Measurements of lung vibration in response to low-frequency sound

Abstract

The amplitude of vibration of lung in response to low-frequency (100–500 Hz) sound was measured in mice and rats in vivo. Low-frequency sound fields were generated in an inertial water column driven at its base with an electromagnetic transducer. Estimates of vibration amplitude of the lung were obtained by calculating the variations in the round-trip delay of pulsed wideband ultrasound bursts. The relative time delays were calculated by determining the maximum of the cross-correlation of the first echo with subsequent echoes. The ultrasound bursts were emitted at a rate of 1–5 kHz, allowing ten displacement estimates to be calculated per cycle of lung oscillation. The mean resonance frequencies obtained through measurements of vibration amplitude were 330 Hz for mice and 189 Hz for rats. The maximum observed displacements were on the order of 0.1 mm. The resonance observed through measurements of displacement amplitude was equivalent to that obtained through acoustic scattering measurements and consistent with observations of lung hemorrhage.