Numerical Modeling of Forced Expiratory Flow in a Human Lung

During a forced expiratory maneuver, the lung experiences large volume excursions accompanied by large changes in geometry. This test of pulmonary function can be effectively used to diagnose and assess the severity of different lung diseases and has been used extensively in clinical medicine. Due to the complexity of the associated fluid dynamics, a comprehensive appreciation of the relationship between altered flowvolume curves and the underlying pathology still escapes our grasp even though many characteristics of the lung behavior have been examined. In this thesis, a numerical model is developed, which extends previous models by incorporating unsteady inertia, branching asymmetry, and an "effective" airway liquid layer. The resulting model is capable of calculating flow conditions from the alveolar zone to the airway opening in a single calculation. The results indicate significant improvements over previous models in predicting the clinically-observed flow-volume curve, especially near low lung volume. The model's ability to deal with intrinsically unsteady flow led to the exa.mination of other maneuvers such as cough, forced oscillation, and high frequency ventilation. The results elucidate the key features of these unsteady phenomena and show good agreement with the experimental findings. The current model can now be used as a foundation for more extensive studies. Thesis Supervisor: Roger D. Kamm Title: Professor of Mechanical Engineering Numerical Modeling of Forced Expiratory Flow in a Human Lung by James Jang-Sik Shin Submitted to the Department of Aeronautics and Astronautics on January 30, 1992, in partial fulfillment of the requirements for the degree of Master of Science in Aeronautics and Astronautics Abstract During a forced expiratory maneuver, the lung experiences large volume excursions accompanied by large changes in geometry. This test of pulmonary function can be effectively used to diagnose and assess the severity of different lung diseases and has been used extensively in clinical medicine. Due to the complexity of the associated fluid dynamics, a comprehensive appreciation of the relationship between altered flowvolume curves and the underlying pathology still escapes our grasp even though many characteristics of the lung behavior have been examined. In this thesis, a numerical model is developed, which extends previous models by incorporating unsteady inertia, branching asymmetry, and an "effective" airway liquid layer. The resulting model is capable of calculating flow conditions from the alveola.r zone to the airway opening in a single calculation. The results indicate significant improvements over previous models in predicting the clinically-observed flow-volume curve, especially near low lung volume. The model's ability to deal with intrinsically unsteady flow led to the examination of other maneuvers such as cough, forced oscillation, and high frequency ventilation. The results elucidate the key features of these unsteady phenomena and show good agreement with the experimental findings. The current model can now be used as a foundation for more extensive studies.During a forced expiratory maneuver, the lung experiences large volume excursions accompanied by large changes in geometry. This test of pulmonary function can be effectively used to diagnose and assess the severity of different lung diseases and has been used extensively in clinical medicine. Due to the complexity of the associated fluid dynamics, a comprehensive appreciation of the relationship between altered flowvolume curves and the underlying pathology still escapes our grasp even though many characteristics of the lung behavior have been examined. In this thesis, a numerical model is developed, which extends previous models by incorporating unsteady inertia, branching asymmetry, and an "effective" airway liquid layer. The resulting model is capable of calculating flow conditions from the alveola.r zone to the airway opening in a single calculation. The results indicate significant improvements over previous models in predicting the clinically-observed flow-volume curve, especially near low lung volume. The model's ability to deal with intrinsically unsteady flow led to the examination of other maneuvers such as cough, forced oscillation, and high frequency ventilation. The results elucidate the key features of these unsteady phenomena and show good agreement with the experimental findings. The current model can now be used as a foundation for more extensive studies. Thesis Supervisor: Roger D. Kamm Title: Professor of Mechanical Engineering