Three Dimensional Modelling Of Lung Airway Tree And Research Of Airflow In It

Lung airway tree is the gas transport channels between pulmonary capillary vessel and atmosphere. It has great influence on airflow and on its physiological function. Clinical medicine has indicated that respiratory disease symptoms always occur at the bifurcated segments. Understanding the mechanism of bifurcate airflow is of great significance to the analysis of the mechanism of the diseases in the respiratory airway, control and optimization of diffusion and deposition of powder or mist medicine in the conducting airways.Historically, airflow in the respiratory airways has been investigated by a great number of respiratory researchers and doctors. However, their works were fundamentally based on Weibel's symmetric model, and no more than two respiratory airway generations were dealt with. In a word, they did not pay attention to the asymmetrical characteristics of the human lung airway tree.A three-dimensional model was developed in this thesis, in which the lung airway tree's characteristics can be described better. Based on anatomical data from the literature and the principle of lowest energy consumption, a three-dimensional fractal model of the conducting airways was set up using a volume-splitting algorithm. Specific data of the lengths at various grades, branching angles, and capillary diameters were calculated. As a result, the computed data were identical with those of the existing statistical data. Polyhedron with six squares and eight hexagonal faces was used as the basic structure of alveolus using fractal geometrical theory. By combination of 14-face polyhedron, the elementary structural unit with first stage and second stage was established. By introducing the random parameters to the graphic construction process, and a series of mathematical transformation, aprimary graph of "acinus" and "alveoli" was obtained. After further affine transformation, blur operation of border line and passive calculation of the angles of the "alveoli", the authors obtained a satisfactory graph of acinus and alveoli which was similar to those in a real alveolar photo. The computed result indicates that complicated natural objects could be imaged by mathematical methods.With the generated asymmetric three-dimensional mathematical model, we used the graphic tool "Gambit" to establish the asymmetric lung airway tree, we performed the numerical simulation of respiratory flow in the conducting airways (from trachea to the third grade) by using Fluent software. We analyzed the velocity distribution of airflow throughout the bronchial tree under different bifurcation patterns and orders, physiological and pathological condition. The influence of bifurcation pattern and grid size on the calculated results was discussed. The unsteady flow during one respiratory period was calculated, the effects of three-grad and four-grad bifurcation to airflow discussed. At last the flow distribution under physiological, pathological, and different breathing conditions were computed.The three-dimensional algorithm proposed in this thesis provides an effective approach for generating conducting airway models. The result of numerical simulation may lead to meaningful understanding of the distribution of airflow along the bronchial and may set up a helpful basis for further study in theoretical and clinical research of the respiratory airways.