Auflistung nach Autor:in "Gurumurthy, Pragathi"

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Experimental investigation and validation of CFD simulations of steady flow in stenosis and pharynx using 2D PC-MRI and 4D flow MRI
(2025) Gurumurthy, Pragathi
Obstructive sleep apnea (OSA) is a sleep disorder of repetitive disrupted breathing caused by partial or complete closure of the upper airway, despite the effort to breathe. The sleep disorder not only causes social impact on the patient such as daytime sleepiness, fatigue but it has also been linked to several heart conditions. A combination of anatomical variations, impaired neuromuscular functions, ventilatory instability and premature awakening cause OSA. Due to the complex and heterogeneous nature of the disease, the etiology of OSA is not well understood. There are several invasive and non-invasive treatments available for the problem such as uvulopalatopharyngoplasty, maxillomandibular advancement, upper airway stimulation, use of continuous positive airway pressure and dental appliances. However, these have moderate to poor success rate. The identification of the factors contributing to OSA and development of cause driven treatments are not possible with the existing methods. Therefore, more recently numerical simulations or computational fluid dynamics (CFD)is being used to simulate physiological flow to observe the flow phenomena to help identify the problem causing OSA and derive an effective treatment plan. However, the results of the simulations are highly dependent on the mathematical model, boundary conditions, grid size and so on. Hence, a comparison of simulation results with experimental results is important to validate the accuracy of the simulation results. In-vitro phase-contrast magnetic resonance imaging (PC-MRI) based velocity measurements provides a powerful and non-invasive method to acquire spatially registered fluid velocity. This thesis proposes the use of 2D PC-MRI and 4D flow MRI as an investigative and validation tool for CFD of fluid flow in the upper airway during OSA In the current work, two models are chosen for investigation. One is an idealized rigid axisymmeteric stenosis model with 75% occlusion, which is a narrowing in the arteries resulting from plaque build up and also a simplified version of the occlusion occurring in the anatomically complex pharynx model. This model is primarily used to validate the MRI techniques using previously published laser doppler anemometry (LDA) data and also study the effects and progression of atherosclerosis. The second model is an anatomically accurate and OSA patient individual pharynx model to investigate the flow dynamics in the upper airway during OSA using the above validated 2D PC-MRI and 4D flow MRI. The results are used to understand the cause and effects of OSA. Both 2D PC-MRI and 4D flow MRI are used to measure the velocity in both the models at different boundary conditions. The stenosis model is investigated in laminar and turbulent flow condition. The pharynx model is studied at average inspirational and expiration flow rate. In a statistical framework the results of the velocity measurements in the stenosis and pharynx are compared with computational fluid dynamics (CFD) results to validate the numerical simulation results. Also, with the use of 4D flow MRI other pathophysiological parameters such as wall shear stress and recirculation patterns are quantitatively examined, validated with published data and compared with 2D PC-MRI and CFD data. The role of these parameters in atherosclerosis and OSA are also discussed.