Haemodynamic Analysis of the Relationship between the Morphological Alterations of the Ascending Aorta and the Type A Aortic-Dissection Disease

Type A aortic dissection(AD)is one of the most serious cardiovascular diseases,whose risk predictors are controversial.The purpose of this research was to investigate how elongation accompanied by dilation of the ascending aorta(AAo)affects the relevant haemodynamic characteristics using image-based computational models.Five elongated AAos with different levels of dilation have been reconstructed based on the centerlines data of an elderly and an AD patient.Numerical simulations have been performed assuming an inflow waveform and a Windkessel model with three elements for all outflow boundaries.The numerical results have revealed that the elongation of AAo can disturb the systolic helical flow pattern between the root of AAo and the aortic arch.The helical flow inside the AAo starts to develop into a vortex flow when the elongated AAo becomes dilated.The vortex gives rise to a localized oscillatory shear index at the ostia of the brachiocephalic artery(BA)and the inner curve of the aortic arch.This study suggests that abnormal growth of AAo,especially accompanied by its moderate dilation,can be considered as morphological risk factors of AD.

THE EFFECTS OF PHYSIOLOGICAL FLOW WAVEFORM ON WALL SHEAR STRESS IN CAROTID BIFURCATION MODEL

Numerical models of carotid bifurcation were constructed using a combination of tuning-fork bifurcation and straight or curved common carotid. The different inlet velocity profiles of the common carotid were generated for Bloch flow waveform and Holdsworth flow waveform, respectively. The effects of the different flow waveform for the common carotid on Wall Shear Stress （WSS） and Oscillatory Shear Index （OSI） of carotid bifurcation were studied by CFD method. The results show that the physiological flow waveform of curved common carotid has a significant effect on OSI. In particular, the OSI on the outer walls of carotid sinus and external carotid becomes higher in the inward-curved common carotid for Holdsworth flow waveform. But, in both cases of low WSS and high OSI, the effects of flow waveforms are smaller than those of the curved common carotid. The study reveals that the exact knowledge of the physiological flow waveform, vascular geometry and inlet velocity profile is important for hemodynamic numerical simulation of artery bifurcation.

Enhanced External Counterpulsation Inducing Arterial Hemodynamic Variations and Its Chronic Effect on Endothelial Function

To make clear the precise hemodynamic mechanism underlying the anti-atherogenesis benefit of enhanced external couterpulsation(EECP) treatment, and to investigate the proper role of some important hemodynamic factors during the atherosclerotic progress, a comprehensive study combining long-term animal experiment and numerical solving was conducted in this paper. An experimentally induced hypercholesterolemic porcine model was developed and the chronic EECP intervention was subjected. Basic hemodynamic measurement was performed in vivo, as well as the arterial endothelial samples were extracted for physiological examination. Meanwhile, a numerical model was introduced to solve the complex hemodynamic factors such as WSS and OSI. The results show that EECP treatment resulted in significant increase of the instant levels of arterial WSS, blood pressure, and OSI. During EECP treatment, the instant OSI level of the common carotid arteries over cardiac cycles raised to a mean value of 8.58 ×10-2±2.13 ×10-2. Meanwhile, the chronic intervention of EECP treatment significantly reduced the atherosclerotic lesions in abdominal aortas and the endothelial cellular adherence. The present study suggests that the unique blood flow pattern induced by EECP treatment and the augmentation of WSS level in cardiac cycles may be the most important hemodynamic mechanism that contribute to its anti-atherogenesis effect. And as one of the indices that cause great concern in current hemodynamic study, OSI may not play a key role during the initiation of atherosclerosis.

Numerical simulation to study the impact of compliance mismatch between artificial and host blood vessel on hemodynamics

Small-diameter artificial blood vessels are prone to cause intimal hyperplasia(IH)after transplantation,which leads to restenosis and low long-term patency rates.The main biomechanical factor for IH formation is the compliance mismatch between the artificial and host blood vessels which can cause abnormal hemodynamics.Although there have been many studies on vascular compliance mismatches,however,little attention has been paid to the effect of the degree of compliance mismatch between graft and the host vessel on hemodynamics.At present,the research on compliance mismatch between the artificial and host blood vessels is still very limited,especially with regard to the specific impact of the compliance mismatch degree on hemodynamics.Therefore,three end-to-end anastomosis models(the compliance of the artificial blood vessel is lower than,similar to,and higher than that of the host blood vessel,called model 1,model 2,model 3,respectively)were constructed and simulated in this study.Simulation results showed that the radial displacement difference between the artificial and host blood vessels were 0.281 mm,0.183 mm and 0.485 mm in model 1,model 2 and model 3,respectively.A low-velocity recirculation zone near the distal anastomosis was formed in model 1 which resulted in excessively low TAWSS(9.261 E-5Pa)and high OSI(0.497).Similarly,a low-velocity recirculation zone near the proximal anastomosis was formed in model 3 and lead to low TAWSS(6.007 E-4Pa)and high OSI(0.480).However,there was no low-velocity recirculation zone near the anastomosis stoma in model 2.The results are instructive for the design and preparation of artificial blood vessels.

Pulsatile blood flow through stenosed artery with axial translation

The study of pulsatile blood flow through axisymmetric stenosed artery subject to an axial translation has been attempted with hematocrit concentration-dependent blood viscosity. The heart contraction and subsequent relaxation generate periodic pressure gradient in blood flow and translation in the artery can be represented by Fourier series. Numerical data required for computing Fourier harmonics for the pressure gradient and acceleration in the artery has been simulated from pressure waveform graph and biplanar angiogram. Velocity field has been obtained by solving governing equation using variational Ritz method. The hemodynamic indicators WSS, AWSS, OSI, RRT are derived and computed numerically. The effects of thickness of stenosis, and hematocrit concentration index on these indicators are computed and analyzed through graphs.