The Hemodynamics Of Carotid Arteries After Carotid Endarterectomy And The Effects Induced By Their Geometric Features

Background: Carotid atherosclerotic disease is highly related to cerebrovascular events.Carotid endarterectomy is the common operation method to treat this disease. Flow andloading conditions are compared between treated and untreated carotid arteries to evaluatethe advantages of different surgical procedures. The influence of the angle between theinternal and external carotid arteries on the hemodynamics is also discussed.Methods: Patient-specific models are reconstructed from MDCT data. Intraoperativeultrasound flow measurements are performed on the treated carotid arteries and theobtained data are used as the boundary conditions of the models and the validations of thecomputational results. Finite volume method is employed to solve the transport equationsand the flow and loading conditions of the models are reported.Results: The results of first part indicate that:(i) in two of the three patients, theinternal-to-external flow rate ratio in the untreated carotid artery is larger than that in thetreated one, and the average overall flow split ratio by summing up the data of both theleft and right carotid arteries is about2.15;(ii) in the carotid arteries without seriousstenosis, the maximum velocity magnitude during mid-diastole is32~37%of that atsystolic peak, however, in the carotid artery with50%stenosis by hard plaques, this value isnearly doubled (64%);(iii) in the carotid bulb, high wall shear stress occurs at thebifurcation near the external carotid artery in all of the cases without hard plaques;(iv) hightemporal gradient of wall shear stress (>35Pa/s) is shown in the narrowing regions alongthe vessels;(v) the operated arteries present low time-averaged wall shear stress at thecarotid bulb, especially for the treated arteries with patch technique, indicating thepossibility of the recurrence of stenosis.The results of second part indicate that: systolic peak of the eversion carotidendarterectomy model showed a gradually decreased pressure along the stream path, theconventional carotid endarterectomy model revealed high pressure (about180Pa) at thecarotid bulb. Regions of low wall shear stress in the conventional carotid endarterectomymodel were much larger than that in the eversion carotid endarterectomy model and withlower TAWSS values (conventional carotid endarterectomy:0.03–5.46Pa vs. eversioncarotid endarterectomy:0.12–5.22Pa).The results of third part indicate that:(i) the volume flow rate ratio of internal-to-external carotid artery decreases while the external-to-common carotid arteryangle and the internal-to-common carotid artery angle increase;(ii) the enlargement of theangle (either external-to-common carotid artery angle or internal-to-common carotid arteryangle) can reduce the region of low time-averaged wall shear stress (<0.3Pa) on the affectedinternal or external carotid artery, a positive effect to protect further plaque formations; and(iii) changing of the bifurcation angle presents little effects on the velocity, pressure andwall shear stress distributions in the carotid artery.Conclusions: The computational work quantifies flow and loading distributions in thetreated and untreated carotid arteries of the same patient, contributing to evaluation of theoperative results and indicating the recurrent sites of potential plaques. The second partindicated that computational fluid dynamics after conventional carotid endarterectomy andeversion carotid endarterectomy disclosed differences in hemodynamic patterns. Largerstudies are necessary to assess whether these differences are consistent and might explaindifferent rates of restenosis in both techniques. The third part establishes twothree-dimensional patient-specific models of the carotid artery. By changing the bifurcationangle while keeping the physiological morphology of the carotid artery, we investigate thehemodynamic variations and discuss their relationships to atherosclerosis.