Wall Shear Stress Patterns Research Articles

The influence of strut-connectors in coronary stents: A comparison of numerical simulations and μPIV measurements

Abstract This paper discusses the influence of different designs of strut-connectors of stents by numerical flow simulations and flow examinations using micro particle image velocimetry (μPIV). Many studies have shown that there is a correlation between the hemodynamics after stent implantation and the cause of biological responses like thrombosis and the in-stent restenosis. Recirculation areas may occur through a stent, which are considered to be the cause of these clinical complications. In this study, three different coronary stent designs are investigated and the hemodynamic effects from the different designs is presented. The study focuses on the design of the strut-connectors that connect two struts. Numerical simulations were performed to evaluate various flow features like recirculation zones, velocity profiles and wall shear stress (WSS) patterns. To verify the numerical results μPIVmeasurements were performed. It could be shown that the alignment in the main stream of the connectors influences the size and number of recirculation zones.

Influence of Artery Straightening on Local Hemodynamics in Left Anterior Descending (LAD) Artery after Stent Implantation.

Objectives The study investigates local hemodynamic environment changes caused by straightening phenomenon and the relationship between straightening phenomenon and in-stent restenosis. Background Intravascular intervention is an effective treatment in restoring the normal flow conditions and vascular lumen. Unfortunately, in-stent restenosis often occurs in a subset of patients after stent implantation and limits the success of stent implantation outcomes. The implanted stent usually causes artery straightening locally, rather than coinciding and adjusting to the physiological curve exactly. Artery straightening would apparently modify the artery geometry and therefore alter the local hemodynamic environment, which may result in intimal hyperplasia and restenosis after stenting implantation. Methods In the current investigation, we verify the hypothesis that the artery straightening influences the local hemodynamic state using the different 3D CT models. Flow analysis for blood in the left anterior descending coronary artery and the straightening model is simulated numerically. Result The current results reveal that the straightening phenomenon alters the distribution of wall shear stress and flow patterns, decreases the wall shear stress (WSS), and increases the oscillatory shear index (OSI) and the relative residence time (RRT), especially at the proximal and distal areas of stenting. Conclusions The local straightened geometry established after stent implantation was likely to generate portions of the stenting area to a high risk of neointimal hyperplasia and subsequent restenosis.

Law-of-the-wall analytical formulations for Type-A turbulent boundary layers

In-depth analyses of existing direct numerical simulations (DNS) data led to a logical and important classification of generic turbulent boundary layers (TBLs), namely Type-A, -B and -C TBL, based on the distribution patterns of the time-averaged wall-shear stress. Among these types, Type-A TBL and its related law formulations were investigated in terms of the analytical velocity profiles independent on Reynolds number (Re). These formulations were benchmarked by the DNS data of turbulence on a zero-pressure-gradient flat-plate (ZPGFP). With reference to the analysis from von Karman in developing the traditional law-of-the-wall, the current study first physically distinguished the time-averaged local scale used by von Karman from the time-space-averaged scale defined in the current paper, and then derived the governing equations with the Re — independency under the time-space-averaged scales. Based on the indicator function (IDF) and TBL thickness, the sublayer partitions were quantitatively defined. The analytical formulations for entire ZPGFP TBL were derived, including the formula in the inner, buffer, semi-logarithmic (semi-log) and wake layers. The research profoundly understood the damping phenomenon and its controlling mechanism in the TBL with its associated mathematical expressions, namely the damping function under both linear and logarithmic coordinates. Based on these understandings and the quantified TBL partitions, the analytical formulations for the entire ZPGFP TBL were established and were further proved being uniform and consistent under both the time-averaged local and the time-space-averaged scales. Comparing to the traditional law, these formulations were validated by the existing DNS data with more accuracy and wider applicability. The findings advance the current understandings of the conventional TBL theory and its well-known foundation of law-of-the-wall.

Hemodynamic and Histopathological Changes in the Early Phase of the Development of an Intracranial Aneurysm.

Hemodynamic stress and chronic inflammation are closely associated with the pathogenesis of intracranial aneurysms (IAs). However, the hemodynamic and biological mechanisms triggering IA formation remain to be elucidated. To clarify them, computational fluid dynamics (CFD) and histopathological analyses in the early phase of IA development using an experimentally induced IA model in rats were conducted. Histological changes in the early phase of IA development were observed under a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Using data from 7-T magnetic resonance angiography (7T-MRA), CFD analyses were performed to determine wall shear stress (WSS) and wall pressure (WP) at the prospective site of IA. A bump-like protrusion named an “intimal pad” was located in the anterior cerebral artery (ACA) immediately distal to the apex of the bifurcation. TEM showed the degeneration of the internal elastic lamina (IEL) and longitudinally elongated smooth muscle cells (SMCs) that switched from the contractile to the proliferative phenotype and penetrated between two divided layers of the degenerated IEL in the prospective site of the IA. However, no inflammatory cells were observed. CFD analyses showed no particular pattern of WSS and WP at the prospective IA site. IEL degeneration and the phenotypic change and longitudinal elongation of SMCs were identified as the early events in IA development. CFD analyses and TEM data suggest that these biological events may be derived from increased circumferential wall stress due to increased blood pressure and increased longitudinal wall strain due to the existence of the intimal pad.

Optimal Site for Proximal Optimization Technique in Complex Coronary Bifurcation Stenting: A Computational Fluid Dynamics Study

Background/purposeThe optimal position of the balloon distal radio-opaque marker during the post optimization technique (POT) remains debated. We analyzed three potential different balloon positions for the final POT in two different two-stenting techniques, to compare the hemodynamic effects in terms of wall shear stress (WSS) in patients with complex left main (LM) coronary bifurcation. Methods/materialsWe reconstructed the patient-specific coronary bifurcation anatomy using the coronary computed tomography angiography (CCTA) data of 8 consecutive patients (6 males, mean age 68.2± 18.6 years) affected by complex LM bifurcation disease. Subsequently a virtual bench test was performed in each patient using two different double stenting techniques represented by the DK and Nano crush using the reconstruction of Orsiro stents (Biotronik IC, Bulack, Switzerland). ResultsA significant reduction in the mean WSS values in all the lesion's sites was observed when the final POT was performed 1 mm distally the carina cut plane in both techniques. Moreover, a significant improvement in the mean WSS values of the entire SB (e.g. LCX) was obtained performing the POT 1 mm distally to the carina cut plane. The proximal POT resulted in larger area of lower WSS values at the carina using both the Nano crush and the DK crush techniques. ConclusionsIn patients with complex LM bifurcation disease the use of a final POT performed 1 mm distally to the carina cut plane might results in more favorable WSS patterns (i.e. higher WSS values) along all stented segments and, especially, along the entire LCX lesions.

In-exercise vascular shear rate during acute continuous and interval exercise: impact on endothelial function and miR-21.

Endothelial cell phenotype and endothelial function are regulated by hemodynamic forces, particularly wall shear stress (WSS). During a single bout of exercise, the specific exercise protocol can affect in-exercise WSS patterns and, consequently, endothelial function. MicroRNAs might provide a biomarker of in-exercise WSS pattern to indicate whether a specific exercise bout will have a positive effect on endothelial function. We evaluated the effect of acute interval (IT) and continuous (CON) in-exercise WSS patterns upon postexercise endothelial function and circulating microRNA (miR)-21 expression. Methods and results: 13 participants performed CON and 3 different IT exercise protocols matched for duration and intensity on separate days. Oxygen uptake, heart rate, and brachial artery blood flow were recorded throughout the exercise. Brachial artery flow-mediated dilation (FMD) was performed pre-exercise and 15 min postexercise. Plasma samples were acquired pre-exercise and 6 h postexercise to determine miR-21 expression. In-exercise shear rate (SR) patterns (a surrogate of WSS) differed according to the CON or IT work-rate profile. In-exercise anterograde SR was greater in CON than IT exercise (P < 0.05), but retrograde SR was equivalent between exercise protocols (P > 0.05). Oscillatory shear index was higher during IT versus CON exercise (P < 0.05). Postexercise FMD increased (pre: 7.08% ± 2.95%, post: 10.54% ± 4.24%, P < 0.05), whereas miR-21 expression was unchanged (pre: 12.0% ± 20.7% cel-miR-39, post: 11.1 ± 19.3% cel-miR-39, P > 0.05) with no effect of exercise protocol (P > 0.05). Conclusions: CON and IT exercise induced different SR patterns but equivalent improvements in acute endothelial function. The absence of change in miR-21 expression suggests that miR-21 is not a suitable biomarker of exercise-induced SR.NEW & NOTEWORTHY Interval exercise has the potential to negatively impact vascular adaptations because of repeated oscillations in vascular shear. To our knowledge, we are the first to continuously assess exercise-induced shear throughout different acute exercise protocols and examine its relationship with acute endothelial function and a circulating biomarker of shear (miR-21). These experiments provide clear data indicating enhancement of the acute vascular response from differing interval exercise protocols, with the study also providing detailed vascular and shear responses for future reference.

4D modelling of fluid mechanics in the zebrafish embryonic heart.

Abnormal blood flow mechanics can result in pathological heart malformation, underlining the importance of understanding embryonic cardiac fluid mechanics. In the current study, we performed image-based computational fluid dynamics simulation of the zebrafish embryonic heart ventricles and characterized flow mechanics, organ dynamics, and energy dynamics in detail. 4D scans of 5days post-fertilization embryonic hearts with GFP-labelled myocardium were acquired using line-scan focal modulation microscopy. This revealed that the zebrafish hearts exhibited a wave-like contractile/relaxation motion from the inlet to the outlet during both systole and diastole, which we showed to be an energy efficient configuration. No impedance pumping effects of pressure and velocity waves were observed. Due to its tube-like configuration, inflow velocities were higher near the inlet and smaller at the outlet and vice versa for outflow velocities. This resulted in an interesting spatial wall shear stress (WSS) pattern where WSS waveforms near the inlet and those near the outlet were out of phase. There was large spatial variability in WSS magnitudes. Peak WSS was in the range of 47.5-130dyne/cm2 at the inflow and outflow tracts, but were much smaller, in the range of 4-11dyne/cm2, in the mid-ventricular segment. Due to very low Reynolds number and the highly viscous environment, intraventricular pressure gradients were high, suggesting substantial energy losses of flow through the heart.

The influence of flow asymmetry on refractory erosion in the vacuum chamber of a RH degasser

Nozzle blockage in RH reactors is a serious operational problem since it can cause an asymmetric distribution of the steel flow in both the up-leg as well as the lower region of the vacuum chamber. This anomaly can alter the circulation rate in addition to affecting the erosion profile of the lower part of vacuum chamber refractory lining. In this study, the effect of nozzle obstruction on liquid circulation rate, wall shear stress, velocity profiles and flow pattern have been evaluated. In addition, refractory erosion in the vacuum chamber has been estimated through physical modeling and mathematical simulation results. Four blockage conditions were studied for different gas flow rates. There was a good agreement in physical and mathematical models results. Asymmetric flow was observed in vacuum chamber lower region in asymmetric blockage cases, which resulted in preferential wear on one chamber side in physical modeling experiments. The wall shear stress analysis in the vacuum chamber using a fluid dynamic model also indicates preferential erosion. When compared, refractory erosion results in physical modeling and shear stress in mathematical modeling presented good correlation.

Measurements of the wall-shear stress distribution in turbulent channel flow using the micro-pillar shear stress sensor MPS3

This study investigates the wall-shear stress (WSS) distribution in turbulent channel flow at friction Reynolds numbers of Reτ=860 and 1300 using the micro-pillar shear-stress sensor (MPS3). The probability density functions and the joint probability density functions of the wall-shear stress vectors indicate that the intermittency of the flow increases for higher Reynolds numbers. Extreme events occurring at the wall, such as wall-normal velocity spikes and backflow events, are detected and analyzed based on the wall-shear stress patterns. The events representing the wall-normal spikes are conditionally sampled from the wall-normal velocity component, which is determined from the local wall-shear stress gradients. The results show that the negative velocity spikes tend to co-occur with strong streamwise wall-shear stress motions, and that the positive spikes are likely to accompany large spanwise motions. Rare backflow events are detected from the wall-shear stressdistribution for both Reynolds numbers, serving as an experimental evidence of near-wall flow reversal events in turbulent channel flow. The diameter of the detected backflow region is approximately 20 viscous units. The data confirm the results from previous numerical studies. The wall-normal velocity spikes and the backflow events are likely to be three-dimensional, suggesting an energy and momentum transfer between the viscous sublayer and the outer part of the turbulent channel flow.

Bileaflet Mechanical Aortic Valve Prosthesis Orientation Influences Ascending Aortic Blood Flow Patterns

Objective: In analogue to bicuspid aortic valves, bileaflet mechanical heart valves (BMHV) implanted in aortic position may influence blood flow and wall shear stress (WSS) patterns in the ascendin...

Bileaflet mechanical aortic valves do not alter ascending aortic wall shear stress

Progressive ascending aortic dilatation has been observed after mechanical aortic valve replacement (mAVR), possibly due to altered blood flow and wall shear stress (WSS) patterns induced by their bileaflet design. We examined the effect of mAVR on WSS in the ascending aorta using time-resolved 4D flow MRI. Fifteen patients with mechanical aortic valve prostheses, 10 patients with bicuspid aortic valve disease and 10 healthy individuals underwent thoracic 4D flow MRI. Peak systolic hemodynamic parameters (velocity and WSS) and vessel diameters were assessed in the ascending aorta. In addition, three-dimensional per-voxel analysis was used to compare velocity and WSS between patient groups and healthy controls. Peak aortic diameters were significantly higher in mAVR and BAV patients compared to healthy controls (p = 0.011). Mean aortic diameters were comparable between mAVR and BAV patients. No differences in 4D flow MRI-derived mean blood flow velocity and peak WSS were found between the three groups. Compared to healthy controls, mean WSS was significantly lower in mAVR patients (p = 0.031). Per-voxel analysis revealed no increased WSS in the ascending aortic wall and significantly lower velocity and WSS values in mAVR patients compared to healthy controls. In contrast, regions of significantly increased outer lumen velocities and WSS in BAV patients compared to healthy controls were found. This study shows that there is no increased ascending aortic WSS after mAVR. Our results suggest that, in contrast to BAV patients, there is no indication for intensified follow-up of the ascending aorta after mAVR.

Abstract WMP33: Towards Cerebral Aneurysm Rupture Risk Prediction Using Quantitative Analysis by 4D Flow MRI: Intra-Aneurysmal Vortical Blood Flow and Association to Wall Shear Stress

Introduction: While previous studies have shown a link between changes in aneurysmal wall shear stress (WSS) and risk of rupture, the association between the development of WSS variations and intra-aneurysmal hemodynamic flow patterns remain unknown. Understanding such link could potentially lead to novel early biomarkers for risk stratification of aneurysmal rupture. Aim: To assess the association between intra-aneurysmal flow patterns behavior and WSS in cerebral aneurysm patients. Methods: Time-resolved 3D blood flow velocities were acquired by dual-venc 4D flow MRI (kt-GRAPPA R=5, voxel size (1.0x 1.0 x 1.0 mm 3 ), TE/TR 3.5/6.2 ms, temporal resolution 57ms, venc low /venc high 50/100 cm/s) in 12 patients (66 ± 9 years, 8 F), who presented with a total of 14 cerebral aneurysms (average 10-time points per aneurysm synchronized with the cardiac cycle). Time-resolved median WSS was quantified over the 3D aneurysm surface. To quantify 3D blood flow pattern behavior from 4D Flow MRI, we used the fluid dynamics-based helicity metric. Helicity is a signed quantity that measures the strength and alignment between vortical pattern and blood flow directions. Helicity magnitudes take positive values at regions where both vortical pattern and blood flow align in the same direction while regions with opposing directions have negative values. Time-resolved positive and negative helicity were quantified separately by instantaneous volumetric median and correlated with WSS. Correlation was tested using pooled paired data of all acquired time points from all aneurysms (N=147 samples). Results: (Fig.1) Strong correlations were found between WSS and flow patterns behavior with the strongest correlation (R=0.91, p&lt;0.001) found with negative helicity. Conclusions: We revealed that intra-aneurismal blood flow pattern behavior strongly correlates with wall shear stress. These results may help in the future to identify early hemodynamic markers for risk of aneurysmal rupture.

Asymmetry in Mechanosensitive Gene Expression during Aortic Arch Morphogenesis

Embryonic aortic arches (AA) are initially bilaterally paired, transitional vessels and failures in remodeling based on hemodynamic and growth-related adaptations cause a spectrum of congenital heart disease (CHD) anatomies. Identifying regulatory mechanisms and cross-talk between the genetic elements of these vessels are critical to understand the ethiology of CHD and refine predictive computational models. This study aims to screen expression profiles of fundamental biological pathways in AA at early stages of chick embryo morphogenesis and correlate them with our current understanding of growth and mechanical loading. Reverse transcription-quantitative PCR (RT-qPCR) was followed by correlation and novel peak expression analyses to compare the behaviour and activation period of the genes. Available protein networks were also integrated to investigate the interactions between molecules and highlight major hierarchies. Only wall shear stress (WSS) and growth-correlated expression patterns were investigated. Effect of WSS was seen directly on angiogenesis as well on structural and apoptosis-related genes. Our time-resolved network suggested that WSS-correlated genes coordinate the activity of critical growth factors. Moreover, differential gene expression of left and right AA might be an indicator of subsequent asymmetric morphogenesis. These findings may further our understanding of the complex processes of cardiac morphogenesis and errors resulting in CHD.

Wall Shear Stress and Flow Patterns in Unruptured and Ruptured Anterior Communicating Artery Aneurysms Using Computational Fluid Dynamics.

ObjectiveThe goal of this study was to compare several parameters, including wall shear stress (WSS) and flow pattern, between unruptured and ruptured anterior communicating artery (ACoA) aneurysms using patient-specific aneurysm geometry. MethodsIn total, 18 unruptured and 24 ruptured aneurysms were analyzed using computational fluid dynamics (CFD) models. Minimal, average, and maximal wall shear stress were calculated based on CFD simulations. Aneurysm height, ostium diameter, aspect ratio, and area of aneurysm were measured. Aneurysms were classified according to flow complexity (simple or complex) and inflow jet (concentrated or diffused). Statistical analyses were performed to ascertain differences between the aneurysm groups. ResultsAverage wall shear stress of the ruptured group was greater than that of the unruptured group (9.42% for aneurysm and 10.38% for ostium). The average area of ruptured aneurysms was 31.22% larger than unruptured aneurysms. Simple flow was observed in 14 of 18 (78%) unruptured aneurysms, while all ruptured aneurysms had complex flow (p<0.001). Ruptured aneurysms were more likely to have a concentrated inflow jet (63%), while unruptured aneurysms predominantly had a diffused inflow jet (83%, p=0.004). ConclusionRuptured aneurysms tended to have a larger geometric size and greater WSS compared to unruptured aneurysms, but the difference was not statistically significant. Flow complexity and inflow jet were significantly different between unruptured and ruptured ACoA aneurysms.

Transcatheter aortic valve replacement alters ascending aortic blood flow and wall shear stress patterns: A 4D flow MRI comparison with age-matched, elderly controls

BackgroundWith the implementation of transcatheter aortic valve replacement (TAVR) in lower-risk patients, evaluation of blood flow characteristics and the effect of TAVR on aortic dilatation becomes of considerable interest. We employed 4D flow MRI in the ascending aorta of patients after TAVR to assess wall shear stress (WSS) and compare blood flow patterns with surgical aortic valve replacement (SAVR) and age- and gender-matched controls.MethodsFourteen post-TAVR patients and ten age- and gender-matched controls underwent kt-PCA accelerated 4D flow MRI of the thoracic aorta at 3.0 Tesla. Velocity and wall shear stress was compared between the two groups. In addition, aortic flow eccentricity and displacement was assessed and compared between TAVR patients, controls and 14 SAVR patients recruited as part of an earlier study.ResultsCompared to controls, abnormally elevated WSS was present in 30±10% of the ascending aortic wall in TAVR patients. Increased WSS was present along the posterior mid-ascending aorta and the anterior distal-ascending aorta in all TAVR patients. TAVR results in eccentric and displaced flow in the mid- and distal-ascending aorta, whereas blood flow displacement in SAVR patients occurs only in the distal-ascending aorta.ConclusionThis study shows that TAVR results in increased blood flow velocity and WSS in the ascending aorta compared to age- and gender-matched elderly controls. This finding warrants longitudinal assessment of aortic dilatation after TAVR in the era of potential TAVR in lower-risk patients. Additionally, TAVR results in altered blood flow eccentricity and displacement in the mid- and distal-ascending aorta, whereas SAVR only results in altered blood flow eccentricity and displacement in the distal-ascending aorta.Key Points• TAVR results in increased blood flow velocity and WSS in the ascending aorta.• Longitudinal assessment of aortic dilatation after TAVR is warranted in the era of potential TAVR in lower-risk patients.• Both TAVR and SAVR result in altered blood flow patterns in the ascending aorta when compared to age-matched controls.

Re-understanding the law-of-the-wall for wall-bounded turbulence based on in-depth investigation of DNS data

Based on direct numerical simulation (DNS) data of the straight ducts, namely square and rectangular annular ducts, detailed analyses were conducted for the mean streamwise velocity, relevant velocity scales, and turbulence statistics. It is concluded that turbulent boundary layers (TBL) should be broadly classified into three types (Type-A, -B, and -C) in terms of their distribution patterns of the time-averaged local wall-shear stress ( $$\tau _\mathrm{w} )$$ or the mean local frictional velocity ( $$u_\tau )$$ . With reference to the Type-A TBL analysis by von Karman in developing the law-of-the-wall using the time-averaged local frictional velocity ( $$u_\tau )$$ as scale, the current study extended the approach to the Type-B TBL and obtained the analytical expressions for streamwise velocity in the inner-layer using ensemble-averaged frictional velocity ( $$\bar{{u}}_\tau )$$ as scale. These analytical formulae were formed by introducing the general damping and enhancing functions. Further, the research applied a near-wall DNS-guided integration to the governing equations of Type-B TBL and quantitatively proved the correctness and accuracy of the inner-layer analytical expressions for this type.

Flow-Structure Interaction Simulations of the Aortic Heart Valve at Physiologic Conditions: The Role of Tissue Constitutive Model.

The blood flow patterns in the region around the aortic valve depend on the geometry of the aorta and on the complex flow-structure interaction between the pulsatile flow and the valve leaflets. Consequently, the flow depends strongly on the constitutive properties of the tissue, which can be expected to vary between healthy and diseased heart valves or native and prosthetic valves. The main goal of this work is to qualitatively demonstrate that the choice of the constitutive model of the aortic valve is critical in analysis of heart hemodynamics. To accomplish that two different constitutive models were used in curvilinear immersed boundary-finite element-fluid-structure interaction (CURVIB-FE-FSI) method developed by Gilmanov et al. (2015, "A Numerical Approach for Simulating Fluid Structure Interaction of Flexible Thin Shells Undergoing Arbitrarily Large Deformations in Complex Domains," J. Comput. Phys., 300, pp. 814-843.) to simulate an aortic valve in an anatomic aorta at physiologic conditions. The two constitutive models are: (1) the Saint-Venant (StV) model and (2) the modified May-Newman&Yin (MNY) model. The MNY model is more general and includes nonlinear, anisotropic effects. It is appropriate to model the behavior of both prosthetic and biological tissue including native valves. Both models are employed to carry out FSI simulations of the same valve in the same aorta anatomy. The computed results reveal dramatic differences in both the vorticity dynamics in the aortic sinus and the wall shear-stress patterns on the aortic valve leaflets and underscore the importance of tissue constitutive models for clinically relevant simulations of aortic valves.

Perioperative evaluation of regional aortic wall shear stress patterns in patients undergoing aortic valve and/or proximal thoracic aortic replacement

ObjectivesTo assess in patients with aortopathy perioperative changes in thoracic aortic wall shear stress (WSS), which is known to affect arterial remodeling, and the effects of specific surgical interventions. MethodsPresurgical and postsurgical aortic 4D flow MRI were performed in 33 patients with aortopathy (54 ± 14 years; 5 women; sinus of Valsalva (d_SOV)/midascending aortic (d_MAA) diameters = 44 ± 5/45 ± 6 mm) scheduled for aortic valve (AVR) and/or root (ARR) replacement. Control patients with aortopathy who did not have surgery were matched for age, sex, body size, and d_MAA (n = 20: 52 ± 14 years; 3 women; d_SOV/d_MAA = 42 ± 4/42 ± 4 mm). Regional aortic 3D systolic peak WSS was calculated. An atlas of WSS normal values was used to quantify the percentage of at-risk tissue area with abnormally high WSS, excluding the area to be resected/graft. ResultsPeak WSS and at-risk area showed low interobserver variability (≤0.09 [−0.3; 0.5] Pa and 1.1% [−7%; 9%], respectively). In control patients, WSS was stable over time (follow-up–baseline differences ≤0.02 Pa and 0.0%, respectively). Proximal aortic WSS decreased after AVR (n = 5; peak WSS difference ≤−0.41 Pa and at-risk area ≤−10%, P < .05 vs controls). WSS was increased after ARR in regions distal to the graft (peak WSS difference ≥0.16 Pa and at-risk area ≥4%, P < .05 vs AVR). Follow-up duration had no significant effects on these WSS changes, except when comparing ascending aortic peak WSS between ARR and AVR (P = .006). ConclusionsSerial perioperative 4D flow MRI investigations showed distinct patterns of postsurgical changes in aortic WSS, which included both reductions and translocations. Larger longitudinal studies are warranted to validate these findings with clinical outcomes and prediction of risk of future aortic events.

Theoretical and computational investigation of optimal wall shear stress in bifurcations: a generalization of Murray’s law

In this study, the optimal distribution of Wall Shear Stress (WSS) in a bifurcation and its effect on the morphology of blood vessels were investigated. The optimal WSS was obtained through minimization of energy loss due to friction and metabolic consumption. It was shown that the optimal WSS is a function of metabolic rate, fluid properties, diameter, and flow regime. For fully developed laminar and turbulent flows different patterns of WSS were observed. For laminar flows WSS is constant but for turbulent flows WSS is a function of diameter such that the exponent of diameter varies by tube relative roughness. Based on the optimal WSS and conservation of mass, the optimal relationship between diameters of mother and daughters’ vessels was obtained for different flow regimes. Also, it was theoretically shown that the optimal distribution of WSS in a bifurcation minimizes flow resistance as well as energy loss. In addition, it was demonstrated that the specific relationship between the length and diameters of a blood vessel and optimal relationship between diameters lead to optimal WSS distribution. Finally, the numerical simulation was used to investigate the effect of Reynolds number on the optimal WSS and flow resistance, and to verify the theoretical formula predictions, obtained in this work.

TCT-454 Impact of Underexpansion on IVUS-Derived Wall Shear Stress Patterns with Bioresorbable Scaffolds and Metallic DES: Insights from the ABSORB III Imaging Substudy

Wall shear stress (WSS) following stent deployment may affect strut healing patterns through established mechanobiologic pathways. Fused angiographic and IVUS-derived WSS were calculated in coronary arteries from patients enrolled in the ABSORB III Imaging study (n=92), randomized 2:1 to Absorb