Zhu Chi, Seo Jung-Hee, Mittal Rajat
Department of Mechanical Engineering,Johns Hopkins University,3400 N. Charles Street,Baltimore, MD 21218e-mail:
J Biomech Eng. 2019 Apr 1;141(4). doi: 10.1115/1.4042765.
In this study, coupled hemodynamic-acoustic simulations are employed to study the generation and propagation of murmurs associated with aortic stenoses where the aorta with a stenosed aortic valve is modeled as a curved pipe with a constriction near the inlet. The hemodynamics of the poststenotic flow is investigated in detail in our previous numerical study (Zhu et al., 2018, "Computational Modelling and Analysis of Haemodynamics in a Simple Model of Aortic Stenosis," J. Fluid Mech., 851, pp. 23-49). The temporal history of the pressure on the aortic lumen is recorded during the hemodynamic study and used as the murmur source in the acoustic simulations. The thorax is modeled as an elliptic cylinder and the thoracic tissue is assumed to be homogeneous, linear and viscoelastic. A previously developed high-order numerical method that is capable of dealing with immersed bodies is applied in the acoustic simulations. To mimic the clinical practice of auscultation, the sound signals from the epidermal surface are collected. The simulations show that the source of the aortic stenosis murmur is located at the proximal end of the aortic arch and that the sound intensity pattern on the epidermal surface can predict the source location of the murmurs reasonably well. Spectral analysis of the murmur reveals the disconnect between the break frequency obtained from the flow and from the murmur signal. Finally, it is also demonstrated that the source locations can also be predicted by solving an inverse problem using the free-space Green's function. The implications of these results for cardiac auscultation are discussed.
在本研究中，采用血流动力学 - 声学耦合模拟来研究与主动脉狭窄相关的杂音的产生和传播，其中，具有狭窄主动脉瓣的主动脉被建模为入口附近有缩窄的弯曲管道。在我们之前的数值研究中（Zhu等人，2018年，“主动脉狭窄简单模型中的血流动力学计算建模与分析”，《流体力学杂志》，第851卷，第23 - 49页），对狭窄后血流动力学进行了详细研究。在血流动力学研究过程中记录主动脉腔内压力的时间历程，并将其用作声学模拟中的杂音源。胸部被建模为椭圆柱体，并且假设胸部组织是均匀、线性和粘弹性的。在声学模拟中应用了一种先前开发的能够处理沉浸体的高阶数值方法。为了模拟听诊的临床实践，收集来自表皮表面的声音信号。模拟结果表明，主动脉狭窄杂音的声源位于主动脉弓的近端，并且表皮表面的声强模式能够较好地预测杂音的声源位置。杂音的频谱分析揭示了从血流中获得的截止频率与从杂音信号中获得的截止频率之间的差异。最后，还证明了通过使用自由空间格林函数求解反问题也可以预测声源位置。讨论了这些结果对心脏听诊的意义。
