• Korea-Australia Rheology Journal
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• v.21 no.1
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• pp.39-46
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• 2009

Atherosclerosis is a disease that narrows, thickens, hardens, and restructures a blood vessel due to substantial plaque deposit. The geometric models of the considered stenotic blood flow are three different types of constriction of cross-sectional area of blood vessel; 25%, 50%, and 75% of constriction. The computational model with the fluid-structure interaction is introduced to investigate the wall shear stresses, blood flow field and recirculation zone in the stenotic vessels. The velocity profile in a compliant stenotic artery with various constrictions is subjected to prescribed physiologic waveform. The computational simulations were performed, in which the physiological flow through a compliant axisymmetric stenotic blood vessel was solved using commercial software ADINA 8.4 developed by finite element method. We demonstrated comparisons of the wall shear stress with or without the fluid-structure interaction and their velocity profiles under the physiological flow condition in the compliant stenotic artery. The present results enhance our understanding of the hemodynamic characteristics in a compliant stenotic artery.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.227-236
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• 1994

Steady flows of Newtonian and non-Newtonian fluids in the stenotic tubes with various stenotic shapes are numerically simulated. Validity of the modified power-law model as a constitutive equation for the purely viscous non-Newtonian fluid is discussed and the results of the power-law model are compared with those of the Carreau model, the Powell-Eyring model and experimental data for blood. Flow characteristics and reattachment lengths for non-Newtonian fluids in the stenotic tubes are presented extensively. Also, the analysis is extended to predict the influences of diameter ratio, stenosis spacing, number of stenosis and Reynolds number on the flow characteristics in the multiple stenotic tubes.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.2
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• pp.140-146
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• 2014

Stenosis is the drastic reduction in the cross-sectional area of blood vessel caused by accumulations of cholesterol. It affects the blood flow property and structure from the fluid dynamic point of view. To understand the flow phenomenon more clearly, a particle image velocimetry method is used and the fluid dynamic characteristics in a circular channel containing stenosis structure is investigated experimentally in this study. Different stenotic-structured models made of acrylic material are subjected to a pulsatile flow generated by an in-house designed pulsatile pump. The inner diameter of the tube inlet is 20 mm and the length of reduced area for stenosis ranges between 35mm and 40mm. It is circulated continuously through a circular channel by the pump system. Pressure is measured at four different sections during systolic and diastolic phase changes. The phase-averaged velocity field distribution shows a recirculation regime after the stenotic structure. The effects of the stenotic obstructions are found to be more severe when the aspect ratio is varied.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.11
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• pp.891-896
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• 2008

In the present computational study, simple stenotic artery models using pulsatile flow condition were investigated. A 1 Hz non-reversing sinusoidal velocity for pulsatile flow was imposed at the flow inlet and the corresponding Womersley number based on the vessel radius is 2.75. The simple stenotic geometries have been used that consist of 25%, 50% and 75% semicircular constriction in a cylindrical tube. In this paper, numerical solutions are presented for a first harmonic oscillatory flow using commercial software ADINA 8.4. As stenosis and Reynolds number increase, the maximum wall shear stress(WSS) increases while the minimum WSS decreases. As the stenotic rate increases, the pressure drop at the throat severely decreases to collapse the artery and plaque. It is found that the fluid mechanical disturbances due to the constriction were highly sensitive with rate of stenosis and Reynolds number. When Reynolds number and stenosis increase, the larger recirculation region exists. In this recirculation region the possibility of plaque attachment is increasingly higher. The present results enhance our understanding of the hemodynamics of a stenotic artery.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1603-1612
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• 1996

The pressure loss coefficient of Newtonian and non-Newtonian fluids such as water, aqueous solutions of Carbopol-934 and Separan AP-273 and blood in the stenotic tubes are determined experimentally and numerically. The numerical analyses for flows of non-Newtonian fluids in the stenotic tubes are conducted by the finite element method. The effect of the contraction ratio and the ratio of length to diameter on the pressure drop are investigated by the experiments and numerical analysis. The pressure loss coefficients are significantly dependent upon the Reynolds number in the laminar flow regime. As Reynolds number increases, the pressure loss coefficients of both Newtonian and non-Newtonian fluids decrease in the laminar flow regime. As the ratio of length to diameter increases the maximum pressure loss coefficient increases in the laminar flow regime for both Newtonian and non-Newtonian fluids. Newtonian fuid shows the highest values of pressure loss coefficient and blood the next, followed by Carbopol solution and Separan solution in order. Experimental results are used to verify the numerical analyses for flows of Newtonian and non-Newtonian fluids. Numerical results for the maximum pressure loss coefficient in the stenotic tubes are in fairly good agreement with the experimental results. The relative differences between the numerical and experimental results of the pressure loss coefficients in the laminar flow regime range from 0.5% to 14.8%.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.385-388
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• 2008

The objective of this paper is simulating blood flow through the branched and stenotic tube numerically. SC-Tetra, which is one of the commercial code using FVM method, was utilized for this analysis. The flow is assumed as an incompressible laminar flow with the additional condition of non-Newtonian fluid. As the constitutive equation for the fluid viscosity, the following models were solved with governing equations ; Cross Model, Modified Cross Model, Carreau Model and Carreau-Yasuda Model. Final goal was achieved to get analytic data about shear stress, at specific points, changing the geometry with various factors like the bifurcation angle, diameter of the branches, the ratio of stenosis, and etc. The material property of blood was referred from the related papers. Furthermore, to verify results they were compared with those of the published papers. There were some discrepancies based on the different solver and the different data post-processing method. However, many parameters like the location of low shear stress, which arised from bifurcation or stenosis, and the tendency of various factors were found to be very similar.

• International Journal of Vascular Biomedical Engineering
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• v.2 no.1
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• pp.25-30
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• 2004

Catheters are used to measure translesional pressure gradients in the stenosed coronary arteries. Uses of catheters during coronary angioplasty cause flow obstructions. A narrowed flow cross section with catheter effectively introduced a tighter stenosis than the enlarged residual stenoses after balloon angiplasty. Catheters in blood vessels cause pressure gradient rise and blood flow drop during the measurements. In this study, three dimensional computer simulations are conducted to investigate the flow blockage effects due to the catheter obstructions during the coronary angioplasty. The computer simulation models are generated by the data, which are measured by coronary angiogram, and the blood is treated as non-Newtonian fluid. The velocity, pressure, and wall shear stress variations are observed for the estimate of damages of blood vessel. This study is also extended to investigate the effects of stenotic vessel size, and shape and catheter size and location.

• Journal of Korean Neurosurgical Society
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• v.54 no.4
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• pp.280-288
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• 2013

Objective : Perfusion computed tomography (PCT) has the ability to measure quantitative value and produce maps of mean transit time (MTT), cerebral blood flow (CBF), and cerebral blood volume (CBV). We assessed cerebral hemodynamics by using these parameters and acetazolamide (ACZ) challenge for pre- and post-procedural evaluation in patients with unilateral cerebrovascular stenotic disease. Methods : Thirty patients underwent pre-procedural PCT with ACZ challenge, and 24 patients (80%) was conducted follow up PCT after angioplasty with same protocol. The mean MTT, CBF, and CBV were measured and compared in both middle cerebral arterial (MCA) territories before and after ACZ challenge. Hemispheric ratio and percent change after ACZ challenge were calculated before and after angioplasty. Results : The mean stenosis rate was 76.6%. Significant increases in MTT (32.6%, p=0.000) and significant decreases in CBF (-14.2%, p=0.000) were found in stenotic side MCA territories. After ACZ challenge, there were significant changes in MTT (37.4%, p=0.000), CBF (-13.1%, p=0.000), and CBV (-10.5%, p=0.001) in pre-procedural perfusion study. However, no significant increases were found in MTT, or decreases in CBF and CBV in post-procedural study. There were no significant changes after ACZ challenge also. In addition, the degrees of these changes (before and after ACZ challenge) were highly correlated with the stenotic degrees in pre-procedural perfusion study. Conclusion : PCT with ACZ challenge appears to be a useful tool to assess the cerebral perfusion status especially in patients with unilateral symptomatic stenotic disease.

• Journal of Cardiovascular Imaging
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• v.30 no.3
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• pp.169-180
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• 2022

BACKGROUND: We analyzed whether C-11 acetate positron emission tomography (PET) can be used for the evaluation of non-infarct-related artery (NIRA) in patients with ST-elevation myocardial infarction (STEMI) and multivessel disease. METHODS: We prospectively enrolled 31 patients with STEMI and at least one NIRA stenosis (diameter stenosis [DS] ≥ 50%). C-11 acetate PET was performed after successful revascularization for the infarct-related artery (IRA). Myocardial blood flow (MBF) and oxidative metabolism (k_mono) were measured and compared between NIRA vs. IRA, stenotic (DS ≥ 50%) vs. non-stenotic (DS < 50%) NIRAs, and NIRAs with significant stenosis (DS ≥ 70% or fractional flow reserve [FFR] ≤ 0.80) vs. those without (neither DS ≥ 70% nor FFR ≤ 0.80). The correlations between PET and angiographic parameters were also analyzed. RESULTS: MBF and k_mono were significantly higher in NIRAs than those in IRAs. Stenotic NIRAs showed significantly reduced stress MBF, myocardial flow reserve (MFR), relative flow reserve (RFR) (0.72 ± 0.12 vs. 0.82 ± 0.14; p = 0.001), and stress k_mono, as compared to those in non-stenotic NIRAs. NIRAs with significant stenosis had significantly lower stress MBF, MFR, and RFR (0.70 ± 0.10 vs. 0.80 ± 0.14; p = 0.001). RFR showed the best, but modest linear correlation with DS of NIRA stenosis (r = -0.429, p = 0.001). RFR > 0.81 could effectively exclude the presence of significant NIRA stenosis. CONCLUSIONS: C-11 acetate PET could be a feasible alternative noninvasive modality in patients with STEMI and multivessel disease, by excluding the presence of significant NIRA stenosis.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.10-16
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• 2019

Considering the role of viscosity in the hemorheology, the characteristics of non-Newtonian fluid are important in the pulsatile blood flows. Stenosis, with an abnormal narrowing of the vessel, contributes to block blood flows to downstream tissue and lead to plaque rupture. Therefore, systematic analysis of blood flow around stenosed vessels is crucial. In this study, non-Newtonian behaviors of blood analog fluids around the micro-stenosis with 60 % severity in diameter of $500{\mu}m$ was examined by using CFX under the pulsatile flow conditions with the period of 10 s. Viscosity information of two non-Newtonian fluids were obtained by fitting the value of normal blood and highly viscous blood. As the Newtonian fluid, the water at room temperature was used. During the pulsatile phase, wall shear stress (WSS) is highly oscillated. In addition, high viscous solution gives rise to increases the variation in the WSS around the micro-stenosis. Highly oscillating WSS enhance increasing tendency of plaque instability or rupture and damage of the tissue layer. These results, related to the influence on the damage to the endothelium or stenotic lesion, may help clinicians understand relevant mechanisms.