scholarly journals Virtual FFR Quantified with a Generalized Flow Model Using Windkessel Boundary Conditions

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Keltoum Chahour ◽  
Rajae Aboulaich ◽  
Abderrahmane Habbal ◽  
Nejib Zemzemi ◽  
Chérif Abdelkhirane
Keyword(s):  
Boundary Conditions ◽  
Flow Model ◽  
Fluid Model ◽  
Invasive Procedure ◽  
Navier Stokes ◽  
Fractional Flow ◽  
Flow Reserve ◽  
Arbitrary Position ◽  
Model Versus ◽  
Good Agreement

Fractional flow reserve (FFR) has proved its efficiency in improving patient diagnosis. In this paper, we consider a 2D reconstructed left coronary tree with two artificial lesions of different degrees. We use a generalized fluid model with a Carreau law and use a coupled multidomain method to implement Windkessel boundary conditions at the outlets. We introduce our methodology to quantify the virtual FFR and conduct several numerical experiments. We compare FFR results from the Navier–Stokes model versus generalized flow model and for Windkessel versus traction-free outlet boundary conditions or mixed outlet boundary conditions. We also investigate some sources of uncertainty that the FFR index might encounter during the invasive procedure, in particular, the arbitrary position of the distal sensor. The computational FFR results show that the degree of stenosis is not enough to classify a lesion, while there is a good agreement between the Navier–Stokes model and the non-Newtonian flow model adopted in classifying coronary lesions. Furthermore, we highlight that the lack of standardization while making FFR measurement might be misleading regarding the significance of stenosis.

A Two-Dimensional Potential Flow Model of the Wave Field Generated by a Semisubmerged Body in Heaving Motion

1988 ◽  
Vol 32 (02) ◽  
pp. 83-91
Author(s):  
X. M. Wang ◽  
M. L. Spaulding
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Potential Flow ◽  
Flow Model ◽  
Second Order ◽  
Two Dimensional ◽  
Third Order ◽  
The Third ◽  
Potential Flow Model ◽  
Good Agreement

A two-dimensional potential flow model is formulated to predict the wave field and forces generated by a sere!submerged body in forced heaving motion. The potential flow problem is solved on a boundary fitted coordinate system that deforms in response to the motion of the free surface and the heaving body. The full nonlinear kinematic and dynamic boundary conditions are used at the free surface. The governing equations and associated boundary conditions are solved by a second-order finite-difference technique based on the modified Euler method for the time domain and a successive overrelaxation (SOR) procedure for the spatial domain. A series of sensitivity studies of grid size and resolution, time step, free surface and body grid redistribution schemes, convergence criteria, and free surface body boundary condition specification was performed to investigate the computational characteristics of the model. The model was applied to predict the forces generated by the forced oscillation of a U-shaped cylinder. Numerical model predictions are generally in good agreement with the available second-order theories for the first-order pressure and force coefficients, but clearly show that the third-order terms are larger than the second-order terms when nonlinearity becomes important in the dimensionless frequency range 1≤ Fr≤ 2. The model results are in good agreement with the available experimental data and confirm the importance of the third order terms.

scholarly journals Numerical simulation of the fractional flow reserve (FFR)

2018 ◽  
Vol 13 (6) ◽  
pp. 57 ◽  
Author(s):  
Keltoum Chahour ◽  
Rajae Aboulaich ◽  
Abderrahmane Habbal ◽  
Cherif Abdelkhirane ◽  
Nejib Zemzemi
Keyword(s):  
Fractional Flow Reserve ◽  
Flow Model ◽  
Rigid Wall ◽  
Fractional Flow ◽  
Wall Model ◽  
Factors Affecting ◽  
Non Invasive ◽  
Flow Reserve ◽  
Weakly Coupled ◽  
Preliminary Study

The fractional flow reserve (FFR) provides an efficient quantitative assessment of the severity of a coronary lesion. Our aim is to address the problem of computing non-invasive virtual fractional flow reserve (VFFR). In this paper, we present a preliminary study of the main features of flow over a stenosed coronary arterial portion, in order to enumerate the different factors affecting the VFFR. We adopt a non-Newtonian flow model and we assume that the two-dimensional (2D) domain is rigid in a first place. In a second place, we consider a simplified weakly coupled FSI model in order to take into account the infinitesimal displacements of the upper wall. A 2D finite element solver was implemented using Freefem++. We computed the VFFR profiles with respect to different lesion parameters and compared the results given by the rigid wall model to those obtained for the elastic wall one.

scholarly journals Impact of Inflow Boundary Conditions on the Calculation of CT-Based FFR

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 60 ◽  
Author(s):  
Ernest Lo ◽  
Leon Menezes ◽  
Ryo Torii
Keyword(s):  
Boundary Conditions ◽  
Coronary Arteries ◽  
Three Dimensional ◽  
Patient Specific ◽  
Fractional Flow ◽  
Anatomical Models ◽  
Diastolic Phase ◽  
Flow Reserve ◽  
Population Average ◽  
The Impact

Background: Calculation of fractional flow reserve (FFR) using computed tomography (CT)-based 3D anatomical models and computational fluid dynamics (CFD) has become a common method to non-invasively assess the functional severity of atherosclerotic narrowing in coronary arteries. We examined the impact of various inflow boundary conditions on computation of FFR to shed light on the requirements for inflow boundary conditions to ensure model representation. Methods: Three-dimensional anatomical models of coronary arteries for four patients with mild to severe stenosis were reconstructed from CT images. FFR and its commonly-used alternatives were derived using the models and CFD. A combination of four types of inflow boundary conditions (BC) was employed: pulsatile, steady, patient-specific and population average. Results: The maximum difference of FFR between pulsatile and steady inflow conditions was 0.02 (2.4%), approximately at a level similar to a reported uncertainty level of clinical FFR measurement (3–4%). The flow with steady BC appeared to represent well the diastolic phase of pulsatile flow, where FFR is measured. Though the difference between patient-specific and population average BCs affected the flow more, the maximum discrepancy of FFR was 0.07 (8.3%), despite the patient-specific inflow of one patient being nearly twice as the population average. Conclusions: In the patients investigated, the type of inflow boundary condition, especially flow pulsatility, does not have a significant impact on computed FFRs in narrowed coronary arteries.

Numerical Simulation of Electromagnetic Stirring Effect on Flow Pattern of Metal Melt

2011 ◽  
Vol 264-265 ◽  
pp. 1574-1579
Author(s):  
H. Namaki ◽  
S. Hossein Seyedein ◽  
M.R. Afshar Moghadam ◽  
R. Ghasemzadeh
Keyword(s):  
Flow Pattern ◽  
Maxwell Equations ◽  
Flow Model ◽  
Stokes Equations ◽  
Electromagnetic Stirring ◽  
Navier Stokes ◽  
Simultaneous Solution ◽  
Navier Stokes Equations ◽  
Stirring Effect ◽  
Good Agreement

In this study, a mathematical model was developed to simulate 2-D axisymmetric melt flow under magnetic field in a cylindrical container. The modeling of this process required the simultaneous solution of the turbulent Navier-Stokes equations together with Maxwell equations. The flow pattern in liquid bath was obtained using a two-equation κ-є turbulent flow model, which was further used to obtain the solute distribution. The governing differential equations were solved numerically using finite volume based finite difference method. The computed results, were found to be in good agreement with the measurements reported in the literature. The effect of stirring parameters on temperature homogeneity of the melt have been discussed and presented.

Influence of the position of the distal pressure measurement point on the Fractional Flow Reserve using in-silico simulations

2021 ◽  
Author(s):  
Rafael Agujetas ◽  
Conrado Ferrera ◽  
Reyes González-Fernández ◽  
Juan Nogales-Asensio ◽  
Ana Fernández-Tena
Keyword(s):  
Fractional Flow Reserve ◽  
Coronary Stenosis ◽  
Computational Simulation ◽  
Severe Heart Failure ◽  
Invasive Procedure ◽  
Clinical Decision ◽  
Aortic Pressure ◽  
Computed Tomographic Angiography ◽  
Fractional Flow ◽  
Flow Reserve

Abstract Coronary stenosis is largely responsible of severe heart failure as they can stop the blood flow to the myocardial. The Fractional Flow Reserve, the ratio of the mean distal coronary pressure to mean aortic pressure, is the most usual functional assessment of the severity of the coronary stenosis. In most cases, its value dictates the clinical decision to set a stent to restore the flow. Therefore, a correct measurement of this variable is crucial. The objective of this work is to evaluate how the Fractional Flow Reserve value is altered depending on the point where the distal pressure is measured. This information can be very important to prevent cardiologists from making the wrong clinical decisions. From the data taken from anonymous patients who underwent Coronary Computed Tomographic Angiography and cardiac catheterization, a comparison was made with the results of a computational simulation of the model reconstructed from the angiography. The results of the Fractional Flow Reserve obtained by simulation (0.834) agree with those obtained experimentally (0.830), difference less than 0.8%, which indicates that with simulation more results can be obtained than experimentally would be impossible to achieve. The actual invasive procedure to measure the Fractional Flow Reserve is being executed with a protocol that do not consider the influence of the location on the distal pressure value. The new procedure would avoid false results related to the point where the distal pressure is measured.

scholarly journals On the Impact of Fluid Structure Interaction in Blood Flow Simulations

2021 ◽  
Author(s):  
Lukas Failer ◽  
Piotr Minakowski ◽  
Thomas Richter
Keyword(s):  
Blood Flow ◽  
Clinical Importance ◽  
Navier Stokes ◽  
Pressure Amplitude ◽  
Arbitrary Lagrangian Eulerian ◽  
Fractional Flow ◽  
Fluid Structure ◽  
Flow Reserve ◽  
Flow Configurations ◽  
The Impact

AbstractWe study the impact of using fluid-structure interactions (FSI) to simulate blood flow in a stenosed artery. We compare typical flow configurations using Navier–Stokes in a rigid geometry setting to a fully coupled FSI model. The relevance of vascular elasticity is investigated with respect to several questions of clinical importance. Namely, we study the effect of using FSI on the wall shear stress distribution, on the Fractional Flow Reserve and on the damping effect of a stenosis on the pressure amplitude during the pulsatile cycle. The coupled problem is described in a monolithic variational formulation based on Arbitrary Lagrangian Eulerian (ALE) coordinates. For comparison, we perform pure Navier–Stokes simulations on a pre-stressed geometry to give a good matching of both configurations. A series of numerical simulations that cover important hemodynamical factors are presented and discussed.

Comparison of iFR and FFR for coronary physiology evaluation in patients with severe aortic stenosis

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
P Kleczynski ◽  
A Dziewierz ◽  
L Rzeszutko ◽  
D Dudek ◽  
J Legutko
Keyword(s):  
Aortic Stenosis ◽  
Severe Aortic Stenosis ◽  
Complex Nature ◽  
Funding Source ◽  
Fractional Flow ◽  
Science Center ◽  
Roc Curve Analysis ◽  
Coronary Physiology ◽  
Flow Reserve ◽  
Good Agreement

Abstract Background Reliable coronary physiology assessment with pressure derived indexes in patients with aortic stenosis (AS) rises problems due to its complex nature. Recent data suggest that fractional flow reserve (FFR) may underestimate intermediate coronary stenosis in a presence of AS whereas instantaneous wave-free ratio (iFR) values may remain similar after treatment of AS. Furthermore, both indices has not been validated yet in AS. Aim We aimed to find a thresholds for coronary ischemia in the setting of aortic Material and methods The functional significance of 416 coronary lesions was investigated with iFR and FFR measurements in 221 AS patients. The iFR-FFR diagnostic agreement has been tested using the cut-off value for iFR of 0.89. Results Mean value of %DS was 58.6±13.4%, FFR was 0.85±0.07 and iFR – 0.90±0.04. FFR ≤0.80 was measured in 26.0% of interrogated vessels, iFR ≤0.89 – in 33.2%. The correlation between iFR and FFR was good (r=0.83, p<0.001) and with good agreement between iFR and FFR (mean difference −0.0059, 95% CI −0.056–0.062). The AUC at ROC curve analysis for iFR ≤0.89 was 0,997 (0,986 to 1,000, p<0.001) for FFR. According to ROC analysis, the best FFR cut-off in predicting iFR ≤0.89 was ≤0.82 (J=0.96). The diagnostic accuracy for identifying iFR ≤0.89 was 97.7% for FFR. Conclusion In the presence of AS, FFR had good agreement with iFR values. However, FFR threshold for predicting iFR below 0.89 may be different from a standard threshold and that should be taken into account while assessing coronary physiology in the setting of AS. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): National Science Center

scholarly journals Computerised Methodologies for Non-Invasive Angiography-Derived Fractional Flow Reserve Assessment: A Critical Review

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Anantharaman Ramasamy ◽  
Chongying Jin ◽  
Vincenzo Tufaro ◽  
Retesh Bajaj ◽  
Yakup Kilic ◽  
...  
Keyword(s):  
Clinical Practice ◽  
Fractional Flow Reserve ◽  
Navier Stokes ◽  
Fractional Flow ◽  
Navier Stokes Equation ◽  
Non Invasive ◽  
Flow Reserve ◽  
Software Packages ◽  
Coronary Artery Stenoses ◽  
Cumulative Evidence

Fractional flow reserve is the gold standard for assessing the haemodynamic significance of intermediate coronary artery stenoses. Cumulative evidence has shown that FFR-guided revascularisation reduces stent implantations and improves patient outcomes. However, despite the wealth of evidence and guideline recommendations, its use in clinical practice remains minimal. Patient and technical limitations of FFR as well as the need for intracoronary instrumentation, use of adenosine, and increased costs have limited FFR’s applicability in clinical practice. Over the last decade, several angiography-derived FFR software packages have been developed which do not require intracoronary pressure assessment with a guidewire or need for administration of hyperaemic agents. At present, there are 3 commercially available software packages and several other non-commercial technologies that have been described in the literature. These technologies have been validated against invasive FFR showing good accuracy and correlation. However, the methodology behind these solutions is different—some algorithms are based on solving the governing equations of fluid dynamics such as the Navier–Stokes equation while others have opted for a more simplified mathematical formula approach. The aim of this review is to critically appraise the methodology behind all the known angiography-derived FFR technologies highlighting the key differences and limitations.

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