Evaluating the effect of non-Newtonian fluid turbulent flowing for blood within a double-stenosed artery

2021 ◽  
Vol 9 (2) ◽  
pp. 9-19
Author(s):  
Mohammed G. Al-Azawy
Keyword(s):  
Turbulent Viscosity ◽  
Blood Rheology ◽  
Reynolds Stress Model ◽  
Test Model ◽  
Fractional Flow ◽  
Carreau Model ◽  
Flow Reserve ◽  
Stenosed Artery ◽  
Computational Fluid Dynamics Cfd ◽  
O 47

AbstractThis article describes the numerical investigation of blood rheology within an artery that includes two narrowing areas via Computational Fluid Dynamics (CFD) to offer guidance to the community, especially surgeons, and help them to avoid the risk of stenosis. Elliptic blending Reynolds stress model and two models of viscosity have been used in this investigation utilizing STAR-CCM+ 2021.2.1. The test model includes two elliptical stenosis with a 2mm distance between them, and the area of stenosis is 75%. Results of normalized axial velocity, turbulent kinetic energy (TKE) and turbulent viscosity ratio (TVR) were evaluated before, through and after the stenosis in order to predict and avoid the real problems that occur from changing the area of the artery. Furthermore, Fractional flow reserve (FFR) was employed to assess the level of risk of stenosis through the artery, which depends on pressure measurements. Corresponding to the author's observation, it was found that the recirculation regions in the area between the stenosis are larger than the area after the stenosis. Moreover, the results of TKE and TVR are almost identical through and downstream of the stenosis, whereas the TKE is slightly higher with the Carreau model (arrive to 0.54 J/kg) than with the Newtonian flow (arrive to o.47 J/kg) at the upstream and through the first stenosis.

scholarly journals Evaluating the effect of non-Newtonian turbulent blood models within a double-stenosed artery

2021 ◽  
Vol 9 (2) ◽  
pp. 9-19
Author(s):  
Mohammed Ghalib Al-Azawy
Keyword(s):  
Viscosity Ratio ◽  
Turbulent Viscosity ◽  
Blood Rheology ◽  
Reynolds Stress Model ◽  
Test Model ◽  
Fractional Flow ◽  
Carreau Model ◽  
Flow Reserve ◽  
Stenosed Artery ◽  
Computational Fluid Dynamics Cfd

This article describes the numerical investigation of blood rheology within an artery that includes two narrowing areas via Computational Fluid Dynamics (CFD). Elliptic blending Reynolds stress model and two models of viscosity have been used in this investigation utilizing STAR-CCM+ 2021.2.1. The test model includes two elliptical stenosis with a 2mm distance between them, and the area of stenosis is 75%. Results of normalized axial velocity, turbulent kinetic energy (TKE) and turbulent viscosity ratio (TVR) were evaluated before, through and after the stenosis in order to predict and avoid the real problems that occur from changing the area of the artery. Furthermore, Fractional flow reserve (FFR) was employed to assess the level of risk of stenosis through the artery, which depends on pressure measurements. Corresponding to the author's observation, it was found that the recirculation regions in the area between the stenosis are larger than the area after the stenosis. Moreover, the results of TKE and TVR are almost identical through and downstream of the stenosis, whereas the TKE is slightly higher with the Carreau model than with the Newtonian flow at the upstream and through the first stenosis.

scholarly journals Hemodynamic Interference of Serial Stenoses and Its Impact on FFR and iFR Measurements

2019 ◽  
Vol 9 (2) ◽  
pp. 279 ◽  
Author(s):  
Siyeong Ju ◽  
Linxia Gu
Keyword(s):  
Pressure Ratio ◽  
Underlying Mechanism ◽  
Pressure Measurements ◽  
Fractional Flow ◽  
Pressure Distributions ◽  
Flow Reserve ◽  
Spacing Ratio ◽  
Computational Fluid Dynamics Cfd ◽  
Definition Of ◽  
Quantitative Definition

The hemodynamic interference of serial stenoses poses challenges for identifying the functional severity using the fractional flow reserve (FFR) method. The instantaneous wave-free ratio (iFR), i.e., the distal-to-proximal pressure ratio at 75% of diastole, was recently proposed to overcome the disadvantages of the FFR. However, the underlying mechanism remained ambiguous due to the lack of quantitative definition of hemodynamic interference. The objective of this study is to quantitatively define the hemodynamic interference and then examine its role on the FFR and iFR measurements. Pressure distributions, velocity fields, and Q-criterion which identifies vortices, were obtained through the computational fluid dynamics (CFD) for five cases with spacing ratios at 1, 3, 5, 7, and 10. The hemodynamic interference was identified using vortex structures which were quantified by Q-criterion. Results have shown that a spacing ratio of 7 or larger was interference-free. Serial stenoses with a closer spacing ratio led to a larger hemodynamic interference, and thus, larger errors in the FFR measurements compared to the spacing ratio of 7. Moreover, the underestimation of the first stenosis lesion has been observed, even in interference-free cases due to the nature of hyperemia. However, the hemodynamic interference of the serial stenoses has a negligible impact on the iFR measurement, regardless of the spacing ratio. Our results demonstrated that the quantification of the hemodynamic interference in serial stenoses provided a better understanding of its role on the pressure measurements, which could be further exploited for the optimal treatment of serial stenoses.

scholarly journals Numerical Simulation and Clinical Implications of Stenosis in Coronary Blood Flow

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Jun-Mei Zhang ◽  
Liang Zhong ◽  
Tong Luo ◽  
Yunlong Huo ◽  
Swee Yaw Tan ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Gold Standard ◽  
Clinical Implications ◽  
Noninvasive Method ◽  
Fractional Flow ◽  
Porcine Heart ◽  
Clinical Observations ◽  
Flow Reserve ◽  
Invasive Angiography ◽  
Computational Fluid Dynamics Cfd

Fractional flow reserve (FFR) is the gold standard to guide coronary interventions. However it can only be obtained via invasive angiography. The objective of this study is to propose a noninvasive method to determineFFRCTby combining computed tomography angiographic (CTA) images and computational fluid dynamics (CFD) technique. Utilizing the method, this study explored the effects of diameter stenosis (DS), stenosis length, and location onFFRCT. The baseline left anterior descending (LAD) model was reconstructed from CTA of a healthy porcine heart. A series of models were created by adding an idealized stenosis (with DS from 45% to 75%, stenosis length from 4 mm to 16 mm, and at 4 locations separately). Through numerical simulations, it was found thatFFRCTdecreased (from 0.89 to 0.74), when DS increased (from 45% to 75%). Similarly,FFRCTdecreased with the increase of stenosis length and the stenosis located at proximal position had lowerFFRCTthan that at distal position. These findings are consistent with clinical observations. Applying the same method on two patients’ CTA images yieldedFFRCTclose to the FFR values obtained via invasive angiography. The proposed noninvasive computation ofFFRCTis promising for clinical diagnosis of CAD.

scholarly journals Newtonian and Non-Newtonian Blood Rheology Inside a Model of Stenosis

CFD letters ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 27-36
Author(s):  
Mohammed Ghalib Al-Azawy ◽  
Saleem Khalefa Kadhim ◽  
Azzam Sabah Hameed
Keyword(s):  
Blood Flow ◽  
Shear Rate ◽  
Three Dimensional ◽  
Blood Rheology ◽  
Carreau Model ◽  
Newtonian Model ◽  
Importance Factor ◽  
Key Issues ◽  
Computational Fluid Dynamics Cfd ◽  
Artery Disease

In order to imitate the atherosclerosis artery disease and determine the key issues, Computational Fluid Dynamics (CFD) is able to play a leading rule in the analysis of flow physics within the clogged arteries, in particular the stenosis artery. The problem of blood flow blockage through the blood vessel has been investigated numerically within a stenosis artery. In this work, a CFD technique was employed to solve the three-dimensional, steady, laminar and non-Newtonian Carreau model blood flow through a stenosis artery using Star-CCM+ software. The shape of stenosis that has been selected is a trapezoidal with two cases (70% and 90% blockage). Shear rate, streamlines, vorticity and importance factor are examined to assess the influence of non-Newtonian model through the test section, the Carreau model was compared with Newtonian model. The clinical significance of the shear rate is reported for the examined cases, observing that the levels of non-Newtonian model are predicted to be higher in the 90% blockage than that observed within the 70%; the same finding as related with the axial velocity and vorticity. The levels of re-circulation areas and vorticity are showed to be enlarged in the Carreau model compared with the case of Newtonian.

Fractional Flow Reserve: Does a Cut-off Value add Value?

2016 ◽  
Vol 11 (1) ◽  
pp. 17
Author(s):  
Shah R Mohdnazri ◽  
◽  
◽  
◽  
Thomas R Keeble ◽  
...  
Keyword(s):  
Fractional Flow Reserve ◽  
Coronary Intervention ◽  
Grey Zone ◽  
Fractional Flow ◽  
Non Invasive ◽  
Invasive Test ◽  
Flow Reserve ◽  
A Value ◽  
Percutaneous Coronary ◽  
Value Add

Fractional flow reserve (FFR) has been shown to improve outcomes when used to guide percutaneous coronary intervention (PCI). There have been two proposed cut-off points for FFR. The first was derived by comparing FFR against a series of non-invasive tests, with a value of ≤0.75 shown to predict a positive ischaemia test. It was then shown in the DEFER study that a vessel FFR value of ≥0.75 was associated with safe deferral of PCI. During the validation phase, a ‘grey zone’ for FFR values of between 0.76 and 0.80 was demonstrated, where a positive non-invasive test may still occur, but sensitivity and specificity were sub-optimal. Clinical judgement was therefore advised for values in this range. The FAME studies then moved the FFR cut-off point to ≤0.80, with a view to predicting outcomes. The ≤0.80 cut-off point has been adopted into clinical practice guidelines, whereas the lower value of ≤0.75 is no longer widely used. Here, the authors discuss the data underpinning these cut-off values and the practical implications for their use when using FFR guidance in PCI.

Epicardial coronary stenosis severity and myocardial perfusion

2020 ◽  
pp. 12-16
Keyword(s):  
Myocardial Perfusion ◽  
Myocardial Ischemia ◽  
Coronary Disease ◽  
Myocardial Perfusion Reserve ◽  
Pharmacological Intervention ◽  
Fractional Flow ◽  
Perfusion Reserve ◽  
Flow Reserve ◽  
Stenosis Severity ◽  
Microvascular Resistance

Patients suspected of having epicardial coronary disease are often investigated with noninvasive myocardial ischemia tests to establish a diagnosis and guide management. However, the relationship between myocardial ischemia and coronary stenoses is affected by multiple factors, and there is marked biological variation between patients. The ischemic cascade represents the temporal sequence of pathophysiological events that occur after interruption of myocardial oxygen delivery. The earliest part of the cascade is examined via perfusion imaging, and fractional flow reserve (FFR) is a corresponding index which is specific to the coronary artery. Whereas FFR has come to be regarded a clinical reference standard against which other newer invasive and noninvasive tests are validated, the diagnostic FFR threshold for detecting ischemia was established against a combination of noninvasive ischemia tests that assessed different stages of the ischemic cascade. Moreover, the validity of invasive pressure-derived indices of stenosis severity are contingent on the assumption that pressure is proportional to flow if microvascular resistance is constant, a condition induced by pharmacological intervention or by examining specific segments of the cardiac cycle. Furthermore, myocardial perfusion reserve depends on dynamic modulation of microvascular resistance, and dysfunction of the microvasculature can lead to ischemia even in the absence of epicardial coronary disease.

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