Auscultation has been used qualitatively by physicians for hundreds of years to aid in the monitoring and diagnosis of pulmonary diseases. Alterations in the structure and function of the pulmonary system that occur in disease or injury often give rise to measurable changes in lung sound production and transmission. Numerous acoustic measurements have revealed the differences of breath sounds and transmitted sounds in the lung under normal and pathological conditions. Compared to the extensive cataloging of lung sound measurements, the mechanism of sound transmission in the pulmonary system and how it changes with alterations of lung structural and material properties has received less attention. A better understanding of sound transmission and how it is altered by injury and disease might improve interpretation of lung sound measurements, including new lung imaging modalities that are based on an array measurement of the acoustic field on the torso surface via contact sensors or are based on a 3-dimensional measurement of the acoustic field throughout the lungs and torso using magnetic resonance elastography.;A long-term goal of the Audible Human Project (AHP ) is to develop a computational acoustic model that would accurately simulate generation, transmission and noninvasive measurement of sound and vibration within the pulmonary system and torso caused by both internal (e.g. respiratory function) and external (e.g. palpation) sources. The goals of this dissertation research, fitting within the scope of the AHP, are to develop specific improved theoretical understandings, computational algorithms and experimental methods aimed at transmission and measurement. The research objectives undertaken in this dissertation are as follows. (1) Improve theoretical modeling and experimental identification of viscoelasticity in soft biological tissues. (2) Develop a poroviscoelastic model for lung tissue vibroacoustics. (3) Improve lung airway acoustics modeling and its coupling to the lung parenchyma; and (4) Develop improved techniques in array acoustic measurement on the torso surface of sound transmitted through the pulmonary system and torso.;Tissue Viscoelasticity. Two experimental identification approaches of shear viscoelasticity were used. The first approach is to directly estimate the frequency-dependent surface wave speed and then to optimize the coefficients in an assumed viscoelastic model type. The second approach is to measure the complex-valued frequency response function (FRF) between the excitation location and points at known radial distances. The FRF has embedded in it frequency-dependent information about both surface wave phase speed and attenuation that can be used to directly estimate the complex shear modulus. The coefficients in an assumed viscoelastic tissue model type can then be optimized.;Poroviscoelasticity Model for Lung Vibro-acoustics. A poroviscoelastic model based on Biot theory of wave propagation in porous media was used for compression waves in the lungs. This model predicts a fast compression wave speed close to the one predicted by the effective medium theory at low frequencies and an additional slow compression wave due to the out of phase motion of the air and the lung parenchyma. Both compression wave speeds vary with frequency. The fast compression wave speed and attenuation were measured on an excised pig lung under two different transpulmonary pressures. Good agreement was achieved between the experimental observation and theoretical predictions.;Sound Transmission in Airways and Coupling to Lung Parenchyma. A computer generated airway tree was simplified to 255 segments and integrated into the lung geometry from the Visible Human Male for numerical simulations. Acoustic impedance boundary conditions were applied at the ends of the terminal segments to represent the unmodeled downstream airway segments. Experiments were also carried out on a preserved pig lung and similar trends of lung surface velocity distribution were observed between the experiments and simulations. This approach provides a feasible way of simplifying the airway tree and greatly reduces the computation time.;Acoustic Measurements of Sound Transmission in Human Subjects. Scanning laser Doppler vibrometry (SLDV) was used as a gold standard for transmitted sound measurements on a human subject. A low cost piezodisk sensor array was also constructed as an alternative to SLDV. The advantages and disadvantages of each technique are discussed.
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机译：听诊已被医师定性使用了数百年，以帮助监测和诊断肺部疾病。在疾病或伤害中发生的肺系统结构和功能的改变通常会导致可测量的肺音产生和传播变化。在正常和病理条件下，许多声学测量已揭示出呼吸声和肺部传播声的差异。与广泛的肺部声音测量分类相比，肺部系统中声音传输的机制以及其随着肺部结构和材料特性的变化而发生的变化受到的关注较少。更好地了解声音的传输以及如何通过伤害和疾病改变声音的传输可能会改善对肺部声音测量的解释，包括基于接触传感器对躯干表面声场进行阵列测量或基于使用磁共振弹性成像技术对整个肺部和躯干中的声场进行3维测量; Audible Human Project（AHP）的长期目标是开发一种可精确模拟生成，传输和无创测量的计算声学模型内部（例如呼吸功能）和外部（例如触诊）来源引起的肺系统和躯干内的声音和振动的变化。本论文研究的目的是在AHP的范围内，以发展针对传输和测量的特定改进的理论理解，计算算法和实验方法。本文的研究目标如下。 （1）改进生物软组织粘弹性的理论模型和实验鉴定。 （2）建立肺组织振动声学的黏弹性模型。 （3）改善肺气道声学模型及其与肺实质的耦合； （4）开发改进的技术，对通过肺系统和躯干传播的声音在躯干表面进行阵列声学测量。组织粘弹性。使用了两种剪切粘弹性的实验识别方法。第一种方法是直接估计与频率相关的表面波速度，然后在假定的粘弹性模型类型中优化系数。第二种方法是测量激励位置和已知径向距离的点之间的复数值频率响应函数（FRF）。 FRF在其中嵌入了与频率有关的有关表面波相速度和衰减的信息，这些信息可用于直接估计复数剪切模量。然后可以优化假定的粘弹性组织模型类型中的系数。肺部声学声学的多孔弹性模型。基于Biot理论的多孔流体在多孔介质中传播的多孔弹性模型用于压缩肺中的波浪。该模型预测的低频快速压缩波速度接近有效介质理论所预测的速度，而由于空气和肺实质的异相运动，将产生另外的缓慢压缩波。两种压缩波的速度都随频率而变化。在两个不同的经肺压力下，在切除的猪肺上测量快速压缩波的速度和衰减。在实验观察和理论预测之间取得了良好的一致性。气道中的声音传播和肺实质的耦合。将计算机生成的气道树简化为255段，并从“可见人类”中将其集成到肺部几何结构中以进行数值模拟。在终端段的末端施加声阻抗边界条件，以代表未建模的下游气道段。还对保存的猪肺进行了实验，在实验和模拟之间观察到了相似的肺表面速度分布趋势。这种方法为简化气道树提供了可行的方法，并大大减少了计算时间。人体中声音传输的声学测量。扫描激光多普勒振动法（SLDV）被用作在人体上传输声音的金标准。还构造了低成本的压电磁盘传感器阵列，以替代SLDV。讨论了每种技术的优缺点。
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