RESUMEN
BACKGROUND: The need for a better understanding of pulmonary diseases has led to increased interest in the development of realistic computational models of the human lung. METHODS: To minimize computational cost, a reduced geometry model is used for a model lung airway geometry up to generation 16. Truncated airway branches require physiologically realistic boundary conditions to accurately represent the effect of the removed airway sections. A user-defined function has been developed, which applies velocities mapped from similar locations in fully resolved airway sections. The methodology can be applied in any general purpose computational fluid dynamics code, with the only limitation that the lung model must be symmetrical in each truncated branch. RESULTS: Unsteady simulations have been performed to verify the operation of the model. The test case simulates a spirometry because the lung is obliged to rapidly perform both inspiration and expiration. Once the simulation was completed, the obtained pressure in the lower level of the lung was used as a boundary condition. The output velocity, which is a numerical spirometry, was compared with the experimental spirometry for validation purposes. CONCLUSIONS: This model can be applied for a wide range of patient-specific resolution levels. If the upper airway generations have been constructed from a computed tomography scan, it would be possible to quickly obtain a complete reconstruction of the lung specific to a specific person, which would allow individualized therapies.
Asunto(s)
Simulación por Computador , Pulmón/anatomía & histología , Pulmón/fisiología , Humanos , Hidrodinámica , Pulmón/fisiopatología , Tomografía Computarizada por Rayos XRESUMEN
One of the key challenges for computational fluid dynamics (CFD) simulations of human lung airflow is the sheer size and complexity of the complete, multiscale geometry of the bronchopulmonary tree. Since 3-D CFD simulations of the full airway tree are currently intractable, researchers have proposed reduced geometry models in which multiple airway paths are truncated downstream of the first few generations. This paper investigates a recently proposed method for closing the CFD model by application of physiologically correct boundary conditions at truncated outlets. A realistic, reduced geometry model of the lung airway based on CT data has been constructed up to generation 18, including extrathoracic, bronchi, and bronchiole regions. Results indicate that the new method yields reasonable results for pressure drop through the airway, at a small fraction of the cost of fully resolved simulations.
Asunto(s)
Bronquios/anatomía & histología , Bronquios/fisiología , Modelos Biológicos , Mecánica Respiratoria/fisiología , Broncografía , Simulación por Computador , Humanos , Procesamiento de Imagen Asistido por Computador , Procesos Estocásticos , Tomografía Computarizada por Rayos X , Tráquea/fisiologíaRESUMEN
Computational fluid dynamics (CFD) has emerged as a useful tool for the prediction of airflow and particle transport within the human lung airway. Several published studies have demonstrated the use of Eulerian finite-volume CFD simulations coupled with Lagrangian particle tracking methods to determine local and regional particle deposition rates in small subsections of the bronchopulmonary tree. However, the simulation of particle transport and deposition in large-scale models encompassing more than a few generations is less common, due in part to the sheer size and complexity of the human lung airway. Highly resolved, fully coupled flowfield solution and particle tracking in the entire lung, for example, is currently an intractable problem and will remain so for the foreseeable future. This paper adopts a previously reported methodology for simulating large-scale regions of the lung airway (Walters, D. K., and Luke, W. H., 2010, "A Method for Three-Dimensional Navier-Stokes Simulations of Large-Scale Regions of the Human Lung Airway," ASME J. Fluids Eng., 132(5), p. 051101), which was shown to produce results similar to fully resolved geometries using approximate, reduced geometry models. The methodology is extended here to particle transport and deposition simulations. Lagrangian particle tracking simulations are performed in combination with Eulerian simulations of the airflow in an idealized representation of the human lung airway tree. Results using the reduced models are compared with those using the fully resolved models for an eight-generation region of the conducting zone. The agreement between fully resolved and reduced geometry simulations indicates that the new method can provide an accurate alternative for large-scale CFD simulations while potentially reducing the computational cost of these simulations by several orders of magnitude.
Asunto(s)
Pulmón/fisiología , Modelos Biológicos , Ingeniería Biomédica , Simulación por Computador , Humanos , Hidrodinámica , Pulmón/anatomía & histología , Modelos Anatómicos , Tamaño de la Partícula , Mecánica Respiratoria/fisiología , Procesos EstocásticosRESUMEN
The DigitalLung project represents an attempt to develop a multi-scale capability for simulating human respiration with application to predicting the effects of inhaled particulate matter. To accomplish this objective, DigitalLung integrates macroscale models of integrative human physiology, meso-to-microscale computational fluid dynamics simulations of a breathing human lung, meso-to-nanoscale particle transport and deposition models, and micro-to-nanoscale physical and chemical characterizations of particulate and their mass transfer through the mucosal layer to the epithelium. This chapter describes preliminary results and areas of ongoing research.