Computational model for simulation of vascular adaptation following vascular access surgery in haemodialysis patients

An important number of surgical procedures for creation of vascular access (VA) in haemodialysis patients still results in non-adequate increase in blood flow (non-maturation). The rise in blood flow in arteriovenous shunts depends on vascular remodelling. Computational tools to predict the outcome of VA surgery would be important in this clinical context. The aim of our investigation was then to develop a 0D/1D computational model of arm vasculature able to simulate vessel wall remodelling and related changes in blood flow. We assumed that blood vessel remodelling is driven by peak wall shear stress. The model was calibrated with previously reported values of radial artery diameter and blood flow after end-to-end distal fistula creation. Good agreement was obtained between predicted changes in VA flow and in arterial diameter after surgery and corresponding measured values. The use of this computational model may allow accurate vascular surgery planning and ameliorate VA surgery outcomes.     

彩色多普勒超声对尿毒症血液透析患者动静脉内瘘的术前及术后监测效果分析

目的:探讨与分析彩色多普勒超声对尿毒症血液透析患者动静脉内瘘的术前及术后监测效果。方法:选择2017年2月至2019年5月在本院诊治的尿毒症血液透析并行自体动静脉内瘘的患者90例,在术前1-3 d与术后3个月进行超声监测,记录超声特征。记录患者术后内瘘失功、并发症发生情况并进行相关性分析。结果:所有患者都顺利完成自体动静脉内瘘;术后3个月患者自体动静脉内瘘在超声上表现为"u"或"v"形管状结构,表现为高速低阻动静脉瘘血流频谱,瘘口处彩色血流均显示为五彩镶嵌紊乱血流。术后3个月患者的头静脉与桡动脉内径、血流量都高于术前(P0.05)。90例患者术后3个月发生血栓形成2例、狭窄1例和静脉瘤样扩张4例,并发症发生率为7.8%。同时发生8例动静脉内瘘失功,发生率为8.9%;Pearson相关分析法显示术后动静脉内瘘失功、并发症发生情况与头静脉、桡动脉内径与血流量存在显著相关性(P0.05)。结论:彩色多普勒超声应用于尿毒症血液透析患者及动静脉内瘘患者可监测内瘘血流动力学、血管形态学变化,能够客观评价内瘘失功与并发症发生情况。     

Sequential venous anastomosis design to enhance patency of arterio-venous grafts for hemodialysis

Arterio-venous grafts (AVGs), the second best option as long-term vascular access for hemodialysis, face major issues of stenosis mainly due to development of intimal hyperplasia at the venous anastomosis which is linked to unfavorable hemodynamic conditions. We have investigated computationally the utility of a coupled sequential venous anastomotic design to replace conventional end-to-side (ETS) venous anastomosis, in order to improve the hemodynamic environment and consequently enhance the patency of AVGs. Two complete vascular access models with the conventional and the proposed venous anastomosis configurations were constructed. Three-dimensional, pulsatile blood flow through the models was simulated, and wall shear stress (WSS)-based hemodynamic parameters were calculated and compared between the two models. Simulation results demonstrated that the proposed anastomotic design provides: (i) a more uniform and smooth flow at the ETS anastomosis, without flow impingement and stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis; (ii) more uniform distribution of WSS and substantially lower WSS gradients on the venous wall; and (iii) a spare route for the blood flow to the vein, to avoid re-operation in case of stenosis. The distinctive hemodynamic advantages observed in the proposed anastomotic design can enhance the patency of AVGs.     

A Novel Murine Model of Arteriovenous Fistula Failure: The Surgical Procedure in Detail

The arteriovenous fistula (AVF) still suffers from a high number of failures caused by insufficient remodeling and intimal hyperplasia from which the exact pathophysiology remains unknown. In order to unravel the pathophysiology a murine model of AVF-failure was developed in which the configuration of the anastomosis resembles the preferred situation in the clinical setting. A model was described in which an AVF is created by connecting the venous end of the branch of the external jugular vein to the side of the common carotid artery using interrupted sutures. At a histological level, we observed progressive stenotic intimal lesions in the venous outflow tract that is also seen in failed human AVFs. Although this procedure can be technically challenging due to the small dimensions of the animal, we were able to achieve a surgical success rate of 97% after sufficient training. The key advantage of a murine model is the availability of transgenic animals. In view of the different proposed mechanisms that are responsible for AVF failure, disabling genes that might play a role in vascular remodeling can help us to unravel the complex pathophysiology of AVF failure.     

The haemodynamic effect of an adjustable band in an arteriovenous fistula

A number of treatment approaches exist for excessive flowrate arteriovenous fistulae. Banding has a number of advantages, yet there is concern over its use due to reported high post-surgery thrombosis rates. A computational study is conducted of a new technique, to elucidate the hemodynamics present in the process. The key improvement involves the use of an adjustable band which can be used to optimise the flowrate during the surgery. The pressure and flowrate changes are apparent from the computational results and the computational results also demonstrate that further optimization may be possible. We then present a small cohort of five cases where the new banding procedure has been implemented with success. The new technique was combined with intra-operative ultrasound flow monitoring.     

尿毒症血液透析患者血清Lp-PLA2、FGF-23与自体动静脉内瘘成熟不良的关系研究

摘要 目的：探讨尿毒症血液透析患者血清脂蛋白相关磷脂酶A2（Lp-PLA2）、成纤维细胞生长因子-23（FGF-23）与自体动静脉内瘘（AVF）成熟不良的关系。方法：选取2021年2月～2022年12月联勤保障部队第908医院肾内科收治的170例接受血液透析的尿毒症患者,根据AVF成熟情况分为成熟不良组57例和成熟组113例。采用酶联免疫吸附法检测血清Lp-PLA2、FGF-23水平。通过多因素Logistic回归分析尿毒症血液透析患者AVF成熟不良的影响因素,受试者工作特征（ROC）曲线分析血清Lp-PLA2、FGF-23水平对尿毒症血液透析患者AVF成熟不良的预测效能。结果：成熟不良组血清Lp-PLA2、FGF-23水平高于成熟组（P＜0.05）。多因素Logistic回归分析显示,血磷、低密度脂蛋白胆固醇（LDL-C）、Lp-PLA2、FGF-23升高为尿毒症血液透析患者AVF成熟不良的独立危险因素（P＜0.05）。ROC曲线分析显示,血清Lp-PLA2、FGF-23水平单独和联合预测尿毒症血液透析患者AVF成熟不良的曲线下面积（AUC）分别为0.725、0.763、0.822,血清Lp-PLA2、FGF-23水平联合预测的AUC最大。结论：尿毒症血液透析患者血清Lp-PLA2、FGF-23水平升高与AVF成熟不良独立相关,血清Lp-PLA2、FGF-23水平联合对AVF成熟不良的预测效能良好。     

Computational fluid dynamics study of common stent models inside idealised curved coronary arteries

The haemodynamic behaviour of blood inside a coronary artery after stenting is greatly affected by individual stent features as well as complex geometrical properties of the artery including tortuosity and curvature. Regions at higher risk of restenosis, as measured by low wall shear stress (WSS < 0.5 Pa), have not yet been studied in detail in curved stented arteries. In this study, three-dimensional computational modelling and computational fluid dynamics methodologies were used to analyse the haemodynamic characteristics in curved stented arteries using several common stent models. Results in this study showed that stent strut thickness was one major factor influencing the distribution of WSS in curved arteries. Regions of low WSS were found behind struts, particularly those oriented at a large angle relative to the streamwise flow direction. These findings were similar to those obtained in studies of straight arteries. An uneven distribution of WSS at the inner and outer bends of curved arteries was observed where the WSS was lower at the inner bend. In this study, it was also shown that stents with a helical configuration generated an extra swirling component of the flow based on the helical direction; however, this extra swirl in the flow field did not cause significant changes on the distribution of WSS under the current setup.     

Enhanced External Counterpulsation Treatment May Intervene The Advanced Atherosclerotic Plaque Progression by Inducing The Variations of Mechanical Factors: A 3D FSI Study Based on in vivo Animal Experiment

Growing evidences suggest that long-term enhanced external counterpulsation (EECP) treatment can inhibit the initiation of atherosclerotic lesion by improving the hemodynamic environment in aortas. However, whether this kind procedure will intervene the progression of advanced atherosclerotic plaque remains elusive and causes great concern in its clinical application presently. In the current paper, a pilot study combining animal experiment and numerical simulation was conducted to investigate the acute mechanical stress variations during EECP intervention, and then to assess the possible chronic effects. An experimentally induced hypercholesterolemic porcine model was developed and the basic hemodynamic measurement was performed in vivo before and during EECP treatment. Meanwhile, A 3D fluid-structure interaction (FSI) model of blood vessel with symmetric local stenosis was developed for the numerical calculation of some important mechanical factors. The results show that EECP augmented 12.21% of the plaque wall stress (PWS), 57.72% of the time average wall shear stress (AWSS) and 43.67% of the non-dimensional wall shear stress gradient (WSSGnd) at throat site of the stenosis. We suggest that long-term EECP treatment may intervene the advanced plaque progression by inducing the significant variations of some important mechanical factors, but its proper effects will need a further research combined follow-up observation in clinic.     

Design of cellular porous biomaterials for wall shear stress criterion

The microfluidic environment provided by implanted prostheses has a decisive influence on the viability, proliferation and differentiation of cells. In bone tissue engineering, for instance, experiments have confirmed that a certain level of wall shear stress (WSS) is more advantageous to osteoblastic differentiation. This paper proposes a level‐set‐based topology optimization method to regulate fluidic WSS distribution for design of cellular biomaterials. The topological boundary of fluid phase is represented by a level‐set model embedded in a higher‐dimensional scalar function. WSS is determined by the computational fluid dynamics analysis in the scale of cellular base cells. To achieve a uniform WSS distribution at the solid–fluid interface, the difference between local and target WSS is taken as the design criterion, which determines the speed of the boundary evolution in the level‐set model. The examples demonstrate the effectiveness of the presented method and exhibit a considerable potential in the design optimization and fabrication of new prosthetic cellular materials for bioengineering applications. Biotechnol. Bioeng. 2010;107:737–746. © 2010 Wiley Periodicals, Inc.     

Modeling and design of optimal flow perfusion bioreactors for tissue engineering applications

Perfusion bioreactors have been used in different tissue engineering applications because of their consistent distribution of nutrients and flow-induced shear stress within the tissue-engineering scaffold. A widely used configuration uses a scaffold with a circular cross-section enclosed within a cylindrical chamber and inlet and outlet pipes which are connected to the chamber on either side through which media is continuously circulated. However, fluid-flow experiments and simulations have shown that the majority of the flow perfuses through the center. This pattern creates stagnant zones in the peripheral regions as well as in those of high flow rate near the inlet and outlet. This non-uniformity of flow and shear stress, owing to a circular design, results in limited cell proliferation and differentiation in these areas. The focus of this communication is to design an optimized perfusion system using computational fluid dynamics as a mathematical tool to overcome the time-consuming trial and error experimental method. We compared the flow within a circular and a rectangular bioreactor system. Flow simulations within the rectangular bioreactor are shown to overcome the limitations in the circular design. This communication challenges the circular cross-section bioreactor configuration paradigm and provides proof of the advantages of the new design over the existing one.     

潮间带盐沼植物种子及实生苗漂浮起动临界剪切应力研究

盐沼是分布在海陆过渡区域,以大型草本植物为优势种的潮间带生态系统。在潮间带生态系统中,盐沼植物的种子和实生苗在潮流作用下的漂浮起动是盐沼植物自然扩散的重要前提,决定了盐沼植物能否实现有效扩散和长距离传播。然而,目前缺乏有关盐沼植物繁殖体在复杂潮滩环境下漂浮起动扩散过程的定量研究。以长江口典型盐沼先锋物种海三棱藨草(Scirpus mariqueter)为研究对象,应用U-GEMS微观侵蚀系统,测定了在不同沉积物底质条件下,海三棱藨草种子及不同萌发阶段实生苗漂浮起动时的临界剪切应力,定量分析不同萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的影响。研究结果表明：(1)不同种子萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的临界剪切应力均有极显著影响(P<0.01);(2)随着萌发阶段的进展,海三棱藨草实生苗漂浮起动所需的临界剪切应力逐渐减小,因而随潮流漂浮起动进而扩散的机会也相应增大;(3)相比于淤泥质潮滩底质,海三棱藨草种子和实生苗在粉砂质潮滩更易于漂浮起动。研究结果丰富了盐沼植物在潮间带自然扩散过程和机理的研究,也为今后长江口及其他区域开展高效、低成本、以种子为修复...