Obstructive sleep apnea (OSA) severity might be correlated to the flow characteristics of the upper airways. We aimed to investigate the severity of OSA based on 3D models constructed from CT scans coupled with computational fluid dynamics (CFD) simulations. The CT scans of seven adult patients diagnosed with OSA were used to reconstruct the 3D models of the upper airways and CFD modeling and analyses were performed. Results from the fluid simulations were compared with the apnea-hypopnea index. Here we show a correlation between a CFD-based parameter, the adjusted pressure coefficient (Cp*), and the respective apnea-hypopnea index (Pearson’s r = 0.91, p = 0.004), which suggests that the anatomical-based model coupled with CFD could provide functional and localized information for different regions of the upper airways.
The existence of obstructions such as tracheal stenosis has major impacts on respiratory functions. Therapeutic effectiveness of inhaled medications is influenced by tracheal stenosis, and particle transport and deposition pattern are modified. The majority of studies have focused on obstructions in branches of the airways, where the flow is diverted to the other branches to meet the needed oxygen intake. In this study we have investigated the effects of trachea with and without stenosis/obstruction on particle depositions and air flow in a human respiratory system. Patient specific CFD simulations were conducted; CT-scans of a patient with tracheal stenosis were used to create 3D models of bronchial tree up to 8 generations. The section of the stenosis was manually modified to create a healthy trachea. Comparisons between CFD simulations before and after intervention demonstrate the impact of the stenosis on flow characteristics and particles distribution. The numerical investigations were performed using the implicit Unsteady Reynolds-Averaged Navier-Stokes equation (U-RANS), using the commercially available software (STAR-CCM+) from CD-Adapco, along with K-ω; shear stress transport model. Two sets of CT-images of inhalation and exhalation were used for assigning Patient-specific boundary conditions at the outlets. Lagrangian Phase model was used to simulate particle transport and depositions of 10, 5 and 2.5 micron diameter particles. Results of the particle depositions for 10 micron particles highlight the difference in depositions and ultimately inhaled medications in patients with and without tracheal stenosis. Particle deposition for normal Tidal volume increased due to stenosis from 47% to 51% for 10 Micron particles and not a significant change for the 2.5 Micron particles (from 4.5% to 4.7%). Comparisons of pressure drop in each generation between patient with tracheal stenosis and the healthy lung showed significant increase in pressure drop after the stenosis, which were experienced in all generations downstream. Experimental validation of the CFD results were made with a model of healthy trachea up to 3rd generation, manufactured using Additive Layer Manufacturing (ALM) from CT-images and pressure results were compared with the corresponding CFD results. Good agreements were found.
The presence of obstructions such as tracheal stenosis has important effects on respiratory functions. Tracheal stenosis impacts the therapeutic efficacy of inhaled medications as a result of alterations in particle transport and deposition pattern. This study explores the effects of the presence and absence of stenosis/obstruction in the trachea on air flow characteristics and particle depositions. Computational fluid dynamics (CFD) simulations were performed on three-dimensional (3D) patient-specific models created from computed tomography (CT) images. The analyzed model was generated from a subject with tracheal stenosis and includes the airway tree up to eight generations. CT scans of expiratory and inspiratory phases were used for patient-specific boundary conditions. Pre- and post-intervention CFD simulations' comparison reveals the effect of the stenosis on the characteristics of air flow, transport, and depositions of particles with diameters of 1, 2.5, 4, 6, 8, and 10 μm. Results indicate that the existence of the stenosis inflicts a major pressure force on the flow of inhaled air, leading to an increased deposition of particles both above and below the stenosis. Comparisons of the decrease in pressure in each generation between pre- and post-tracheal stenosis intervention demonstrated a significant reduction in pressure following the stenosis, which was maintained in all downstream generations. Good agreements were found using experimental validation of CFD findings with a model of the control subject up to the third generation, constructed via additive layer manufacturing from CT images.
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