Potential relationships among myocardial stiffness, the measured level of myocardial backscatter ("image brightness"), and the magnitude of the systematic variation of backscatter (cyclic variation) over the heart cycle
Potential relationships among myocardial stiffness, the measured level of myocardial backscatter ("image brightness"), and the magnitude of the systematic variation of backscatter (cyclic variation) over the heart cycle
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DOI：
10.1016/j.echo.2004.06.004
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发表时间：
2004-11-01
影响因子：
6.5
通讯作者：
Miller, JG
中科院分区：
文献类型：
--
作者：
Holland, MR;Wallace, KD;Miller, JG
背景：在最近发表的一些比较患者和对照组的研究中，当在心脏周期的特定阶段(例如，收缩末期或舒张末)测量时，心脏周期内背向散射能量的系统变化(周期变化)的幅度减小伴随着整体心肌背向散射水平(校准的心肌图像亮度)的增加。这项研究的目的是调查这一观察结果是否与基于包含心脏周期内和细胞外相对声阻抗变化的周期变化机制模型的预测一致。方法：利用前面描述的代表心脏细胞力学行为的三分量Maxwell类型的肌肉力学模型来预测心脏周期内和细胞外弹性特性之间的相对声阻抗差的系统变化，从而预测所观察到的周期变化的幅度和整体心肌散射水平。获得了一系列细胞内和细胞外相对声阻抗的特定值的预测值。结果：结果表明，预测的周期变化的大小可以直接与整体心肌背向散射水平相关。例如，在不改变细胞内声阻抗的情况下，细胞外基质的声阻抗(刚性特性)的特定变化导致舒张末心肌背向散射水平的预测值为-43.5分贝、-38.5分贝和-33.5分贝，而预测的循环变化幅度的相应值为5.0分贝、2.5分贝和1.3分贝，结论：本研究表明，随着心肌总后向散射水平的增加，所观察到的心肌细胞周期变化幅度的减小与基于细胞内和细胞外弹性特性在心脏周期中的相对声阻抗差异的模型的预测一致。这些结果表明，超声背向散射测量可能为评估心肌僵硬、纤维化程度和收缩性能之间的关系提供了一种非侵入性的方法。
Background: In a number of recently published studies comparing measurements from patients with those from control subjects, a decreased magnitude of the systematic variation of backscattered energy over the heart cycle (cyclic variation) is accompanied by an increased level of overall myocardial backscatter (calibrated myocardial image brightness) when measured at a specific phase of the heart cycle (eg, end systole or end diastole). The goal of this study was to investigate whether this observation is consistent with predictions based on a model of the mechanisms of cyclic variation incorporating changes in relative intracellular and extracellular acoustic impedance over the heart cycle.Methods: A previously described 3-component Maxwell-type model of muscle mechanics representing cardiac cell mechanical behavior was utilized to predict the systematic variation in the relative acoustic impedance differences between intracellular and extracellular elastic properties over the heart cycle and hence the observed magnitude of cyclic variation and overall myocardial scattering level. Predictions were obtained for a series of specific values of relative intracellular and extracellular acoustic impedance.Results: Results indicate that the predicted magnitude of cyclic variation can be directly related to the overall myocardial backscatter level. For example, specific changes in the acoustic impedance (stiffness properties) of the extracellular matrix without any change in the intracellular acoustic impedance result in predicted values of -43.5 dB, -38.5 dB, and -33.5 dB for end-diastolic myocardial backscatter levels with corresponding values of 5.0 dB, 2.5 dB, and 1.3 dB for the predicted magnitude of cyclic variation, respectively.Conclusion: This study suggests that observed decreases in the magnitude of cyclic variation with concomitant increases in the measured overall myocardial backscatter level are consistent with predictions from a model based on the relative acoustic impedance differences between intracellular and extracellular elastic properties over the heart cycle. These results suggest that ultrasonic backscatter measurements may provide a noninvasive approach for assessing some relationships among myocardial stiffness, degree of fibrosis, and contractile performance.