The Numerical Simulation Research On Inhaled Particle Deposition And Impact Of Obstruction In Pulmonary Acinus

In recent years, with the development of economy and increasing of environment pollution, the morbidity and mortality of respiratory diseases are increasing rapidly. After being breathed in, inhalable particles, especially PM2.5 can flow into respiratory system and deposit in pulmonary acinus, even penetrate into blood circulation system, cause harm to the health of human. Children is more inhalable particles, since whose respiratory system is still growing and immunity is low. Therefore, analyzing the characteristics of airflow and particle deposition in adults and children pulmonary acinar is important for understanding the transport mechanism and evaluating the impact on different age groups, and will contribute to the intensive study in related fields. Research on the deposition of drug particles in pulmonary alveolar, can be used to evaluate drug targeting and provide solid theoretical basis for further improvement and optimization of targeted drug therapy.At present, there are only histological slices graphics, since the real physiological structure of the pulmonary acinus with small scale, large number of alveoli and the complicated structure. Experiments at large scale, which based on principle of similarity, are often done to observe the patterns of fluid flow and particle deposition. In contrast, numerical simulation that is not restricted by methods, can show the flow details. We establish the whole pulmonary acinus 3D healthy and 2D obstructive model of 0~8 generations based on Weibel-A model, and the dynamic mechanism of rhythmic contraction/expansion through the moving wall boundary condition is applied to simulate airflow and particle deposition patterns both in adults and children pulmonary acinar, impact from obstructive pulmonary acinus and targeting of drug particle. We use the multiphysics numerical simulation software COMSOL Multiphysics 4.3a to simulate, and Euler and Lagrange methods are chosed to simulate the airflow pattern and particle deposition respectively.Research on healthy pulmonary acinus shows that with the increasing of generations, velocity decreases, while pressure value and deposition efficiency of each generation increase. Deposition efficiency in 3D model is higher than that in 2D model, and 3D structure cannot be ignored in research on pulmonary acinus flow characteristics. Convective flow is enhanced under moving wall boundary condition, leading to higher deposition efficiency than that under stationary wall boundary condition. Deposition efficiency differs under different breathing condition, mainly due to the effect of breathing time. Moreover, by comparing the simulation results of adults and children, we find that the younger, the greater of airflow velocity, pressure value, and deposition efficiency.Research on obstructive pulmonary acinus shows that the flow rate at the upstream, downstream and symmetrical tube of obstructive generation are all affected by obstruction. Pressure drop near the obstruction is larger than that at any sites else, which increases with increasing of distance to distal pulmonary acinus. Obstruction has almost no impact on the tube symmetrically and has mainly impact on the downstream divider. In general, it is unlikely to choose the best targeting drug size, drug targeting is related to several complex factors such as obstruction sites and number of obstructions.