A Study On Hemodynamic Risk Factors For Ischemic Stroke In Carotid Atherosclerotic Disease Patients

Background and Purpose: Hemodynamic factors play an important role in the occurrence and development of carotid atherosclerosis, therefore computational fluid dynamics(CFD) provides possibilities for the assessment of stroke risk of patients with carotid artery stenosis. However, the accuracy of calculations in CFD depends on the precision of boundary conditions, such as outlet pressure, which is difficult to measure directly. We hereby propose a new method that calculates the blood flow distribution according to the principle of minimal energy loss(MEL), in order to optimize the setting of outlet boundary conditions in carotid artery stenosis CFD studies.Methods: Twenty-two carotid arteries with varied stenosis in 17 patients admitted in our centre from June 2014 to December 2014 were included in this study according to our criteria of selection and exclusion. Numerical models were built based on CTA data of the patients, blood flow velocities of certain sections of the common carotid artery, internal carotid artery and external carotid artery of patients were acquired via Doppler ultrasonography. Using the ANSYS CFX software, we set the inlet condition according to the mass flow-rate calculated from the Doppler velocity measurement, and calculate the blood volume ratio between internal carotid artery and common carotid artery(Qica/Qcca) by setting the outlet conditions as traction-free pressure or, alternatively, minimal energy loss points. We calculate Qica/Qcca by ratio of area stenosis, Groen's empirical formula and clinical Doppler ultrasonographic measurements. Errors in the estimates of Qica/Qcca were obtained by various methods, and statistical analyses were conducted with reference to the Qica/Qcca from Doppler examinations.Results: The discrepancy between minimal energy loss points and clinical measurements is 9.39±4.83%, the discrepancy of Qica/Qcca under traction-free boundary is 13.8±9.88%, and the discrepancy of Qica/Qcca by using ratio of area stenosis and Groen empirical formula is 15.97±13.54%. The error in Qica/Qcca calculated by MEL points was less than that obtained from traction-free conditions(p=0.455) and Groen empirical formula(p=0.102), but shows no statistically significant difference. For mild stenosis patients, the error in Qica/Qcca under tractionfree boundary is 7.03±2.61%, and the error by minimal energy loss is 7.46±3.29%. There is no statistically significant difference between the two(p=1.0). However, as stenosis increases, the error associated with the traction-free boundary condition increases dramatically. When the carotid artery has moderate or severe stenosis(50-99%), the error under tractionfree boundary conditions is 18.49±10.39%, while the error from MEL point calculation is 11.05±5.1%. There is a statistically significant difference(p=0.045), with the latter being less than the former.Conclusion: It is feasible to perform hemodynamic analyses by using traction-free outlet boundary condition when there is no stenosis or mild stenosis in carotid artery, but the error in blood flow distribution increases dramatically by using traction-free boundary when there is moderate or severe stenosis in the carotid artery. The minimal energy loss theory can optimize the setting of outlet boundary conditions in hemodynamic analyses.Purpose: To assess the effects of non-patient specific inlet boundary condition on the calculation results of various hemodynamic parameters.Methods: Six numerical models of moderate carotid artery stenosis were built based on CTA images of the six patients. Flow parameters were calculated using computational fluid dynamics(CFD). We compared the wall shear stress(WSS), normalized wall shear stress(NWSS), pressure, energy loss per unit volume(ELv), and pressure loss coefficient(PLc) using different inlet boundary conditions: 300ml/min, 400ml/min and 500ml/min respectively according to previous literature.Results: Inlet boundary conditions exert an effect on the estimates of hemodynamic parameters. For the range of blood flow rates studied, every increase of 100ml/min of inlet blood flow volume leads to an average increase of 1.293 Pa in WSS of the stenosis section, corresponding to a change of 29.48% compared to the average WSS; the NWSS makes an average change of 0.1611, correspongding to 6.64%; the pressure in the stenosis section makes an average increase of 55.877 Pa, correspongding to 26.61%; the EL makes an average increase of 2154.37W/m3, correspongding to 50.83%; and the PLc makes an average change of 0.942, correspongding to a relative change of 9.59% in its value.Conclusion: Estimates of hemodynamic parameters from CFD exhibit a diverse range of sensitivities to the changes in the inlet boundary conditions. The estimates of WSS, pressure, and ELv change more significantly than NWSS and PLc, while the inlet boundary condition was varied. When using non-patient specific inlet boundary conditions for hemodynamic analyses, we found that the evaluation reliability of NWSS and PLc is better than WSS, pressures and ELv.Background and Purpose: Hemodynamic factors play an important role in the occurrence and development of atherosclerosis; however, the relevant hemodynamic risk factors of ischemic stroke in carotid atherosclerotic diseases are still not clear. This study used patient-specific numerical models to explore the hemodynamic risk factors of ischemic stroke in patients with moderately stenosed atherosclerotic carotid arteries.Methods: Twenty-four moderately stenosed carotid arteries of 15 patients admitted in the out-patient and in-patient departments of neurosurgery, Changhai Hospital, from January 2013 to December 2014 were included in this study. Patients were divided into a non-symptom group(n=11) and a symptom group(n=13) based on their previous cerebral infarction symptoms and MRI results. Numerical models were built based on CTA data of the patients and hemodynamic analyses were conducted using ANSYS CFX. Different hemodynamic parameters such as normalized wall shear stress(NWSS), energy loss per unit volume(ELv), and pressure loss coefficient(PLc) were obtained. Statistical analyses were conducted to explore the hemodynamic risk factors of ischemic stroke in these patients.Results: The NWSS of the stenosis section is 3.60±1.87 Pa in the symptom group, and 2.35±0.70 Pa in non-symptom group, the former being higher than the latter with a statistically significant difference(p=0.048); the PLc in the symptom group is 13.01±6.62, while that of the non-symptom group is 7.93±4.46, the former being higher than the latter with a statistically significant difference(p=0.042); and the ELv in the symptom group(4945.67±2905.33w/m3) is higher than that in the nonsymptom group(3710.65±1811.82w/m3), but without statistically significant difference(p=0.219).Conclusion: Hemodynamic factors are important causes of ischemic stroke in carotid atherosclerotic diseases. High NWSS and PLc are related to high risk of ischemic stroke in patients with moderately stenosed atherosclerotic carotid arteries.