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The biomechanical behaviors of respiratory system in terms of alveolar pressure variation, local ventilation capacity, etc., are very important in the diagnosis and treatment of lung diseases. However, such local information cannot be directly obtained by the conventional clinical examination methods. A biomechanical simulation method for the whole respiratory system is required to reveal the detailed biomechanical state during various situations. In this study, we have developed a simulation method that is able to reproduce the biomechanical behaviors of lung deformation, thoracic movement due to contraction and relaxation of the intercostal muscles, multi-scale airflows in the bronchi, etc. Our developed simulation system includes a mesh model of respiration system including rib, vertebral bones, intercostal muscle, diaphragm, heart and lung and bronchus. In order to reproduce the contraction of the intercostal muscles and the diaphragm, we adopted a muscle constitutional model with the consideration of the muscle fiber direction. A multiscale method is proposed for simulating the pulmonary airflow. Airflow in the respiratory bronchioles and alveoli were calculated by a two-phase mixture model (0D) coupled with the lung deformation. The terminal bronchioles were approximated by a pipe model (1D) which is connected with the 0D lung parenchyma. For the airflow inside the trachea and bronchus, a three dimensional (3D) computational fluid dynamics analysis was performed using the real bronchial geometry extracted from CT images (3D). The multi-scale respiratory simulation system was realized by satisfying the mass and momentum conservation law. In addition, the continuous condition of pressure was also ensured at the terminal nodes of the 1D airways and the corresponding mesh central points of 0D mixture solid. The coupling between 3D bronchus and 1D terminal bronchioles is conducted by transferring the information of the flow rate and pressure between the 3D bronchial terminal’s outlets and the connected 1D bronchioles inlets. Finally, the biomechanical simulation of inhalation process was performed by lung volume expansion owing to the contraction of intercostal muscles and diaphragm based on the physiological phenomena.The developed numerical respiratory system has great potential for not only providing useful information in terms of predicting biomechanical behaviors of lung tissues, but also estimating the respiratory function. Moreover, the detailed distribution of vital capacity, stress of lung and airflow’s velocity can be obtained numerically, which are helpful for more effective treatment planning.

Multiscale modeling; pulmonary airflow simulation; respiratory system