P2433Local blood viscosity and local Reynolds number are associated with coronary plaque calcium and lipid

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
V Thondapu ◽  
E K W Poon ◽  
B Jiang ◽  
M Tacey ◽  
J Dijkstra ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Newtonian Fluid ◽  
Coronary Arteries ◽  
Blood Viscosity ◽  
Fluid Dynamic ◽  
Patient Specific ◽  
Plaque Composition ◽  
Cfd Simulations ◽  
Lower Odds ◽  
Local Reynolds Number

Abstract Background Despite being a shear-thinning non-Newtonian fluid, most computational fluid dynamic (CFD) simulations assume blood to be a Newtonian fluid with constant viscosity. The use of more realistic assumptions may deepen mechanistic understanding of the relationship between blood flow disturbances and atherosclerosis, and improve the diagnostic accuracy of CFD simulations. Purpose To compare associations between plaque composition and local hemodynamics at a single time point using Newtonian versus non-Newtonian rheological models in patient-specific coronary arteries. To investigate whether viscosity-based local haemodynamic indices correlate with plaque composition. Methods Sixteen patient-specific coronary arteries containing non-culprit plaques were reconstructed from optical coherence tomography imaging. CFD simulations using Newtonian and non-Newtonian models were performed to calculate endothelial shear stress (ESS). Local blood viscosity (LBV) and local Reynolds number (ReL) were calculated from non-Newtonian simulation data. Each haemodynamic index was distributed into quintiles, mapped in 5-degree sectors, and compared to plaque composition using logistic regression. Results In total, 69120 sectors from 960 OCT frames were analysed. The lowest ESS quintiles were associated with underlying lipid (ESS<0.8Pa: odds ratio [OR] 1.26, p<0.001, 95% CI 1.15–1.38; ESS 0.8–1.1Pa: OR 1.71, p<0.001, 95% CI 1.58–1.85), while the highest quintile of ESS (>2.2Pa) had lower odds of underlying lipid (OR 0.89, p=0.015, 95% CI 0.82–0.98) compared to the median ESS quintile. However, in the non-Newtonian results, only the second lowest quintile of ESS (1.1–1.5Pa) was associated with lipid (OR 1.54, p<0.001, 95% CI 1.42–1.67). Low ReL was associated with lipid (ReL<28: OR 1.71, p<0.001, 95% CI 1.55–1.89; ReL 28–38: OR 1.47, p<0.001, 95% CI 1.35–1.58). Conversely, the highest quintile of ReL had decreased odds of lipid (ReL>68: OR 0.69, p<0.001, 95% CI 0.62–0.76) (FIGURE). In both the Newtonian and non-Newtonian results, lower ESS was associated with increased odds of underlying calcium. Whereas the lowest quintile of LBV had a lower odds of calcium (LBV<1.4: OR 0.60, p<0.001, 95% CI 0.52–0.71), the highest quintile had significantly higher odds of underlying calcium (LBV>1.5: OR 1.38, p<0.001, 95% CI 1.18–1.63) Conclusions Using the standard Newtonian assumption, low ESS is associated with underlying lipid. However, using a more realistic non-Newtonian rheological model, there is no strong or consistent relationship between ESS and underlying lipid, highlighting the importance of methodological assumptions and lingering questions in arterial CFD simulation. Non-Newtonian indices LBV and ReL are independently associated with calcium and lipid, respectively, suggesting possible mechanistic effects of local blood viscosity in atherosclerosis and implying their use as novel haemodynamic markers of atherosclerosis.

P858High endothelial shear stress and local Reynolds number are associated with lipid growth of coronary plaques

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
V Thondapu ◽  
E K W Poon ◽  
M Tacey ◽  
S Zhu ◽  
J Dijkstra ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Blood Viscosity ◽  
Fluid Dynamic ◽  
Plaque Progression ◽  
Dynamic Simulations ◽  
Rheological Models ◽  
Newtonian Model ◽  
Endothelial Shear Stress ◽  
Local Reynolds Number

Abstract Background Local haemodynamic disturbances in coronary blood flow are associated with abnormal endothelial shear stress (ESS) and progressive atherosclerosis. However, standard techniques to estimate ESS lack the diagnostic specificity necessary for future clinical utility. Possible improvements include use of a more realistic non-Newtonian model of blood, which may provide more accurate ESS measurements and is further able to detect local variations in blood viscosity. Purpose To compare accuracy of ESS generated by Newtonian versus non-Newtonian rheological models to detect coronary plaque progression. To investigate local Reynolds number (ReL), a viscosity-based haemodynamic metric calculated by the non-Newtonian model, as an independent marker of plaque progression. Methods Sixteen patients with non-culprit plaques completely visualised in serial optical coherence tomography (OCT) imaging were identified. Plaques were analysed in 0.2mm intervals at each timepoint for lipid and calcium arc. Computational fluid dynamic simulations were performed using Newtonian and non-Newtonian models to calculate ESS, whereas ReL was calculated by the non-Newtonian simulations. Each haemodynamic index was compared to interval changes in lipid and calcium using multivariate regression. Results In total, 894 matched arterial segments from baseline and follow up imaging were analysed. In the Newtonian results, baseline segments exposed to ESS>1.7Pa had a 12.5° increase in lipid arc (95% CI 2.2° to 22.8°, p=0.018) while segments exposed to ESS<1.1Pa had an 8.1° decrease in calcium (95% CI −14.0° to −2.2°, p=0.007). In the non-Newtonian results, baseline regions exposed to ESS>2.2Pa had a 14.4° increase in lipid (95% CI 4.2° to 24.7°, p=0.006) while areas with ESS<1.4Pa had an 8.7° decrease in calcium (95% CI −14.6° to −2.8°, p=0.004). Baseline regions exposed to ReL<34 showed an average 11.9° increase in lipid arc (95% CI 0.6° to 23.2°, p=0.039). Regions exposed to ReL>55 had an average increase in lipid arc of 26.6° (95% CI 14.5° to 38.6°, p<0.001). Conclusions Both Newtonian and non-Newtonian rheological models show that high ESS is associated with increased lipid while low ESS is associated with decreased calcium. ReL is independently associated with interval increases in lipid arc, suggesting a mechanistic role of local blood viscosity in lipid accumulation. ReL may serve as a novel haemodynamic marker of plaque progression.

P2428Comparison of Newtonian and non-Newtonian rheology in calculation of endothelial shear stress

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
V Thondapu ◽  
E K W Poon ◽  
E Revalor ◽  
S Zhu ◽  
J Dijkstra ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Newtonian Fluid ◽  
Coronary Arteries ◽  
Cardiac Cycle ◽  
Fluid Dynamic ◽  
Patient Specific ◽  
Newtonian Model ◽  
Endothelial Shear Stress ◽  
Point To Point

Abstract Background Although blood is a non-Newtonian fluid, most clinical computational fluid dynamic (CFD) studies assume blood to be a Newtonian fluid with constant viscosity. At higher blood flow rates in larger arteries, the two models should present similar results, and the Newtonian assumption can be considered acceptable. However, whether the Newtonian assumption is valid in patient-specific coronary arteries under pulsatile flow has not been evaluated. Purpose To compare CFD results using Newtonian and non-Newtonian models of blood in order to determine whether the Newtonian assumption can be considered valid in patient-specific coronary arteries. Methods Coronary arteries of 16 patients were reconstructed from fusion of angiography and intracoronary optical coherence tomography imaging. Pulsatile CFD simulations using Newtonian and non-Newtonian models were performed to calculate endothelial shear stress (ESS). The absolute and percent difference in time-averaged and instantaneous ESS values (calculated as non-Newtonian minus Newtonian) were compared on a point-to-point basis. The percent area of the vessel exposed to proatherogenic ESS values (considered <1 Pa) in each model was also calculated. Results The Newtonian and non-Newtonian models produce similar qualitative distributions of ESS. However, quantitative comparison shows that compared to the Newtonian results, the non-Newtonian model estimates significantly higher time-averaged ESS (2.04±0.63Pa versus 1.59±0.54Pa, 95% CI 0.39–0.49, p<0.001) throughout the cardiac cycle. This results in significantly greater estimate of area exposed to ESS <1Pa in the Newtonian model (50.43±14.16% versus 37.20±13.57%, 95% CI 11.28–15.18, p<0.001). Instantaneous ESS plotted through the cardiac cycle indicates the greatest divergence in ESS values occurs at the transition between end-systole and early diastole, at approximately 0.35 seconds (FIGURE). Conclusions Despite similar qualitative ESS distributions, Newtonian and non-Newtonian simulations provide significantly different quantitative ESS values. This suggests that in patient-specific simulations of coronary blood flow, the non-Newtonian model may increase accuracy of ESS measurements. We hypothesize that using a non-Newtonian model may improve the diagnostic accuracy of abnormal ESS to predict clinically significant progression of atherosclerosis, however further study is necessary.

Patient-Specific Stented Coronary Bifurcations: Numerical Analysis of Near-Wall Quantities and the Bulk Flow

2013 ◽  
Author(s):  
Claudio Chiastra ◽  
Stefano Morlacchi ◽  
Diego Gallo ◽  
Umberto Morbiducci ◽  
Rubén Cárdenes ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Shear Stress ◽  
Coronary Arteries ◽  
Fluid Dynamic ◽  
Patient Specific ◽  
Wall Region ◽  
Stent Restenosis ◽  
Local Measurements ◽  
In Stent Restenosis

The mechanisms and the causes of the in-stent restenosis process in coronary arteries are not fully understood. One of the most relevant phenomena, which seems to be associated to this process, is an altered hemodynamics in the stented wall region [1]. In vivo local measurements of velocities and their gradients in human coronary arteries are very difficult and can hardly be applied to successfully investigate the fluid dynamic field [1]. Alternatively, virtual models of blood flow in patient-specific coronary arteries allow the study of local fluid dynamics and the computation of the wall shear stress (WSS) and other quantities which can be related to the risk of restenosis.

Estimation of endothelial shear stress in atherosclerotic lesions detected by intravascular ultrasound using computational fluid dynamics from coronary CT scans with a pulsatile blood flow and an individualized blood viscosity

2021 ◽  
pp. 1-14
Author(s):  
Adrian Curta ◽  
Ahmad Jaber ◽  
Johannes Rieber ◽  
Holger Hetterich
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Shear Stress ◽  
Coronary Arteries ◽  
Blood Viscosity ◽  
Flow Profile ◽  
Cfd Simulations ◽  
Coronary Ct ◽  
Endothelial Shear Stress

INTRODUCTION: Endothelial shear stress (ESS) is a local hemodynamic factor that is dependent on vessel geometry and influences the process of atherogenesis. As in vivo measurements of ESS are not possible, it must be calculated using computational fluid dynamics (CFD). In this feasibility study we explore CFD-models generated from coronary CT-angiography (CCTA) using an individualised blood viscosity and a pulsatile flow profile derived from in vivo measurements. MATERIALS AND METHODS: We retrospectively recruited 25 consecutive patients who received a CCTA followed by a coronary angiography including intravascular ultrasound (IVUS) and generated 3D models of the coronary arteries from the CT-datasets. We then performed CFD-simulations on these models. Hemodynamically non-relevant stenosis were identified in IVUS. They were isolated in the CFD-model and separated longitudinally into a half with atherosclerotic lesion (AL) and one without (NAL). ESS was measured and compared for both halves. RESULTS: After excluding vessels with no IVUS data or relevant stenosis we isolated 31 hemodynamically non-relevant excentric AL from a total of 14 vessels. AL segments showed consistently significantly lower ESS when compared to their corresponding NAL segments when regarding minimum (0.9 Pa, CI [0.6, 1.2] vs. 1.3 Pa, CI [0.9, 1.8]; p = 0.004), mean (5.0 Pa, CI [3.4, 6.0] vs. 6.7 Pa, CI [5.5, 8.4]; p = 0.008) and maximum ESS values (12.4 Pa, CI [8.6, 14.6] vs. 19.6 Pa, CI [12.4, 21.0]; p = 0.005). Qualitatively ESS was lower on the inside of bifurcations and curvatures. CONCLUSION: CFD simulations of coronary arteries from CCTA with an individualised flow profile and blood viscosity are feasible and could provide further prognostic information and a better risk stratification in coronary artery disease. Further prospective studies are needed to investigate this claim.

scholarly journals Computational fluid dynamic simulations of image-based stented coronary bifurcation models

2013 ◽  
Vol 10 (84) ◽  
pp. 20130193 ◽  
Author(s):  
Claudio Chiastra ◽  
Stefano Morlacchi ◽  
Diego Gallo ◽  
Umberto Morbiducci ◽  
Rubén Cárdenes ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Coronary Arteries ◽  
Fluid Dynamic ◽  
Patient Specific ◽  
Conventional Coronary Angiography ◽  
Coronary Bifurcation ◽  
Dynamic Simulations ◽  
Stent Restenosis ◽  
Relative Residence Time ◽  
In Stent Restenosis

One of the relevant phenomenon associated with in-stent restenosis in coronary arteries is an altered haemodynamics in the stented region. Computational fluid dynamics (CFD) offers the possibility to investigate the haemodynamics at a level of detail not always accessible within experimental techniques. CFD can quantify and correlate the local haemodynamics structures which might lead to in-stent restenosis. The aim of this work is to study the fluid dynamics of realistic stented coronary artery models which replicate the complete clinical procedure of stent implantation. Two cases of pathologic left anterior descending coronary arteries with their bifurcations are reconstructed from computed tomography angiography and conventional coronary angiography images. Results of wall shear stress and relative residence time show that the wall regions more prone to the risk of restenosis are located next to stent struts, to the bifurcations and to the stent overlapping zone for both investigated cases. Considering a bulk flow analysis, helical flow structures are generated by the curvature of the zone upstream from the stent and by the bifurcation regions. Helical recirculating microstructures are also visible downstream from the stent struts. This study demonstrates the feasibility to virtually investigate the haemodynamics of patient-specific coronary bifurcation geometries.

Steady Versus Pulsatile Flow Modeling for Hemodynamics Based Stratification of a Population of Intracranial Aneurysms

2011 ◽  
Author(s):  
Rohini Retarekar ◽  
Benjamin Berkowitz ◽  
Madhavan L. Raghavan
Keyword(s):  
Pulsatile Flow ◽  
Intracranial Aneurysms ◽  
Fluid Dynamic ◽  
Temporal Variations ◽  
Patient Specific ◽  
Depth Information ◽  
Specific Information ◽  
Cfd Simulations ◽  
Flow Simulations ◽  
Anatomical Information

Hemodynamics is thought to play a role in the initiation and subsequent growth of intracranial aneurysms. Hemodynamics of an aneurysm is strongly related to its underlying morphology, specifically, the size and shape of the aneurysm sac and its contiguous vasculature [1]. Although the Computational Fluid Dynamic (CFD) simulations of transient blood flow seemingly provide in depth information of intra-aneurysmal hemodynamics, the simulations are often computationally expensive and demand additional measurements or assumptions such as the temporal variations in boundary conditions. When a population of aneurysms, with distinct sizes and shapes, are being studied in order to stratify them according to hemodynamics, it is conceivable that steady flow simulations are as effective as pulsatile flow simulations, especially when anatomical information is the only patient-specific information available. The objective of this study is to compare steady versus pulsatile flow simulations for a controlled hypothetical population of aneurysms with realistic variation in sac morphology and contiguous vasculature.

Abstract 15117: The Catheter Uncertainty Principle: Does the Presence of a Catheter Alter Hemodynamics?

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Michael Kaplan ◽  
Madhurima Vardhan ◽  
Amanda RANDLES
Keyword(s):  
Coronary Arteries ◽  
Lattice Boltzmann ◽  
Clinical Decision Making ◽  
Pressure Field ◽  
Fluid Dynamic ◽  
Diagnostic Procedures ◽  
Clinical Decision ◽  
Patient Specific ◽  
Dynamic Simulations ◽  
Catheter Size

Introduction: Catheters are an essential component of measuring invasive hemodynamic quantities. However, by the very nature of a catheter's presence, it acts to disturb the normal flow field, potentially altering measured pressures and derived quantities, such as FFR. Computational fluid dynamic simulations are performed to explore how vessel lumenal area and catheter size effect pressures. Methods: Patient-specific anatomical reconstructions are coupled with HARVEY, a massively parallel lattice-Boltzmann fluid solver, to calculate 3D blood flow around simulated catheters. We explore the effects of catheter size in vessels ranging from 5 mm in diameter, a right ventricle to pulmonary artery shunt (RVPAS) in a patient with HLHS, and smaller, in coronary arteries. Pressures sampled at the location corresponding to the distal end of the catheter are compared and FFR is calculated for the coronary models. Results: Figure 1A illustrates the calculated pressure waveforms for simulated catheter sizes in a RVPAS. In this case, the catheter does not significantly alter the pressure field unless unrealistically large catheters, such as a 13 Fr, are used. For adult coronary arteries (Figure 1B), reasonable catheter sizes result in appreciable decreases in sampled pressures and, consequently, in calculated FFR (Figure 1C). Conclusion: The presence of a sufficiently large catheter (>50% of the vessel lumenal area) causes a noticeable decrease in the pressures at the tip of the catheter. While unlikely to occur in larger vessels, this can occur during left heart catheterizations of diseased coronary arteries. This causes an artificial decrease in FFR, which can potentially alter clinical decision making. While catheters are the gold standard for pressure measurements, an improved understanding of the inherent sensitivity of their measurements to unobstructed vessel lumenal area is important for interpreting the results of catheter-based diagnostic procedures.

scholarly journals Hemodynamic Abnormalities in the Aorta of Turner Syndrome Girls

2021 ◽  
Vol 8 ◽  
Author(s):  
Lauren Johnston ◽  
Ruth Allen ◽  
Pauline Hall Barrientos ◽  
Avril Mason ◽  
Asimina Kazakidi
Keyword(s):  
Shear Stress ◽  
Turner Syndrome ◽  
Fluid Dynamic ◽  
Vortical Flow ◽  
Patient Specific ◽  
Cfd Simulations ◽  
Heterogeneous Distribution ◽  
Relative Residence Time ◽  
Increased Risk ◽  
Homogeneous Pattern

Congenital abnormalities in girls and women with Turner syndrome (TS), alongside an underlying predisposition to obesity and hypertension, contribute to an increased risk of cardiovascular disease and ultimately reduced life expectancy. We observe that children with TS present a greater variance in aortic arch morphology than their healthy counterparts, and hypothesize that their hemodynamics is also different. In this study, computational fluid dynamic (CFD) simulations were performed for four TS girls, and three age-matched healthy girls, using patient-specific inlet boundary conditions, obtained from phase-contrast MRI data. The visualization of multidirectional blood flow revealed an increase in vortical flow in the arch, supra-aortic vessels, and descending aorta, and a correlation between the presence of aortic abnormalities and disturbed flow. Compared to the relatively homogeneous pattern of time-averaged wall shear stress (TAWSS) on the healthy aortae, a highly heterogeneous distribution with elevated TAWSS values was observed in the TS geometries. Visualization of further shear stress parameters, such as oscillatory shear index (OSI), normalized relative residence time (RRTn), and transverse WSS (transWSS), revealed dissimilar heterogeneity in the oscillatory and multidirectional nature of the aortic flow. Taking into account the young age of our TS cohort (average age 13 ± 2 years) and their obesity level (75% were obese or overweight), which is believed to accelerate the initiation and progression of endothelial dysfunction, these findings may be an indication of atherosclerotic disease manifesting earlier in life in TS patients. Age, obesity and aortic morphology may, therefore, play a key role in assessing cardiovascular risk in TS children.

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