瓣后血流湍流剪应力的在体无创测量的计算机软件技术

湍流剪应力（TS）被认为是导致心血管内皮层损伤和生物瓣钙化的重要原因,其研究已由离体的模拟实验逐步发展为在体的无损测量。本文提出了基于彩色超声多普斯败血流速度频谱分析图象的计算机图象处理的TSSbiPF无创测量方法及软件。首先将超声多普勒仪记录的待测位点的至少5个心动周期的速度频谱图象经图象捕获卡数字化后采集至计算机,通过专门的图象分析算法,得到各个心动周期内速度的拟合曲线。在每个速度曲线上的E（或动点前后以sins为间隔各取2个时点,连同E（或周点共5个时刻的瞬时速度值Uij（i＝l,2,3,4,5…n;j＝1,2,3,…     

与多普勒超声相结合的人体二尖瓣狭窄下游湍流剪应力二维有限元分析

目的 探讨一种与多普勒超声相结合的人体二尖瓣狭窄下游湍流剪应力地维有限元分析方法。方法 采用多普勒超声无创检测技术,将体内实时采集到的左心腔二维超声图像和左房、左室壁平均运动速度作为边界条件,对一组二尖瓣狭窄病人随访期间二尖瓣下游湍流剪应力（turbulent shear stress,TSS)进行计算机数值模拟、二维有限元分析。结果 有限元分析显示：TSS在两次随访前后均存在显著性差异（P＜0．05）,与瓣膜病变Wilkins评分呈明显正相关（r:0.80-0.82);无论病变和狭窄程度怎样,跨瓣血流核心区位点TSS始终低于边界各位点,其最大值＜80N／m^2,结果同以往研究结论一致。结论 二尖瓣狭窄下游所产生的TSS与瓣膜病变进展密切相关。有限元法对局部瓣区和整个流场中TSS和速度大小与分布的描述较为完整而详细,因此它与多普勒超声技术相结合,使心瓣流场中TSS的体内定量研究既全面而又准确。     

二尖瓣狭窄下游湍流剪应力体内多普勒超声定量检测的方法学研究

为建立与计算机图像分析技术相结合的人体二尖瓣狭窄下游湍流剪应力 (Turbulent shear stree,TSS)多普勒超声定量检测方法。本研究采用多普勒超声技术对正常人和不同程度二尖瓣狭窄病人组的二尖瓣下游血流速度频谱等指标进行多位点记录 ,通过计算机图像分析技术 ,测算出相关位点 TSS大小。结果表明不同程度二尖瓣狭窄组的二尖瓣下游核心位点 TSS与相对扰动强度 (Relative turbulent intensity,Irel)始终低于边界各位点 ;边界位点 TSS、Irel和流场均匀性等指标在正常对照和不同程度狭窄组之间均存在显著性差异 (P<0 .0 5 ) ,并均与有效瓣口面积 (Effective orifice area,EOA)明显相关。结论为二尖瓣有效开口面积越小 ,狭窄越重 ,射流边界 TSS和 Irel越大 ,射流核心区 TSS明显低于边界。研究结果显示 :应用与计算机图像分析相结合的多普勒超声技术所测人体二尖瓣狭窄下游 TSS与流场均匀性等常规多普勒超声指标具有良好的相关性 ,能共同反映不同狭窄程度病人瓣区血流动力学变化 ,因此表明本方法能比较准确地刻画人体二尖瓣狭窄下游 TSS的大小 ,并且 ,还具有安全无创、抗干扰能力强的特点 ,可用于瓣膜病病人瓣区流场中 TSS的定量分析。     

二尖瓣狭窄下游湍流强度体内多普勒超声定量研究

目的以无创的多普勒超声检测方法了解二尖瓣狭窄下游血流不同部位湍流强度特点,探讨湍流剪应力(turbulent shear stress, TSS)、相对扰动强度(relative turbulent intensity, Irel) 与狭窄病变间的相互关系,为深入研究瓣膜疾病发生发展机制与人工心瓣血流动力学提供前期基础和科学依据. 方法应用与计算机图像分析技术相结合的多普勒超声,对一组不同程度二尖瓣狭窄病人二尖瓣下游跨瓣血流不同部位湍流强度进行定量描述. 结果二尖瓣狭窄下游射流区TSS与Irel均明显低于射流周围湍流区.射流区TSS与Irel在不同狭窄程度组间差异均无显著性(p>0.05),而湍流区TSS与 Irel在不同狭窄程度组间差异均存在显著性(p<0.05),并且,T SS和Irel均与有效瓣口面积(effective orifice area, EOA)成明显负相关(r各为-0.84和-0.82).超声显示,绝大部分患者瓣尖部位病变的严重程度远高于瓣膜的其它部分. 结论二尖瓣狭窄下游射流周围湍流区湍流强度远高于射流区,狭窄病变越重,湍流强度越大,而射流区湍流强度与狭窄程度无关.TSS集中分布于湍流区与瓣膜病变的空间对应关系提示,TSS是导致瓣膜病变进行性加重不容忽视的重要因素,其具体作用机制有待进一步研究加以阐明.此外,生物心瓣(bioprosthetic heart valve, BHV)的衰败很可能还与其下游长期存在的TSS有关,值得深入研究.     

二尖瓣狭窄下游湍流强度体内多普勒超声定量研究

目的以无创的多普勒超声检测方法了解二尖瓣狭窄下游血流不同部位湍流强度特点,探讨湍流剪应力(turbulent shear stress,TSS)、相对扰动强度(relative turbulent intensity,Irel)与狭窄病变间的相互关系,为深入研究瓣膜疾病发生发展机制与人工心瓣血流动力学提供前期基础和科学依据.方法应用与计算机图像分析技术相结合的多普勒超声,对一组不同程度二尖瓣狭窄病人二尖瓣下游跨瓣血流不同部位湍流强度进行定量描述.结果二尖瓣狭窄下游射流区TSS与Irel均明显低于射流周围湍流区.射流区TSS与Irel在不同狭窄程度组间差异均无显著性(p>0.05),而湍流区TSS与Irel在不同狭窄程度组间差异均存在显著性(p<0.05),并且,TSS和Irel均与有效瓣口面积(effective orifice area,EOA)成明显负相关(r各为-0.84和-0.82).超声显示,绝大部分患者瓣尖部位病变的严重程度远高于瓣膜的其它部分.结论二尖瓣狭窄下游射流周围湍流区湍流强度远高于射流区,狭窄病变越重,湍流强度越大,而射流区湍流强度与狭窄程度无关.TSS集中分布于湍流区与瓣膜病变的空间对应关系提示,TSS是导致瓣膜病变进行性加重不容忽视的重要因素,其具体作用机制有待进一步研究加以阐明.此外,生物心瓣(bioprosthetic heart     

光导纤维型激光多普勒血流测定仪及其应用

光导纤维型激光多普勒血流测定仪是一种测量血流点速度的极好工具。采用这种仪器,可以从血管横断面上的每一点速度构成血流速度、血管直径和心动周期的三维图像。在本文中简要地介绍光导纤维型激光多普勒血流测定仪的构成原理及其应用。     

保留相同瓣下结构比较不同人工瓣膜下游湍流剪应力的差异

背景：保留瓣下结构可引起瓣膜下游血流受阻,目前有关保留瓣下结构不同人工瓣膜下游血流受阻情况的定量研究尚不深入。 目的：比较保留相同瓣下结构、不同类型人工瓣膜下游血流动力学性能的优劣。 方法：按常规二尖瓣置换方法,在全麻气管插管体外循环下建立标准的猪二尖瓣置换模型。按未保留瓣下结构、保留后瓣瓣下结构以及保留全瓣瓣下结构3种术式处理猪的二尖瓣及其瓣下结构,置换的瓣膜类型为单叶机械瓣膜、双叶机械瓣膜和生物瓣膜。采用多普勒超声结合计算机图像分析技术,对猪保留相同瓣下结构的不同类型的人工瓣膜下游湍流剪应力进行体内定量实验。 结果与结论：未保留瓣下结构的单叶双叶机械人工瓣膜下游血流动力学性能相当,均较生物瓣膜差。保留相同瓣下结构的不同类型人工瓣膜置换后其下游的血流动力学性能以生物瓣膜最佳,双叶机械瓣膜次之,单叶瓣膜最差。     

心瓣流场中湍流剪应力的方法学研究

本文从方法学的角度对目前心瓣流场中湍流剪应力体内外研究方法与检测技术及其优缺点进行了综合评估。鉴于诸多方法各自具有的不足，有关湍流剪应力的研究迄今尚缺乏一种较为理想的方法。指出体内无创研究是今后湍流剪应力的方法学研究的一个主要发展方向，不断普及的RMI与逐步完善的多维彩色多普勒超声技术将成为准确更高、较有前途的湍流剪应力检测方法。     

颅内动脉瘤夹闭手术的血流动力学数值分析

本文利用计算流体力学(CFD)方法对颅内动脉瘤夹闭手术前后血液流场进行三维数值模拟,根据血流动力学对手术方案的可行性进行预估。采用逆向工程软件Mimics对临床CT图像进行三维数字化重构,结合相关脉动血流量,模拟心动周期不同时刻的血流动力学细节。通过计算得到了模型手术前后在心动周期不同时刻的速度场、壁面剪切应力场、压力场的分布特征,对比分析手术前后分叉处的血流速度、壁面剪切应力、壁面压力变化,结果显示术后的血流速度与壁面剪切力显著提高,而壁面压强则明显降低。     

保留瓣下结构的几种机械瓣下游血流动力学多普勒超声研究

了解二尖瓣置换术mitralvalvereplacement,MVR保留瓣下结构对不同类型机械瓣下游血流动力学的影响,为合理选择术式以最大限度减少手术并发症提供科学依据。方法采用彩色多普勒超声结合计算机图像分析技术,对保留瓣下结构的不同类型机械瓣置换术后患者机械瓣下游湍流剪应力turbulentshearstress,TSS等指标进行体内定量研究。结果无论保留全瓣或后瓣,跨瓣血流边界位点TSS在两种不同构型机械瓣组间均存在显著性差异(P<0.05),单叶机械瓣(单叶瓣)TSS较双叶机械瓣(双叶瓣)高。对于单叶瓣,TSS在保留全瓣瓣下结构组(保留全瓣组)、保留后瓣瓣下结构组(保留后瓣组)与未保留瓣下结构组(未保留组)间均存在显著差异(P<0.05)。而对于双叶瓣,保留全瓣组TSS均高于其它2组(P<0.05)。结论保留瓣下结构可改善术后患者心功能,但却在一定程度上增加跨瓣血流扰动性,使下游TSS增大。这种影响以全瓣保留者为著,单叶瓣甚于双叶瓣。对于心功能较差,有必要保留全瓣瓣下结构者,可尽量使用双叶瓣,以减轻对人工心瓣下游血流动力学可能产生的不良影响。     

Models of Flow-Induced Loading on Blood Cells in Laminar and Turbulent Flow,with Application to Cardiovascular Device Flow

Viscous shear stress and Reynolds stress are often used to predict hemolysis and thrombosis due to flow-induced stress on blood elements in cardiovascular devices. These macroscopic stresses are distinct from the true stress on an individual cell, which is determined by the local microscale flow field. In this paper the flow-induced stress on blood cells is calculated for laminar and turbulent flow, using simplified models for cells and for turbulent eddies. The model is applied to estimate shear stress on red blood cells in flow through a prosthetic heart valve, using the energy spectral density measured by Liu et al. [J. Biomech. Eng. 122:118–124, 2000]. Results show that in laminar flow, the maximum stress on a cell is approximately equal to the macroscopic viscous shear stress. In turbulent flow through a prosthetic heart valve, the estimated root mean square of flow-induced stress on a cell is at least an order of magnitude less than the Reynolds stress. The results support the hypothesis that smaller turbulent eddies cause higher stress on cells. However, the stress due to an eddy depends on the velocity scale of the eddy as well as its length scale. For the heart valve flow investigated, turbulence contributes to flow-induced stress on cells almost equally across a broad range of the frequency spectrum. The model suggests that Reynolds stress alone is not an adequate predictor of cell damage in turbulent flow, and highlights the importance of the energy spectral density.     

Experimental Investigation of the Steady Flow Downstream of the St. Jude Bileaflet Heart Valve: A Comparison Between Laser Doppler Velocimetry and Particle Image Velocimetry Techniques

This study investigates turbulent flow, based on high Reynolds number, downstream of a prosthetic heart valve using both laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Until now, LDV has been the more commonly used tool in investigating the flow characteristics associated with mechanical heart valves. The LDV technique allows point by point velocity measurements and provides enough statistical information to quantify turbulent structure. The main drawback of this technique is the time consuming nature of the data acquisition process in order to assess an entire flow field area. Another technique now used in fluid dynamics studies is the PIV measurement technique. This technique allows spatial and temporal measurement of the entire flow field. Using this technique, the instantaneous and average velocity flow fields can be investigated for different positions. This paper presents a comparison of PIV two-dimensional measurements to LDV measurements, performed under steady flow conditions, for a measurement plane parallel to the leaflets of a St. Jude Medical (SJM) bileaflet valve. Comparisons of mean velocity obtained by the two techniques are in good agreement except for where there is instability in the flow. For second moment quantities the comparisons were less agreeable. This suggests that the PIV technique has sufficient temporal and spatial resolution to estimate mean velocity depending on the degree of instability in the flow and also provides sufficient images needed to duplicate mean flow but not for higher moment turbulence quantities such as maximum turbulent shear stress. © 2000 Biomedical Engineering Society. PAC00: 8719Uv, 4262Be, 8780-y     

Numerical study of turbulent blood flow through a caged-ball prosthetic heart valve using a boundary-fitted co-ordinate system

A numerical model is developed for steady turbulent flow through a fully open Starr-Edwards caged-ball prosthetic heart valve in the aortic position. An orthogonal boundary-fitted co-ordinate system is generated for the axisymmetric flow domain in the vicinity of the valve. The boundary lines follow the left ventricular wall, an idealised sinus, the aortic wall, and the ball occluder. The governing partial differentiation equations, written in a stream function-vorticity formulation, are recast into their curvilinear equivalents before being discretised into finite-difference equations. The equations are then solved iteratively. Regions of separated flow and elevated fluid stress are identified at several flow rates. Analysis of the numerical solutions reveals a simple power-law relationship between the computed turbulent shear stress and the steady flow rate at important flow field locations. The maximum turbulent shear stress occurs consistently near the sewing-ring tip. However, the peak turbulent shear stress in the sinus separation zone is observed to increase significantly with higher flow rates, exceeding values in many other regions. The numerical solutions compare satisfactorily with experimental measurements.     

Shear stress investigation across mechanical heart valve

The particle image velocimetry technique was used to study the shear field across a transparent mechanical heart valve model in one cardiac cycle. Shear stress was continuously increased until peak systole and high turbulent stress was observed at the orifice of the central channel and also around the occluder trailing tips. The peak Reynolds shear stress was up to 500 N/m at peak systole, which was higher than the normal threshold for hemolysis.     

Turbulence characteristics downstream of a new trileaflet mechanical heart valve

Design limitations of current mechanical heart valves cause blood flow to separate at the leaflet edges and annular valve base, forming downstream vortex mixing and high turbulent shear stresses. The closing behavior of a bileaflet valve is associated with reverse flow and may lead to cavitation phenomenon. The new trileaflet (TRI) design opens similar to a physiologic valve with central flow and closes primarily due to the vortices in the aortic sinus. In this study, we measured the St. Jude Medical 27 mm and the TRI 27 mm valves in the aortic position of a pulsatile circulatory mock loop under physiologic conditions with digital particle image velocimetry (DPIV). Our results showed the major principal Reynolds shear stresses were <100 N/m2 for both valves, and turbulent viscous shear stresses were smaller than 15 N/m2. The TRI valve closed more slowly than the St. Jude Medical valve. As the magnitudes of the shear stresses were similar, the closing velocity of the valves should be considered as an important factor and might reduce the risks of thrombosis and thromboembolism.     

Effect of oscillation on elevating shear stresses

The effect of oscillation on elevating turbulent shear stresses through the Jellyfish and St. Vincent valves has been investigated. Laser Doppler anemometry was employed to determine the velocity and shear stress distributions at various locations downstream of the valves. Comparison between two valves revealed that at 0.5D downstream of the valves the magnitude of shear stresses in the Jellyfish valve were much higher than those of the St. Vincent valve at cardiac outputs of 4, 5.5 and 7 l min^?1. The cause of high shear stresses in close proximity to the Jellyfish valve could be attributed to the oscillation of the membrane which in turn generated a wake downstream of the valve (in the core of valve chamber) and produced a wide region of disturbance further downstream. This resulted in further pressure drag, and consequently higher pressure drops across the valve and higher shear stresses downstream of the valve.     

An experimental study of steady flow patterns of a new trileaflet mechanical aortic valve

Hemodynamic research shows that thrombosis formation is closely tied to flow field turbulent stress. Design limitations cause flow separation at leaflet edges and the annular valve base, vortex mixing downstream, and high turbulent shear stress. The trileaflet design opens like a physiologic valve with central flow. Leaflet curvature approximates a completely circular orifice, maximizing effective flow area of the open valve. Semicircular aortic sinuses downstream of the valve allow vortex formation to help leaflet closure. The new trileaflet design was hemodynamically evaluated via digital particle image velocimetry and laser-Doppler anemometry. Measurements were made during peak flow of the fully open valve, immediately downstream of the valve, and compared with the 27-mm St. Jude Medical (SJM) bileaflet valve. The trileaflet valve central flow produces sufficient pressure to inhibit separation shear layers. Absence of downstream turbulent wake eddies indicates smooth, physiologic blood flow. In contrast, SJM produces strong turbulence because of unsteady separated shear layers where the jet flow meets the aortic sinus wall, resulting in higher turbulent shear stresses detrimental to blood cells. The trileaflet valve simulates the physiologic valve better than previous designs, produces smoother flow, and allows large scale recirculation in the aortic sinuses to help valve closure.     

Mathematical mdoel for turbulent blood flow through a disk-type prosthetic heart valve

Computational fluid dynamic techniques are used to construct a mathematical model for turbulent blood flow through a disk-type prosthetic heart valve in the aortic position. The TEACH computer code is used to solve the k-6 turbulence model numerically over the axisymmetric flow field of the valve during systole. Stream function, mean axial velocity profiles, turbulent shear stresses and wall shear stress distributions are computed for Reynolds numbers between Re_D=600 and 10 000 (corresponding to steady flow rates of 2·63 lmin⁻¹ and 43·89lmin⁻¹, respectively). The location, length and maximum reverse flow velocities of separated, flow regions are presented and compared with experimental observations. The largest computed mean axial velocities are 4·4 to 4·8 times the inflow velocity and occur near the downstream corner of the sewing ring. The maximum wall shear stress computed is 229·7 Nm⁻² at the upstream corner of the disk occluder for Re_D=10000. The location of maximum walls shear stress occurs at the downstream corner of the sewing ring for Re_D≤2000. Turbulent shear stresses of up to 380·7 Nm⁻² are computed in the region between the sewing ring and the disk occluder for the physiological Reynolds number Re_D=6054. The numerical solutions are shown to compare favourably with available experimental measurements.     

Velocity and shear stress distribution downstream of mechanical heart valves in pulsatile flow

Ten mechanical valves (TAD 27 mm): Starr-Edwards Silastic Ball, Bj?rk-Shiley Standard, Bj?rk-Shiley Concave-Convex, Bj?rk-Shiley Monostrut, Hall-Kaster (Medtronic-Hall), OmniCarbon, Bicer Val, Sorin, Saint-Jude Medical and Hemex (Duromedics) are investigated in a comparative in vitro study. The velocity and turbulent shear stress profiles of the valves were determined by Laser Doppler anemometry in two different downstream axes within a model aortic root. Depending on the individual valve design, velocity peaks up to 1.5 m/s and turbulent shear stress peaks up to 150 N/m2 were measured during the systolic phase. These shear stress peaks mainly occurred in areas of flow separation and intense momentum exchange. Directly downstream of the valves (measuring axis 0.55.dAorta) turbulent shear stress peaks occurred at peak systole and during the deceleration phase, while in the second measuring axis (1.5.dAorta) turbulence levels were lower. Shear stress levels were high at the borders of the fluid jets. The results are discussed from a fluid-dynamic point of view.