Aortic dissection (AD) is a multifactorial disease that affects the aorta. The trigger of AD is the formation of a tear in the wall of the aorta which splits the wall layers allowing blood flows inside it. The propagation of dissection along the wall creates two separate cavities, a true lumen (TL) and a false lumen (FL) divided by a septum. AD is associated with complicated haemodynamics which in turn affects the progression of the disease.
The aim of this project was to analyse flow characteristics and wall shear stress in hypothetical and realistic models with different tear sizes, branch vessel distributions and outlet boundary conditions. First, an idealised model without branches was created to examine the influence of entry and re-entry tear sizes. Four combinations of tear sizes were examined for this purpose. This was followed by an idealised model with branches, for which 30 simulations, with different branch vessel distribution, were performed to evaluate the importance of inflow and outflow capacities of the TL and FL. Finally, a patient-specific model was built based on medical images, and the effects of outlet boundary conditions were investigated.
It was found that pressure difference between the TL and FL, velocities and wall shear stress (WSS) distributions were sensitive to the size of all the tears and their ratio. A balance between the inflow and outflow capacities of the FL reduced the risk of collapse and could help stabilise the dissection. However, increasing the inflow capacity of the TL increased the pressure in the already pressurized lumen, while increasing the outflow capacity reduced the pressure in the TL and may induce TL collapse. Results from the patient-specific model confirmed that the Windkesel outflow boundary condition appeared to be the most promising as it correctly predicted a reduction of flow into the TL branches and a significant increase of flow into the FL branch, in accordance with the in vivo observation. However, the predicted flow patterns, WSS distributions and pressure differences were not particularly sensitive to the type of outflow boundary conditions employed.