Vortex formation time: an emerging echocardiographic index of left ventricular filling efficiency?
Vortex formation time: an emerging echocardiographic index of left ventricular filling efficiency?
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涡流形成时间：左心室充盈效率的新兴超声心动图指标？
DOI：
10.1093/ejechocard/jer311
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
Belohlavek,Marek
中科院分区：
文献类型：
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作者：
Belohlavek,Marek
大约500年前，列奥纳多·达·芬奇对瓦尔萨尔瓦的鼻窦进行了血液动力学研究，他在研究中推断并解释了血液流动漩涡的形成。2快进到现在，Gharib等人。1使用了一种活塞的实验装置，通过将长度为L的流体柱推过直径为D的小孔，在这些射流旁边产生各种射流和涡环。他们将长径比，即L/D称为形成数。当设置较低的L/D时，只产生一个较弱的涡环，而设置较大的L/D时，会产生一个不再增长的涡环，紧随其后的是尾随喷流的低效流体传输。3在较宽的流动条件下，当L/D比在3.6~4.6时，没有尾随射流的涡环生长最大。1因为L可以用平均活塞速度(U)和活塞行程持续时间(T)来表示为L=U×t，所以编队数可以定义为L/D=U×t/D。1方程的右侧包含了时间信息，解释了为什么这个无量纲指标也被称为涡流形成时间。Poh等人。4报道正常人及有无左室射血分数(EF)保留的心力衰竭患者的VFT值。在排除标准的基础上，研究中只使用了没有重大原发瓣膜疾病的受试者的数据，这一点很重要，因为二尖瓣病变会削弱瓣膜运动学和旋涡限制形成时间之间的相关性。5本研究结果提示VFT可作为预测心力衰竭患者不良心血管事件的指标。正如作者所说，VFT是一个综合指标，其组成部分参数的预后意义已被证实。然而，“整体”，即VFT作为综合指数，在某些方面可能比其组成部分的组合更好：实验证据表明，最佳VFT值的狭窄范围可能代表有效涡环形成的普遍时间尺度。1此外，舒张期涡环似乎起到临时动能储存器5、6的作用，在射血前阶段7、8期间支持血液重定向到流出道，并产生启动二尖瓣及时关闭的力。9然后，人们可以推测，例如，舒张期涡旋的形成(或缺乏)是与心脏再同步化治疗后左心功能或临床状态改善(或无改善)有关的脑室内流体动力学因素。在这方面，Sengupta等人的一项实验研究。7文献表明，在射血前期，从窦性心律转变为左心外膜或右心房起搏会导致组织良好的旋涡消失，并出现血液湍流。另一项不同的实验研究表明，LV后负荷的急性升高导致平均VFT值显著下降，低于最佳范围。图1基于超声心动图粒子图像测速仪11-14，应用于本实验研究中收集的对比度剪辑10在基线和中等左心室后负荷期间。新出现的超声心动图成像方法补充了VFT参数分析，使涡环的损失在视觉上是明显的，并提供了局部血流速度矢量。Poh等人目前的研究。此外，VFT可以将对照受试者与EF保留的HF患者以及EF保留的HF患者与…患者区分开来
About 500 years ago, Leonardo da Vinci conducted a haemodynamic study of the sinus of Valsalva in which he deduced and explained formation of a blood flow vortex. 2 Fast forwarding to the present, Gharib et al. 1 used an experimental arrangement of a piston producing a wide range of jets and vortex rings alongside those jets by pushing columns of fluid of length L through an orifice with diameter D. They referred to the length-to-diameter ratio, ie L/D, as the formation number. While settings with low L/D generated merely a single and rather weak vortex ring, settings with large L/D resulted in a vortex ring that could no longer grow and was followed by a less-efficient fluid transport by a trailing jet. 3 The maximum growth of the vortex ring without a trailing jet was observed when the L/D ratio was within a limited value range of 3.6–4.6 for an otherwise wide variety of flow conditions. 1 Because L can be expressed in terms of the mean piston velocity (U) and duration of the piston stroke (t) as L= U× t, then the formation number can be defined as L/D= U× t/D. 1 The right side of the equation, which incorporates time information, makes it clear why this dimensionless index is also referred to as vortex formation time (VFT). Poh et al. 4 report VFT values for normal subjects as well as heart failure (HF) patients with and without preserved left ventricular (LV) ejection fraction (EF). On the basis of exclusion criteria, only data from subjects without significant primary valvular disease were used in the study, which is important because mitral pathology would impair correlation between valve kinematics and vortex-limiting formation time. 5 The results of the current study indicate that VFT could be a predictor of adverse cardiovascular events in patients with HF. As the authors state, VFT is a composite index and prognostic significance of its component parameters has previously been demonstrated. However, the ‘whole’, ie VFT as the composite index, may be in some respect better than the combination of its component parts: experimental evidence suggests that the narrow range of optimal VFT values may represent a universal time scale for efficient vortex ring formation. 1 Moreover, a diastolic vortex ring appears to function as a temporary kinetic energy reservoir 5, 6 that supports blood redirection into the outflow tract during the preejection phase 7, 8 and generates a force that initiates timely closure of the mitral valve. 9 One could then speculate that, for example, formation of a diastolic vortex (or lack thereof) is an intraventricular fluid dynamics factor associated with improvement (or no improvement) of LV function or clinical status after cardiac resynchronization therapy. In this context, an experimental study by Sengupta et al. 7 documents that conversion from a sinus rhythm to LV epicardial or right atrial pacing results in loss of a well-organized vortex and occurrence of blood turbulence during the preejection period. A different experimental study, 10 in which measurement of D reflected early diastolic filling, demonstrates that acute elevation of LV afterload leads to a significant drop of the mean VFT value below the optimal range. Figure 1 is based on echocardiographic particle image velocimetry 11–14 applied to contrast clips collected in this experimental study 10 at baseline and during moderate LV afterload. The emerging echocardiographic imaging method complements the VFT parametric analysis by making loss of a vortex ring visually evident and providing local flow velocity vectors. The current study by Poh et al. also demonstrates that VFT can separate control subjects from HF patients with preserved EF and HF patients with preserved EF from those with …