Dynamics of pulsed-ultrasound driven gas-liquid interfaces

Abstract

Pulsed ultrasound has been shown to be capable of inducing lung hemorrhage in mammals, though the physical mechanism remains unknown. We model ultrasound-alveolar interactions as a compressible fluid system and perform numerical experiments to investigate the relevant dynamics. Previously we demonstrated that the interaction between trapezoidal acoustic waves and perturbed gas-liquid interfaces, such as those in the lung, can generate sufficient baroclinic vorticity to appreciably deform the interface under certain conditions. In this work we study the dynamics of perturbed liquid-gas interfaces driven by a single ultrasound pulse in and out of the clinically relevant range with frequencies 1.5-3 MHz and amplitudes 1-15 MPa. We calculate theoretical stresses and strains and compare to established failure criteria. We observe that for ultrasound pulses that significantly deform the interface during the wave-interface interaction, there is residual vorticity left at the interface which can deform the interface long after the passage of the wave. This effect increases with wave amplitude, pulse duration, and initial interface perturbation amplitude. Previously presented scaling laws for the interface perturbation amplitude and arc length growth are tested. While we find that nominal interface strains greater than 1 occur we recognize that the applicability of this study to diagnostic lung ultrasound is limited by the accuracy of the model.