Aortic dissections (AD) are pathological conditions affecting the aorta, characterized by an elevated mortality rate. At present, the pathogenesis of this condition is poorly understood leading to misdiagnosis and major complications. It is believed that the hemodynamics play a crucial role in determining where the aortic dissection will initiate and propagate. Many recent studies implemented numerical simulations to study the hemodynamics patterns and their relationship with clinical outcomes. This work thesis aims at using the Fluid-Structure interaction tool to evaluate the effect of three different pressure levels and two different configurations of the aortic arch (standard and bovine arch) on the flow disturbances and stresses in the aorta that could help determine factors that lead to AD. Flow rate and pressure curves were computed for each condition of interest through the use of a 0D-1D model and then implemented at the surface boundaries of the computational domain. Previous research has demonstrated that tear formation occur in correspondence of elevate wall shear stress (WSS) values; as a consequence the main quantities of interest for this research were the WSS-based descriptors (time average wall shear stress, oscillatory shear index and the relative residence time). Results show that the increase in the pressure causes the maximum principal stress to increase at the wall and determines a higher extension of the areas characterized by elevated OSI values. Both these factors influence the probability of AD initiation and propagation. The geometry configuration had a major impact on the distribution of the flow and structural quantities. The results show that in the standard configuration it is more probable for the AD to develop in the ascending aorta, while for the bovine arch a higher probability is measured in the descending aorta.
La dissezione aortica (AD) è una condizione patologica della parete aortica, che presenta un elevato tasso di mortalità. Attualmente, la patogenesi di questa malattia è poco compresa e ciò è causa di diagnosi mancate e dell’insorgere di gravi complicazioni prima che il personale sanitario possa intervenire. Si ritiene che l’emodinamica aortica giochi un ruolo fondamentale nella formazione e nella propagazione della dissezione aortica. Molteplici studi hanno implementato simulazioni numeriche per studiare i pattern emodinamici e trovare una correlazione con gli outcome clinici. Questo lavoro di tesi si propone di usare simulazioni con interazione fluido-struttura (FSI), per valutare come tre differenti livelli di pressione e due diverse configurazioni (standard e bovine) possano influenzare le regioni in cui la dissezione aortica può svilupparsi. Curve di portate e pressione sono state ottenute mediante un modello 0D-1D, e sono state implementate come condizioni al contorno del dominio computazionale. Diverse ricerche hanno dimostrato che la lacerazione della tunica intima solitamente avviene in area sollecitate da elevati stress di taglio alla parete; di conseguenza gli i descrittori emodinamici relativi agli sforzo di taglio (time average wall shear stress, oscillatory shear index and the relative residence time) rappresentano la quantità di maggiore interesse per questo studio. I risultati mostrano che l’aumento della pressione determina maggiori sforzi alla parete e una più elevata vorticità nel vaso. Entrambi questi fattori determinano la probabilità di poter sviluppare la patologia; si può quindi concludere che la condizione di ipertensione sia la più pericolosa per la AD. La configurazione dell’arco aortico ha un grosso impatto sulla distribuzione dei dati emodinamici e strutturali. I risultati suggeriscono che nella configurazione standard è più probabile che la dissezione aortica si sviluppi nell’aorta ascendente, mentre nella configurazione bovina la probabilità è più alta nell’aorta discendente.
FSI study in a bovine arch geometry with different sets of boundary conditions to identify fluid dynamic patterns that could initiate aortic dissection
Casari, Elisa
2020/2021
Abstract
Aortic dissections (AD) are pathological conditions affecting the aorta, characterized by an elevated mortality rate. At present, the pathogenesis of this condition is poorly understood leading to misdiagnosis and major complications. It is believed that the hemodynamics play a crucial role in determining where the aortic dissection will initiate and propagate. Many recent studies implemented numerical simulations to study the hemodynamics patterns and their relationship with clinical outcomes. This work thesis aims at using the Fluid-Structure interaction tool to evaluate the effect of three different pressure levels and two different configurations of the aortic arch (standard and bovine arch) on the flow disturbances and stresses in the aorta that could help determine factors that lead to AD. Flow rate and pressure curves were computed for each condition of interest through the use of a 0D-1D model and then implemented at the surface boundaries of the computational domain. Previous research has demonstrated that tear formation occur in correspondence of elevate wall shear stress (WSS) values; as a consequence the main quantities of interest for this research were the WSS-based descriptors (time average wall shear stress, oscillatory shear index and the relative residence time). Results show that the increase in the pressure causes the maximum principal stress to increase at the wall and determines a higher extension of the areas characterized by elevated OSI values. Both these factors influence the probability of AD initiation and propagation. The geometry configuration had a major impact on the distribution of the flow and structural quantities. The results show that in the standard configuration it is more probable for the AD to develop in the ascending aorta, while for the bovine arch a higher probability is measured in the descending aorta.File | Dimensione | Formato | |
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Elisa Casari definitivo.pdf
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https://hdl.handle.net/10589/175726