Ali Ahmed M, Hafez Ahmed H, Elkhodary Khalil I, El-Morsi Mohamed
Department of Mechanical Engineering, The American University in Cairo, 11835 New Cairo, Egypt.
Aerospace Engineering Department, Cairo University, 12511 Giza, Egypt.
Heliyon. 2023 Jun 29;9(7):e17643. doi: 10.1016/j.heliyon.2023.e17643. eCollection 2023 Jul.
In this paper, we identify a new (acoustic) frequency-stenosis relation whose frequencies lie within the recommended auscultation threshold of stethoscopy (< 120 Hz). We show that this relation can be used to extend the application of phonoangiography (quantifying the degree of stenosis from bruits) to widely accessible stethoscopes. The relation is successfully identified from an analysis restricted to the acoustic signature of the von Karman vortex street, which we automatically single out by means of a metric we propose that is based on an area-weighted average of the Q-criterion for the post-stenotic region. Specifically, we perform CFD simulations on internal flow geometries that represent stenotic blood vessels of different severities. We then extract their emitted acoustic signals using the Ffowcs Williams-Hawkings equation, which we subtract from a clean signal (stenosis free) at the same heart rate. Next, we transform this differential signal to the frequency domain and carefully classify its acoustic signatures per six (stenosis-)invariant flow phases of a cardiac cycle that are newly identified in this paper. We then automatically restrict our acoustic analysis to the sounds emitted by the von Karman vortex street (phase 4) by means of our Q-criterion-based metric. Our analysis of its acoustic signature reveals a strong linear relationship between the degree of stenosis and its dominant frequency, which differs considerably from the break frequency and the heart rate (known dominant frequencies in the literature). Applying our new relation to available stethoscopic data, we find that its predictions are consistent with clinical assessment. Our finding of this linear correlation is also unlike prevalent scaling laws in the literature, which feature a small exponent (i.e., low stenosis percentage sensitivity over much of the clinical range). They hence can only distinguish mild, moderate, and severe cases. Conversely, our linear law can identify variations in the degree of stenosis sensitively and accurately for the full clinical range, thus significantly improving the utility of the relevant scaling laws... Future research will investigate incorporating the vibroacoustic role of adjacent organs to expand the clinical applicability of our findings. Extending our approach to more complex 3D stenotic morphologies and including the vibroacoustic role of surrounding organs will be explored in future research to advance the clinical reach of our findings.
在本文中，我们识别出一种新的（声学）频率-狭窄关系，其频率位于听诊器推荐的听诊阈值范围内（<120Hz）。我们表明，这种关系可用于将血管音图（从杂音量化狭窄程度）的应用扩展到广泛使用的听诊器。该关系是通过对仅局限于冯·卡门涡街声学特征的分析成功识别出来的，我们通过一种基于狭窄后区域Q准则的面积加权平均值所提出的度量标准自动挑选出该声学特征。具体而言，我们对代表不同严重程度狭窄血管的内部流动几何结构进行计算流体动力学（CFD）模拟。然后，我们使用Ffowcs Williams-Hawkings方程提取它们发出的声学信号，并从相同心率下的干净信号（无狭窄）中减去该信号。接下来，我们将这个差分信号转换到频域，并根据本文新识别出的心动周期的六个（与狭窄相关的）不变流动阶段仔细分类其声学特征。然后，我们借助基于Q准则的度量标准自动将声学分析局限于冯·卡门涡街发出的声音（阶段4）。我们对其声学特征的分析揭示了狭窄程度与其主导频率之间存在很强的线性关系，这与转折频率和心率（文献中已知的主导频率）有很大不同。将我们的新关系应用于现有的听诊数据，我们发现其预测与临床评估一致。我们发现的这种线性相关性也不同于文献中普遍存在的标度律，后者的指数较小（即，在大部分临床范围内对狭窄百分比的敏感度较低）。因此，它们只能区分轻度、中度和重度病例。相反，我们的线性定律能够在整个临床范围内灵敏且准确地识别狭窄程度的变化，从而显著提高相关标度律的实用性……未来的研究将探讨纳入相邻器官的振动声学作用，以扩大我们研究结果的临床适用性。未来的研究将探索将我们的方法扩展到更复杂的三维狭窄形态，并纳入周围器官的振动声学作用，以推进我们研究结果的临床应用范围。
