Blood Flow In Large Arteries Research Articles

Abstract TMP55: Arterial Spin Labeling Study Immediately After Thrombectomy: A Mechanism of Poor Prognosis Despite Recanalization

Introduction: In thrombectomy, the mechanism of poor prognosis despite complete recanalization is still unclear. Hyperperfusion may be a such poor prognostic mechanism. Residual microcirculatory dysfunction after restored large artery blood flow (no-reflow phenomenon) may also be a potential mechanism. MRI with arterial spin labeling (ASL) can easily assess cerebral perfusion. We here investigated the mechanism of poor prognosis despite recanalization by analyzing ASL images immediately after thrombus retrieval. Methods: This study included 41 consecutive cases (July 2019 to July 2023) with ICA or M1 embolic occlusions who underwent successful thrombectomy (mTICI3) and immediate post-operative ASL-MRI. Regional cerebral blood flow (CBF) on the ASL images were automatically quantified by means of 3DSRT software using 318 constant ROIs classified into 12 segments in each hemisphere. We evaluated the contralesional CBF ratio not only for the entire middle cerebral artery area and each of its segments, but also for each 3DSRT ROIs around the central sulcus (central arterial segment including 28 ROIs). These results of the post-operative ASL evaluation were compared between the favorable prognosis group (mRS 0-2 at 3 months) and the poor prognosis group (mRS 3-6). Results: There was no difference between the poor prognosis group (n=14) and the favorable prognosis group (n=27) in the comparison of the contralesional CBF ratio for the entire middle cerebral artery area or for each segment. However, the number of ROIs in the central segment decreased by 10% CBF or more and by 20% CBF or more compared to the contralesional side were significantly higher (both p<0.01) in the poor prognosis group (19.1% against 11.8%, 3.1% against 0%, respectively). There was no difference in comparing the number of ROIs with increased CBF. Conclusions: This study showed that a high number of small-area (ROI) circulatory dysfunction (suggesting no-reflow phenomenon) was associated with a poor prognosis despite complete recanalization.

Direct numerical simulation of a pulsatile flow in a stenotic channel using immersed boundary method

AbstractA three‐dimensional direct numerical simulation model coupled with the immersed boundary method has been developed to simulate a pulsatile flow in a planar channel with single and double one‐sided semicircular constrictions. For relevance to blood flow in large arteries, simulations have been performed at Reynolds numbers of 750 and 1000. Flow physics and resultant wall shear stress (WSS)‐based hemodynamic parameters are presented. The instantaneous vortex dynamics, mean flow characteristics, and turbulent energy spectra are evaluated for flow physics. Subsequently, three WSS‐based parameters, namely the time‐averaged WSS, oscillatory shear index, and relative residence time, are calculated over the stenotic wall and correlated with flow physics to identify the regions prone to atherosclerotic plaque progression. Results show that the double stenotic channel leads to high‐intensity and broadband turbulent characteristics downstream, promoting critical values of the WSS‐based parameters in the post‐stenotic areas. In addition, the inter‐space area between two stenoses displays multiple strong recirculations, making this area highly prone to atherosclerosis progression. The effect of stenosis degree on the WSS‐based parameters is studied up to 60% degree. As the degree of occlusion is increased, larger regions are involved with the nonphysiological ranges of the WSS‐based parameters.

INVESTIGATION OF THE BLOOD FLOW IN DEFORMABLE VESSELS USING STABILIZED FINITE ELEMENT METHOD

The study and simulation of blood flow in the cardiovascular system have many applications such as pathologies studies, surgical planning, and design of medical devices. Several works within this area consider the problem using a rigid wall assumption, while blood velocity and pressure in large arteries are greatly influenced by vessel wall dynamics. The Coupled Momentum Method (CMM) is based on a strong coupling of degrees-of-freedom of the fluid and the solid domains. This coupling is made by considering that the deformation of the wall, in a variational level, become a boundary condition for the fluid domain. As an advantage, description of motion (Eulerian) may be kept the same and a fixed mesh. In this study, blood is considered a Newtonian fluid and the wall a thin-walled linear elastic. This work is focused on using fluid-structure interaction in 3D geometries to evaluate the blood and vessel dynamics in contrast to the rigid wall formulation what is considered only a fluid dynamic problem. For realistic and physiological parameters, CMM has demonstrated to be a good alternative for the simulation of blood flow in large arteries by virtue of representing more realistic phenomena than a rigid wall model. The results were obtained using FEniCS and Python, and are in agreement with the theoretical and numerical solutions from the literature.

Wall shear stress fixed points in cardiovascular fluid mechanics

Complex blood flow in large arteries creates rich wall shear stress (WSS) vectorial features. WSS acts as a link between blood flow dynamics and the biology of various cardiovascular diseases. WSS has been of great interest in a wide range of studies and has been the most popular measure to correlate blood flow to cardiovascular disease. Recent studies have emphasized different vectorial features of WSS. However, fixed points in the WSS vector field have not received much attention. A WSS fixed point is a point on the vessel wall where the WSS vector vanishes. In this article, WSS fixed points are classified and the aspects by which they could influence cardiovascular disease are reviewed. First, the connection between WSS fixed points and the flow topology away from the vessel wall is discussed. Second, the potential role of time-averaged WSS fixed points in biochemical mass transport is demonstrated using the recent concept of Lagrangian WSS structures. Finally, simple measures are proposed to quantify the exposure of the endothelial cells to WSS fixed points. Examples from various arterial flow applications are demonstrated.

A Systematic Review and Meta-Analysis of the In Vivo Haemodynamic Effects of Δ⁸-Tetrahydrocannabinol.

∆9-Tetrahydrocannabinol (THC) has complex effects on the cardiovascular system. We aimed to systematically review studies of THC and haemodynamic alterations. PubMed, Medline, and EMBASE were searched for relevant studies. Changes in blood pressure (BP), heart rate (HR), and blood flow (BF) were analysed using the Cochrane Review Manager Software. Thirty-one studies met the eligibility criteria. Fourteen publications assessed BP (number, n = 541), 22 HR (n = 567), and 3 BF (n = 45). Acute THC dosing reduced BP and HR in anaesthetised animals (BP, mean difference (MD) −19.7 mmHg, p < 0.00001; HR, MD −53.49 bpm, p < 0.00001), conscious animals (BP, MD −12.3 mmHg, p = 0.0007; HR, MD −30.05 bpm, p < 0.00001), and animal models of stress or hypertension (BP, MD −61.37 mmHg, p = 0.03) and increased cerebral BF in murine stroke models (MD 32.35%, p < 0.00001). Chronic dosing increased BF in large arteries in anaesthetised animals (MD 21.95 mL/min, p = 0.05) and reduced BP in models of stress or hypertension (MD −22.09 mmHg, p < 0.00001). In humans, acute administration increased HR (MD 8.16 bpm, p < 0.00001). THC acts differently according to species and experimental conditions, causing bradycardia, hypotension and increased BF in animals; and causing increased HR in humans. Data is limited, and further studies assessing THC-induced haemodynamic changes in humans should be considered.

On the choice of outlet boundary conditions for patient-specific analysis of aortic flow using computational fluid dynamics

Boundary conditions (BCs) are an essential part in computational fluid dynamics (CFD) simulations of blood flow in large arteries. Although several studies have investigated the influence of BCs on predicted flow patterns and hemodynamic wall parameters in various arterial models, there is a lack of comprehensive assessment of outlet BCs for patient-specific analysis of aortic flow. In this study, five different sets of outlet BCs were tested and compared using a subject-specific model of a normal aorta. Phase-contrast magnetic resonance imaging (PC-MRI) was performed on the same subject and velocity profiles extracted from the in vivo measurements were used as the inlet boundary condition. Computational results obtained with different outlet BCs were assessed in terms of their agreement with the PC-MRI velocity data and key hemodynamic parameters, such as pressure and flow waveforms and wall shear stress related indices. Our results showed that the best overall performance was achieved by using a well-tuned three-element Windkessel model at all model outlets, which not only gave a good agreement with in vivo flow data, but also produced physiological pressure waveforms and values. On the other hand, opening outlet BCs with zero pressure at multiple outlets failed to reproduce any physiologically relevant flow and pressure features.

Low-Shapiro hydrostatic reconstruction technique for blood flow simulation in large arteries with varying geometrical and mechanical properties

The purpose of this work is to construct a simple, efficient and accurate well-balanced numerical scheme for one-dimensional (1D) blood flow in large arteries with varying geometrical and mechanical properties. As the steady states at rest are not relevant for blood flow, we construct two well-balanced hydrostatic reconstruction techniques designed to preserve low-Shapiro number steady states that may occur in large network simulations. The Shapiro number Sh=u/c is the equivalent of the Froude number for shallow water equations and the Mach number for compressible Euler equations. The first is the low-Shapiro hydrostatic reconstruction (HR-LS), which is a simple and efficient method, inspired from the hydrostatic reconstruction technique (HR). The second is the subsonic hydrostatic reconstruction (HR-S), adapted here to blood flow and designed to exactly preserve all subcritical steady states. We systematically compare HR, HR-LS and HR-S in a series of single artery and arterial network numerical tests designed to evaluate their well-balanced and wave-capturing properties. The results indicate that HR is not adapted to compute blood flow in large arteries as it is unable to capture wave reflections and transmissions when large variations of the arteries' geometrical and mechanical properties are considered. On the contrary, HR-S is exactly well-balanced and is the most accurate hydrostatic reconstruction technique. However, HR-LS is able to compute low-Shapiro number steady states as well as wave reflections and transmissions with satisfying accuracy and is simpler and computationally less expensive than HR-S. We therefore recommend using HR-LS for 1D blood flow simulations in large arterial network simulations.

Fluid responsiveness in acute circulatory failure.

Although fluid resuscitation of patients having acute circulatory failure is essential, avoiding unnecessary administration of fluids in these patients is also important. Fluid responsiveness (FR) is defined as the ability of the left ventricle to increase its stroke volume (SV) in response to fluid administration. The objective of this review is to provide the recent advances in the detection of FR and simplify the physiological basis, advantages, disadvantages, and cut-off values for each method. This review also highlights the present gaps in literature and provides future thoughts in the field of FR.Static methods are generally not recommended for the assessment of FR. Dynamic methods for the assessment of FR depend on heart-lung interactions. Pulse pressure variation (PPV) and stroke volume variation (SVV) are the most famous dynamic measures. Less-invasive dynamic parameters include plethysmographic-derived parameters, variation in blood flow in large arteries, and variation in the diameters of central veins. Dynamic methods for the assessment of FR have many limitations; the most important limitation is spontaneous breathing activity.Fluid challenge techniques were able to overcome most of the limitations of the dynamic methods. Passive leg raising is the most popular fluid challenge method. More simple techniques have been recently introduced such as the mini-fluid challenge and 10-s fluid challenge. The main limitation of fluid challenge techniques is the need to trace the effect of the fluid challenges on SV (or any of its derivatives) using a real-time monitor. More research is needed in the field of FR taking into consideration not only the accuracy of the method but also the ease of implementation, the applicability on a wider range of patients, the time needed to apply each method, and the feasibility of its application by acute care physicians with moderate and low experience.

Stochastic dynamics in a fluid--plate interaction model with the only longitudinal deformations of the plate

We consider a stochastically perturbed coupled system consisting of linearized 3D Navier--Stokes equations in a bounded domain and the classical (nonlinear) elastic plate equation for in-plane motions on a flexible flat part of the boundary. This kind of models arises in the study of blood flows in large arteries. Our main result states the existence of a random pullback attractor of finite fractal dimension. Our argument is based on some modification of the method of quasi-stability estimates recently developed for deterministic systems.

A Brief History of USNCB: Motivation and Formation

A Brief History of USNCB: Motivation and Formation

Pulsatile blood flow in large arteries: comparative study of Burton’s and McDonald’s models

To get a clear picture of the pulsatile nature of blood flow and its role in the pathogenesis of atherosclerosis, a comparative study of blood flow in large arteries is carried out using the two widely used models, McDonald’s and Burton’s models, for the pressure gradient. For both models, the blood velocity in the lumen is obtained analytically. Elaborate investigations on the wall shear stress (WSS) and oscillatory shear index (OSI) are carried out. The results are in good agreement with the available data in the literature. The superiority of McDonald’s model in capturing the pulsatile nature of blood flow, especially the OSI, is highlighted. The present investigation supports the hypothesis that not only WSS but also OSI are the essential features determining the pathogenesis of atherosclerosis. Finally, by reviewing the limitations of the present investigation, the possibility of improvement is explored.

Prospects for Multimodality Imaging in Peripheral Artery Disease

Asymptomatic peripheral artery disease (PAD) is an important marker for elevated risk of coronary and cerebrovascular disease. Symptomatic PAD adds to this burden by affecting quality of life and limiting function. This runs the spectrum of claudication impeding walking and mobility to critical limb ischemia with rest pain, gangrene, and risk of major amputation.1 Article see p 92 Symptomatic PAD is a product of several abnormal factors. These include impaired blood flow to muscle and limb tissue because of stenosis or occlusion of the large conduit arteries, endothelial dysfunction affecting blood flow in all arteries, and abnormal muscle bioenergetics.2 Therapies for symptomatic PAD target these defects.2–7 For example, revascularization improves blood flow in large arteries, and risk factor modification, such as smoking cessation, walking programs, and hydroxy-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, aims to improve endothelial function and muscle bioenergetics during exercise. Arteriogenesis and angiogenesis of the small arteries and capillaries may be mechanisms for some of the benefits from risk factor modification and are the foundation for cell-based therapies that offer the potential for improved perfusion in critical limb ischemia. Currently, the clinical diagnosis of PAD relies on clinical symptoms, clinical signs, and physiological tests of blood flow at rest and exercise. These include …

Numerical study of pulsatile channel flows undergoing transition triggered by a modelled stenosis

In this research, we numerically investigate the physics of pulsatile flows confined within a 3-dimensional channel with a modelled stenosis formed eccentrically on the upper wall using the method of large-eddy simulation (LES). An advanced dynamic nonlinear subgrid-scale stress model was utilized to conduct numerical simulations and its predictive performance was examined in comparison with that of the conventional dynamic model. The Womersley number tested in the simulation was fixed at 10.5 and the Reynolds numbers tested were set to 750 and 2000, which are characteristics of human blood flows in large arteries. An in-house LES code, based on curvilinear Cartesian coordinates, has been developed to conduct the unsteady numerical simulations using three different grid systems. The physical characteristics of the flow field have been studied in terms of the resolved mean velocity, turbulence kinetic energy, viscous wall shear stress, resolved and subgrid-scale turbulent shear stresses, local kinetic energy fluxes between the filtered and subgrid scales, and turbulence energy spectra along the central streamline of the domain. Triggered by the stenosis, the flow field driven by the pulsatile inlet condition undergoes laminar-turbulent-laminar patterns in the streamwise direction. Correspondingly, the slope of the energy spectra deviates significantly from the well-known −5/3 law for the inertial subrange to reflect the transition in the flow patterns.

Acute treatment and prevention of stroke

Nitric oxide (NO) donors are a candidate target for lowering BP in patients with acute stroke. Nitric oxide is a key mediator as a neurotransmitter, in the regulation of cerebral blood flow (CBF) and systemic haemodynamics, and in terms of platelet and leucocyte function. It is potentially neuroprotective 3 and has peripheral vasoactive and cardioprotective properties. A series of three small, phase 2, randomised controlled trials (RCTs) assessed the safety and effects of transdermal glyceryl trinitrate (GTN), an NO donor, in acute or recent stroke. 4,5 Transdermal administration of GTN was chosen as it has the advantages that administration is easy and visible, treatment can be stopped by removal of the patch if necessary and the presence of dysphagia, a common complication of stroke, will not interfere with drug delivery. In the first trial (37 patients randomised in a ratio of 1:1 to active treatment or placebo), GTN reduced 24-hour BP, measured using ambulatory blood pressure monitoring, over the first day, although tachyphylaxis was apparent by day 7. In addition, GTN had no antiplatelet effects, assessed through aggregation and expression of surface adhesion molecules, which means that it can be given to patients with PICH. (The finding on platelet function contrasts with the results of an earlier uncontrolled study of intravenous sodium nitroprusside (SNP), in which platelet function was attenuated.) 6 In the second trial (90 patients randomised in a ratio of 2:1 to active treatment or control), GTN increased vascular compliance but had no effect on large artery blood flow determined using transcranial doppler (TCD) assessment of cerebral blood flow velocity and pulsatility index. 4

Coupling schemes for incompressible fluid-structure interaction: implicit, semi-implicit and explicit

Over the last decade, the numerical simulation of incompressible fluid-structure interaction has been a very active research field and the subject of numerous works. This is due, in particular, to the increasing interest of the research community in the simulation of blood flows in large arteries. In this context, the fluid equations have to be solved in a moving domain and the incompressibility constraint makes the coupling sensitive to the added-mass effect. As a result, the solution procedure has to be designed carefully in order to guarantee efficiency without compromising numerical stability. In this paper, we review some of the coupling schemes recently proposed in the literature. Some numerical results that show the effectiveness of the novel approaches are also presented.

A global attractor for a fluid-plate interaction model accounting only for longitudinal deformations of the plate

We study asymptotic dynamics of a coupled system consisting of linearized 3D Navier--Stokes equations in a bounded domain and the classical (nonlinear) elastic plate equation for in-plane motions on a flexible flat part of the boundary. The main peculiarity of the model is the assumption that the transversal displacements of the plate are negligible relative to in-plane displacements. This kind of models arises in the study of blood flows in large arteries. Our main result states the existence of a compact global attractor of finite dimension. We also show that the corresponding linearized system generates exponentially stable $C_0$-semigroup. We do not assume any kind of mechanical damping in the plate component. Thus our results means that dissipation of the energy in the fluid due to viscosity is sufficient to stabilize the system.

Hemorheology and Microvascular Disorders

The present review presents basic concepts of blood rheology related to vascular diseases. Blood flow in large arteries is dominated by inertial forces exhibited at high flow velocities, while viscous forces (i.e., blood rheology) play an almost negligible role. When high flow velocity is compromised by sudden deceleration as at a bifurcation, endothelial cell dysfunction can occur along the outer wall of the bifurcation, initiating inflammatory gene expression and, through mechanotransduction, the cascade of events associated with atherosclerosis. In sharp contrast, the flow of blood in microvessels is dominated by viscous shear forces since the inertial forces are negligible due to low flow velocities. Shear stress is a critical parameter in microvascular flow, and a force-balance approach is proposed for determining microvascular shear stress, accounting for the low Reynolds numbers and the dominance of viscous forces over inertial forces. Accordingly, when the attractive forces between erythrocytes (represented by the yield stress of blood) are greater than the shear force produced by microvascular flow, tissue perfusion itself cannot be sustained, leading to capillary loss. The yield stress parameter is presented as a diagnostic candidate for future clinical research, specifically, as a fluid dynamic biomarker for microvascular disorders. The relation between the yield stress and diastolic blood viscosity (DBV) is described using the Casson model for viscosity, from which one may be able determine thresholds of DBV where the risk of microvascular disorders is high.

Murine Cerebral Malaria Is Associated with a Vasospasm-Like Microcirculatory Dysfunction, and Survival upon Rescue Treatment Is Markedly Increased by Nimodipine

Brain hemodynamics in cerebral malaria (CM) is poorly understood, with apparently conflicting data showing microcirculatory hypoperfusion and normal or even increased blood flow in large arteries. Using intravital microscopy to assess the pial microvasculature through a closed cranial window in the murine model of CM by Plasmodium berghei ANKA, we show that murine CM is associated with marked decreases (mean: 60%) of pial arteriolar blood flow attributable to vasoconstriction and decreased blood velocity. Leukocyte sequestration further decreased perfusion by narrowing luminal diameters in the affected vessels and blocking capillaries. Remarkably, vascular collapse at various degrees was observed in 44% of mice with CM, which also presented more severe vasoconstriction. Coadministration of artemether and nimodipine, a calcium channel blocker used to treat postsubarachnoid hemorrhage vasospasm, to mice presenting CM markedly increased survival compared with artemether plus vehicle only. Administration of nimodipine induced vasodilation and increased pial blood flow. We conclude that vasoconstriction and vascular collapse play a role in murine CM pathogenesis and nimodipine holds potential as adjunctive therapy for CM.

Cerebral Malaria: A Vasculopathy

Cerebral Malaria: A Vasculopathy

Modeling and interpretation of the bioelectrical impedance signal for the determination of the local arterial stiffness

Stiffness of the large arteries (e.g., aorta) plays an important role in the pathogenesis of cardiovascular diseases. To date, the reference method for the determination of regional arterial stiffness is the measurement of the carotid-femoral pulse wave velocity (PWV) by tonometric techniques. However, this method suffers from several drawbacks and it remains limited in clinical routine. In the present study, the authors propose a new method based on the analysis of bioelectrical impedance (BI) signals for the determination of the local arterial stiffness. They show, from a theoretical model, a novel interpretation of the BI signals and they establish the relationship between the variations in the BI signal and the kinetic energy of the blood flow in large arteries. From this model, BI signals are simulated in the thigh and compared to experimental BI data. Finally, from the model, they propose a new index (Ira) related to the properties of the large artery for the determination of the local arterial stiffness. The results show a good correlation between the simulated and the experimental BI signals. The same variations for both of them with different characteristics for rigid and elastic arteries can be observed. The measurement of the Ira index on 20 subjects at rest (mean age of 44 +/- 16 yr) for the determination of the local aortic stiffness presents a significant correlation with the PWV reference method (R2=0.77; P<0.0001 with the Spearman correlation coefficient and Ira= 4.25*PWV+23.54). All the results suggest that the theoretical model and the new index could give a reliable estimate of local arterial stiffness.