Pulmonary diseases and injury lead to structural and functional changes in the lung parenchyma and airways, often resulting in measurable sound transmission changes on the chest wall surface. Additionally, noninvasive imaging of externally driven mechanical wave motion in the chest (e.g., using magnetic resonance elastography) can provide information about lung stiffness and other structural property changes which may be of diagnostic value. In the present study, a comprehensive computational simulation (in silico) model was developed to simulate sound wave propagation in the airways, parenchyma, and chest wall under normal and pathological conditions that create distributed structural (e.g., pneumothoraces) and diffuse material (e.g., fibrosis) changes, as well as a localized structural and material changes as may be seen with a neoplasm. Experiments were carried out in normal subjects to validate the baseline model. Sound waves with frequency content from 50 to 600 Hz were introduced into the airways of three healthy human subjects through the mouth, and transthoracic transmitted waves were measured by scanning laser Doppler vibrometry at the chest wall surface. The computational model predictions of a frequency-dependent decreased sound transmission due to pneumothorax were consistent with experimental measurements reported in previous work. Predictions for the case of fibrosis show that while shear wave motion is altered, changes to compression wave propagation are negligible, and thus, insonification, which primarily drives compression waves, is not ideal to detect the presence of fibrosis. Results from the numerical simulation of a tumor show an increase in the wavelength of propagating waves in the immediate vicinity of the tumor region.

Graphical abstract

肺部疾病和损伤导致肺实质和气道的结构和功能变化，通常导致胸壁表面可测量的声音传输变化。另外，胸部中外部驱动的机械波运动的无创成像（例如，使用磁共振弹性成像）可以提供关于肺硬度和可能具有诊断价值的其他结构特性变化的信息。在本研究中，开发了一个综合计算模拟（计算机）模型来模拟正常和病理条件下声波在气道、实质和胸壁中的传播，从而产生分布式结构（例如，气胸）和弥散物质（例如，纤维化）变化，以及局部结构和材料的变化，如肿瘤所示。在正常受试者中进行实验以验证基线模型。将频率为 50 至 600 Hz 的声波通过口腔引入三名健康受试者的气道，并通过扫描激光多普勒测振法​​在胸壁表面测量经胸透射波。由于气胸而导致的频率依赖性声音传输减少的计算模型预测与先前工作中报告的实验测量结果一致。对纤维化情况的预测表明，虽然剪切波运动发生了改变，但压缩波传播的变化可以忽略不计，因此，主要驱动压缩波的声穿透对于检测纤维化的存在并不理想。肿瘤数值模拟的结果显示，紧邻肿瘤区域的传播波的波长增加。

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