Influence of inhomogeneity and geometry on lung response to low-frequency underwater sound

Abstract

An effective medium, finite-element model has been developed for human lung response to low-frequency underwater sound [Wochner et al., J. Acoust. Soc. Am. 121, 3082 (2007)]. Macroscopic properties are determined by averaging over microscopic properties associated with lung tissue elasticity and alveolar geometry. The resulting elastic constants depend on lung volume, and thus vary with the phase of the breathing cycle. This presentation discusses effects due to spatial variations in lung and geometric features specific to the anatomy of lung. An important variation in elastic properties occurs where soft tissue of the parenchyma attaches to much stiffer bronchial tissue, resulting in stresses that may cause injury at high levels of acoustic excitation. A factor affecting inhomogeneity within the parenchyma is the orientation of the swimmer. When vertical, the suspension of the lung under its own weight may cause the stiffness to be higher at the top of the lung than at the bottom, resulting in a change in the lung resonance frequency. Finally, patient-specific geometries based on volumetric data of the human thorax are considered. Results will be presented showing stress and strain fields, lung resonance, and mode shapes. [Work supported by ONR and ARL:UT IR&D.]