose, it is desirable that the particles should not deposit in the upper airways before reaching the lung periphery. Therefore, accurate prediction of local and regional pattern of inhaled particle deposition in the human upper airway should provide useful information to clinical researchers in assessing the pathogenic potential and possibly lead to innovation in inhalation therapies. With the development of the increasing computer power and advancement of modeling software, computational fluid dynamics (CFD) technique to study dilute gas-particle flow problems is gradually becoming an attractive investigative tool. This research will provide a more complete picture of the detailed physical processes within the human upper airway system. Owing to the significant advancements in computer technologies, it will allow us to efficiently construct a full-scaled model integrating the various functional biological elements including the nasal, oral, laryngeal and more generations of the bifurcation of the human upper airway system through imagining methodologies. A significant advantage of this human model is that the differences in airway morphology and ventilation parameters that exist between healthy and diseased airways, and other factors, can be accommodated. This model will provide extensive experimental and numerical studies to probe significant insights to the particle deposition characte ristics within the complex airway passages and better understanding of any important phenomena associated with the fluid-particle flow. It will also lead to an improved understanding of fluid/particle transport under realistic physiological conditions. New concepts and numerical models to capture the main features observed in the experimental program and innovative techniques will be formulated. The ability to numerically model and a better physical understanding of the complex phenomena associated with the fluid dynamics and biological processes will be one of the major medical contributions especially targeting drug delivery and health risk analysis. Its biomedical engineering significance lies in the fact that this will enable us to accurately evaluate potential biological effects by the inhaled drug particles, facilitating new drug research and development.