Blood flow analysis of the aortic arch using computational fluid dynamics in a coupled 3D-0D framework

Regions of the aortic arch affected by an aneurysm or dissection may require surgical intervention using vascular grafts, which includes a means of re-perfusing the supra-aortic branch vessels, comprised of the left subclavian artery (LSA), left common carotid artery (LCCA) and brachiocephalic artery. Open surgical grafts are widely used in this arch reconstruction. During open surgical repair, it is crucial that branch vessel revascularisation occurs quickly and with a graft configuration that promotes physiological perfusion, to prevent neurologic and cardiac events through ischaemia. It is clear, therefore, that enhanced understanding of perfusion in patient-specific cases is critical to improving clinical practice and patient outcomes. In this work, a representative computational model of the aortic arch was investigated via computational fluid dynamics methods to analyse the haemodynamics of a human aortic arch using a coupled 3D-0D numerical framework. To create patient-specific boundary conditions, the zero dimensional, 3-element Windkessel (3EWM) model was coupled to the 3-dimensional geometry at each branch outlet. Consequently, through implementation of different resistance and compliance to represent the peripheral vasculature, this enabled simulation of a range of physiologically realistic downstream conditions, both healthy and pathological. The 3EWM is computationally efficient, does not require any specification of pressure or flow rate at the outlet, and effectively describes the pressure-flow relation due to the distal vasculature. In addition to flow rate, and therfore perfusion, other haemodynamic parameters under investigation include time averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and pressure distribution. These are clinically significant in the case of open surgical vascular grafts as an abnormal distrubtion can increase the risk of graft failure through platelet activation and thrombosis, and focal development of post-surgical intimal hyperplasia at regions of anastomosis. To conclude, a patient specific model which includes the post-surgical aortic geometry in combination with patient-specific Windkessel boundary conditions allows one to predict the flow rate through different branches of the aortic arch, thereby optimising peripheral organ perfusion and minimising long-term risk of neurologic and cardiac events.