|
背景 心肌僵硬度是影响舒张和收缩心脏功能的心肌的固有特性。心肌僵硬代表该组织对形变的抵抗力，并且取决于心肌细胞的细胞内成分，特别是细胞骨架，以及细胞外成分，例如胶原纤维。心肌病与心肌硬度的变化有关，其评估是急性或慢性病理性心肌病的关键诊断标志物，具有指导治疗决策的潜力。在这篇综述中，我们评估了可用于估计心肌硬度的不同技术，评估它们的优缺点，并讨论潜在的临床应用。 心脏是一个动态器官，能够在空间和时间上以协调的方式收缩和舒张。在心动周期中，心肌细胞会改变其形状；它因肌节产生的主动力而收缩。主动收缩后，心肌恢复其被动配置（不是心肌产生的主动力）。这种从主动状态到被动状态的转变是通过肌节松弛过程实现的，该过程导致肌动蛋白-肌球蛋白键的释放和组织弹性的回弹。心肌在受到外力作用时变形的程度是心脏功能的核心决定因素。这种相互作用可以通过心肌的刚度（例如，施加的应力和随后的变形之间的关系的斜率）或更严格地通过其弹性模量来量化。弹性模量是材料固有的，反映了细胞内和细胞外成分的特性及其相互作用。因此，心肌硬度是心肌细胞水平的病理生理状况和改变、肌动蛋白-肌球蛋白相互作用和细胞外基质组成的重要生物标志物，这有助于心肌的非线性特性。除了被动弹性特性外，还有心肌力学特性动态变化，因为心脏是受外部负荷条件影响的收缩器官。因此，心肌硬度在整个心动周期动态变化，并根据心动周期的时间和生理条件而变化。 存在多种估计心肌硬度的方法。其中包括：(1) 通过体外机械技术对肌原纤维、心肌细胞或肌纤维进行直接刚度分析；(2) 利用剪切应力和刚度之间的联系通过成像技术进行非侵入性估计；(3) 腔室硬度，通过使用导管研究压力-容积环进行有创估计；(4) 计算机技术。本综述的目的是详细说明作为心脏硬度评估基础的物理概念、确定心肌硬度的结构、这些物理概念在诊断测试中的应用，最后是心肌硬度评估在临床实践中的应用。 刚度的定义——物理学的概念 重要的是首先要认识到心脏僵硬评估有两个不同但密切相关的方面。一是评估心室作为血流动力学泵的弹性特性（结构刚度或腔室刚度）；另一个是评估心肌的内在弹性特性（材料硬度或心肌硬度）。心室硬度取决于心肌材料特性（心肌硬度）和心室腔室特性（肌肉量、心室结构和心室几何形状）。根据定义，心室硬度是心室压力相对于心室容积变化的变化 (dP/dV)；即舒张末期压力-容积关系（EDPVR）的斜率。这种关系的斜率，β被称为“心室刚度常数”，并已被许多研究人员用作指示舒张心室特性的手段。
心肌僵硬度的解剖 可以在不同水平上研究心肌僵硬度，从细胞和细胞内水平到完整器官。每个级别都有助于理解心脏的机械性能。
非侵入性技术 Acoustic radiation force impulse imaging（声辐射力脉冲成像） Ultrasound is widely used as an imaging modality. In addition to its ability to propagate several centimeters deep in the tissue, it can also be used to generate mechanical stress on the tissue. To achieve this, part of the ultrasound energy is converted into acoustic radiation force, which mechanically displaces the tissue away from the transducer. Bursts of several hundred microseconds (µs) of focused ultrasound can induce micrometric tissue displacements at the beam focal point. Through measurement of the maximum displacement or the relaxation time, the elastic properties of the medium can be derived. Using pushing beams at several spatial locations, it is possible to map the tissue stiffness. In vitro, acoustic radiation force impulse imaging (ARFI) elasticity mapping of the myocardium was used as a monitoring tool for radiofrequency ablation. However, owing to the limited size of the focal point for each pushing beam, regional stiffness mapping of the beating heart remains challenging with ARFI. Nevertheless, by probing the myocardium at a fixed spatial location, Kakkad and colleagues were able to quantify the dynamic myocardial stiffness along the cardiac cycle, for a given location. Ultrafast ultrasound — shear wave propagations（超快超声—剪切波传播） Ultrafast ultrasound imaging (UUI) is a more recently developed imaging technique with possible important original clinical applications for the assessment of myocardial stiffness. By increasing frame rates to >1,000 frames per second, it has become feasible to observe and analyze very short-lived propagating tissue movements that were undetectable by other imaging techniques. A recent application has been the use of UUI to study shear wave propagation in the myocardium to assess mechanical tissue properties. Different techniques have been proposed using either natural shear waves associated with cardiac mechanical events (such as valve closures) or external shear waves generated by acoustic radiation force . Myocardial stiffness can be assessed from the estimation of the shear wave propagation velocity through the relationship between shear velocity, tissue viscoelastic properties, and stiffness (shear modulus). The shear modulus (µ) is related to the density (ρ) of the material and the shear wave velocity (c): $$\mu = \rho c^2$$ Similarly, sudden changes in chamber pressure, such as those that follow atrial contraction, generate left ventricle (LV) myocardial stretch that propagates from base to apex with a speed proportional to myocardial elasticity. The correlation between myocardial stiffness and this myocardial stretch, using the theory of wave propagation in elastic tubes (Moens–Korteweg equation), deserves further study for diagnostic purposes. 结论
作者介绍
|
|
|
来自： 新用户51602341 > 《心脏》
