Sound transmission in the lung as a function of lung volume.
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.
Bergstresser
T
T
University of Massachusetts, Boston, Massachussetts 02130, USA.
Ofengeim
D
D
Vyshedskiy
A
A
Shane
J
J
Murphy
R
R
D000162:Acoustics; D000328:Adult; D000368:Aged; D003198:Computer Simulation; D005260:Female; D006801:Humans; D008168:Lung / Q000502:physiology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D013016:Sound