Source: Annual Congress 2002 - Airway obstruction measurement (FOT - NEP) sleep and lung sound analysis

Abstract

Background and Purpose: The speed of sound in the lung changes with changing tissue properties and thus measurement of sound speed has the potential to help in non-invasive diagnosis. Introduction of sound at the mouth for this purpose can be difficult in certain clinical situations such as in the comatose or intubated patient. Accordingly we were interested in a method of measurement speed of sound in the lungs that avoided this problem.
Methods: We introduced a sound, composed of a mix of frequencies from 70Hz to 140Hz, at the supraclavicular space and measured the transit time at multiple microphones placed over the chest wall using a 16 channel lung sound analyzer (Stethographics, Model STG1602). We used the microphone placed next to the speaker as our reference and utilized cross correlation analysis to calculate the transfer times. The sound was [dsquote]coded[dsquote] sound, greatly reducing the ambiguity of the crosscorrelation function. In addition, the introduction of sound in the supraclavicular space reduced the problem of sound transmission through bone.
Results: The measured transit time varied from 6ms at the central locations to 14ms at the lung bases. This transit time corresponds to the speed of sound of around 25m/s. This approximation is similar to the speed of sound in the lung parenchyma when test sound is input at the mouth. 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 the lung is treated as a two-phase system.
Conclusion: Injection of sound into the supraclavicular space allows sound speed measurements in patients unable to cooperate with input of sound at the mouth and provides similar results.
Stethographics, Inc., ERS 2002

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Citations should be made in the following way:
R. Murphy, A. Vyshedskiy, J. Shane, D. Bana (Boston, United States Of America). Sound speed in the lung measured by sound injection into supraclavicular space. Eur Respir J 2002; 20: Suppl. 38, 323

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