Background: Sound propagation in human respiratory system remains poor studied. High frequency 10 – 750 kHz sound transmission through lung tissues was revealed recently by Rueter et al., 2010. Amplitude of transmission of wideband pulses through lung was found dependent on air volume. Sound speed was estimated being close to 1500 m/s.
The objective is to study sound propagation features including spectral characteristics and sound speed in frequency band of 10-19 kHz by means of convolution technique.
Method: The laboratory installation was developed, which included small vibration source, fed through an amplifier from an output of sound card of laptop, a system of acoustic sensors, connected to analog inputs of 16-channel computer laboratory PowerLab (ADInstruments). Frequency sweep signal 10 – 19 kHz was used. Cross-spectrum and convolution techniques were applied.
Results: We studied 10 healthy volunteers, injecting the signal into right supraclavicular area and recording it in medial and basal chest areas. Maximal amplitude of transmission was observed between 13 and 17 kHz. The inverse dependence of sound transmission to basal lung area on pulmonary air volume (RV, FRC, TLC) was found in a half of group. 2-3 arrivals of sounding signal were commonly found by convolution technique. Their sound speed was estimated mainly between 200 and 500 m/s being at least threefold smaller than found by Reuter et al., 2010. The sound speed was inversely proportional to pulmonary air volume in a half of group. This smaller sound speed results in longitudinal wavelengths of about 1.3 – 3.3 cm (for 15 kHz frequency). Such wavelengths seem to be promising for high resolution visualizing pathologic inhomogeneities in lung tissue.
Conclusions: Revealed features of high-frequency sound propagation may be pertinent for transmission acoustic tomography of human lungs. The study was partially supported by the grant 13-08-00010-a of Russian Foundation for Basic Research.
