Hesaplamalı akışkanlar dinamiğinin kardiyovasküler hastalıkların hemodinamik incelemesinde uygulanması: Serebral anevrizma ve fontan dolaşımında bozukluk

Cardiovascular disease is the combination of diseases that involve blood vessels or heart and it is the number one cause of death all over the world. Cerebrovascular disease and congenital heart defects are types of cardiovascular diseases. Among many other physiological systems cardiovascular system gets more attention from researchers and computational modeling of this system is one of the most popular research area. Hemodynamic parameters have a great role on disease formation and growth due to this fact understanding the underlying mechanisms behind flow characteristics is important and used in treatment and diagnostics of diseases. There are wide range of computational fluid dynamic (CFD) studies conducted on cardiovascular system over several decades. Quantifying the flow field and hemodynamic parameters in geometries related to cardiovascular diseases and using the results to improve the treatment procedures for the specific disease is the main motivation of this study. In this study CFD is used to evaluate important hemodynamic parameters and comparison of different flow fields for geometries related to two different cardiovascular diseases; cerebral aneurysm and failure of Fontan circulation. For the palliative repair of single-ventricle congenital heart defects, the hemodynamic energy loss of the surgical conduit determines the post-operative cardiac output and exercise capacity, as demonstrated by recent clinical studies. In this study, the hemodynamic energy loss of severely deformed surgical pathways due to torsional deformation and anastomosis offset are investigated. A mock-up total cavopulmonary connection circuit is designed to replicate the mechanically failed Inferior Vena Cava (IVC) anastomosis morphologies under physiological venous pressure (9, 12, 15 mmHg), in vitro, employing the commonly used conduit materials: PTFE, Dacron, and porcine pericardium. The sensitivity of hemodynamic performance to torsional deformation for 3 different twist angles (0°, 30°, 60°) and 3 different caval offsets (0Diameter, 0.5D and 1D) are digitized in three dimensions and employed in computational fluid dynamic simulations to determine the corresponding hydrodynamic efficiency levels. A total of 81 deformed conduit configurations are analyzed; the pressure drop values increased from 80 to 1070 % with respect to the ideal uniform diameter IVC conduit flow. The investigated surgical materials resulted in significant variations in terms of flow separation and energy loss. For example, the porcine pericardium resulted in a pressure drop that was 8 times greater than the Dacron conduit. Likewise, PTFE conduit resulted in a pressure drop that was 3 times greater than the Dacron conduit under ivthe same venous pressure loading. If anastomosis twist and/or caval offset cannot be avoided intraoperatively due to the anatomy of the patient, alternative conduit materials with high structural stiffness and less influence on hemodynamics can be considered. Cerebral or intracranial aneurysms are localized dilation of local vessel wall and their rupture can result in stroke and death with a 60% mortality rate. Aneurysms can be detected by using present imaging techniques and experts should decide whether to leave the aneurysm or apply a treatment, because the risks of the current treatment methods can exceed the risk of aneurysm rupture. It is very important to find the riskiest unruptured aneurysm before taking the procedural risks. It is speculated that intra-aneurysmal hemodynamics i.e. forces resulting of the blood flow itself is the more important factor rather than morphology in both pathogenesis and thrombosis of cerebral aneurysm. A fully understanding of relation between blood flow characteristics and rupture risk is very important before deciding on treatment due to its important role in the mechanism of initiation, growth, and rupture. In this study 5 patient specific geometries with saccular aneurysms which is the most common form of cerebral aneurysm, are gathered as Digital Imaging and Communication in Medicine (DICOM) data. Among them anonymously one of them was already rupture. The aim of the study is to investigate the flow hemodynamics inside 5 different patient specific aneurysms and determine the rupture by using flow characteristics data gathered from the CFD simulations. The important aspect of the study is the obscurity of the ruptured geometry, results and discussion are written while the ruptured case is still unknown. Ruptured case will be identified in International Aneurysm CFD Challenge 2015 manuscript which will be published in 2016. Parameters such as wall shear stress contours, velocity streamlines, average surface area of the aneurysm, average volume of the aneurysm, maximum length of the aneurysm and mean wall shear stress levels are evaluated and analyzed. Hemodynamic parameters for all five cases resulted distinctively. thus, rupture case is selected by hypothesizing that aneurysm rupture is associated with low wall shear stress with disturbed flow field and had small impingement region on the surface.