Air Distribution And Flow In The Bronchial Tree Of Human Lungs

Respiratory diseases have become very common ailments threatening people's health and lives with environmental deteriorating. Many factors, such as atmospheric pollution, water pollution, food pollution, population density leaping and high-pressured life style, etc. could be counted as the causes. Currently, variety of researches in biological and medical fields is being carried out. For instance, investigations into the changes of molecular biology in pathological changes of the lungs from the angle of oxygen-derived free radicals and DNA, the observation of micro- configuration using various microscopes, investigation of the apparent characteristics of diseases through animal test and clinic diagnosis, etc. have proved helpful approaches. Although more and more newly-developed techniques and equipment mentioned above have come into use in clinic diagnosis and therapies, many problems are kept unsolved in the research of the lungs. Pressure distribution and airflow status in the bronchial tree cannot be measured directly and exactly due to the complex and fragile structure of the bronchial tree, with only the pressure in the trachea and lungs being measured indirectly in other ways. This is an obstacle to the diagnosis and cure of the lung diseases. So physical and mechanical modeling is but a feasible method to explore the airflow and pressure distribution in bronchial tree during respiration.Many a mathematical model about investigation into airflow in the trachea, gas exchange in the lungs, pressure drop in the bronchial passages, and lung ventilationhave been set up and some useful results have been obtained. However, in view of the resistance of pulmonary ventilation, these mathematical models simplified respiratory system into several parts in order to make a overall study, so that they are lack of considering localities of the bronchial tree and do not give the differences of airflow between various locations.The air distribution and airflow status in the bronchial tree has been dealt with in the present thesis in two different ways - local and overall. Based on the theory of fluid network, a three-element lumped parameter model of bronchial tree was proposed in the overall treatment. It was assumed that the upper five or seven generations of the twenty-four generations of the respiratory airway are asymmetric, while the rest are symmetric. The Gear method was applied to solve the ordinary differential equations of the mathematical model. The pressure and flow rate distributions in different positions of the lungs have been computed, and fairly reasonable pressure change and air distribution along the upper generations of bronchial tree have been obtained. In addition, the effects of partial bronchial obstruction on the change of pressure and flow at different locations in the bronchial tree were compared to the results under the normal physiological conditions. Based on the basic theory and software of computational fluid mechanics, two dimensional and three dimensional flows at the bifurcation area of the first generation were modeled and solved mathematically in the local treatment. The results of the change of flow during a single respiratory period were matched with the observance of experiment by other authors. The results were also compared to those in steady conditions.The results of this research may lead to meaningful understanding of the distribution of airflow along the bronchial tree under physiological and pathological conditions and may offer a helpful basis for the further study in the theoretical and clinical research of the resistance and the airflow along normal and blocked respiratory airways.