Simulation of bronchial airway acoustics in healthy and asthmatic subjects

The onset and development of many airway pathologies affect sound propagation throughout the respiratory system; changes in respiratory sounds are detected primarily by auscultation, which is highly skill dependent. The aim of the present study was to compare healthy and asthmatic pulmonary acoustics by applying a 1D model of wave propagation on CT-based patient-specific geometries. High-resolution CT lung images were acquired in five healthy volunteers and five asthmatic patients at total lung capacity (TLC) and functional residual capacity (FRC). Tracheobronchial trees were reconstructed from CT images. Acoustic pressure, impedance and wall radial velocity were measured by simulating acoustic wave propagation of two external, acoustic pressure waves (1 Pa, 200 and 600 Hz) from the trachea level to the 4th generation. In asthmatic patients, acoustic pressure averaged across the last three generations showed a reduction equal to 29.7% (p<0.01) at FRC, at 200 Hz; input and terminal impedance were 34.5% (p<0.05) higher both at FRC and TLC; wall radial velocity was more than 80% (p<0.05) lower in higher generations both at FRC and TLC. Airway differences in asthma alter acoustic parameters at FRC and TLC, with the greatest difference at FRC and 200 Hz. Acoustic wave propagation analysis represents a quantitative approach that has potential to objectively characterize airway differences in individuals with diseases such as asthma.

多种气道疾病的发生与发展均会影响声波在呼吸系统内的传播；呼吸音的改变主要通过听诊（auscultation）进行检测，但该检测方式高度依赖操作者的专业技能。本研究旨在基于患者个体的计算机断层扫描（Computed Tomography, CT）几何模型，通过一维声波传播模型，对比健康人群与哮喘患者的肺部声学特性。本研究招募5名健康志愿者与5名哮喘患者，分别在肺总量（total lung capacity, TLC）与功能残气量（functional residual capacity, FRC）状态下采集其高分辨率CT肺部图像。研究人员从CT图像中重建出气管支气管树模型。通过模拟从气管水平至气道第4代分支的两种外部声压波（1 Pa，频率分别为200 Hz与600 Hz）的传播过程，测量了声压、声阻抗（acoustic impedance）以及气道壁径向速度。在哮喘患者中，于功能残气量状态下、200 Hz频率时，气道最后3代分支的平均声压下降了29.7%（p<0.01）；其输入声阻抗与终端声阻抗在肺总量与功能残气量状态下均升高了34.5%（p<0.05）；气道壁径向速度在功能残气量与肺总量状态下的较高级气道分支中均降低了80%以上（p<0.05）。哮喘引发的气道结构差异会改变肺总量与功能残气量状态下的声学参数，其中以功能残气量状态下200 Hz频率时的差异最为显著。声波传播分析作为一种定量分析方法，有望客观表征哮喘等疾病患者的气道结构差异。