Sound transmission in the lung as a function of lung volume

J Appl Physiol (1985). 2002 Aug;93(2):667-74. doi: 10.1152/japplphysiol.00050.2002.

Abstract

We were interested in how the transmission of sound through the lung was affected by varying air content in intact humans as a method of monitoring tissue properties noninvasively. To study this, we developed a method of measuring transthoracic sound transit time accurately. We introduced a "coded" sound at the mouth and measured the transit time at multiple microphones placed over the chest wall by using a 16-channel lung sound analyzer (Stethographics). We used a microphone placed over the neck near the trachea as our reference and utilized cross-correlation analysis to calculate the transit times. The use of the coded sound, composed of a mix of frequencies from 130 to 150 Hz, greatly reduced the ambiguity of the cross-correlation function. The measured transit time varied from 1 ms at the central locations to 5 ms at the lung bases. Our results also indicated that transit time at all locations decreased with increasing lung volume. We found that these results can be described in terms of a model in which sound transmission through the lung is treated as a combination of free-space propagation through the trachea and a propagation through a two-phase system in the parenchyma.

MeSH terms

  • Acoustics*
  • Adult
  • Aged
  • Computer Simulation
  • Female
  • Humans
  • Lung / physiology*
  • Lung Volume Measurements*
  • Male
  • Middle Aged
  • Models, Biological*
  • Sound