V.G.Basovsky, I.V.Vovk, O.I.Vovk On generation of tonal sound oscillations by airflow in stenosed airway |
Acoustic bulletin, Vol. 6 ¹ 1, (2003) |
| A hypothesis about one of possible mechanisms of occurrence of wheezes (tonal sound signals) in a human bronchial tree at its pathologies is put forward. It is supposed that viscous sputum allocated in affected airways, can form aerodynamic structures of the nozzle-jet-obstruction type. At the act of breathing a stenosis forming a high-speed jet plays the role of a nozzle. The other stenosis, bifurcation of the airways or the sputum formations can play the role of an obstruction. To check the mentioned hypothesis the experimental installation was used. This last included the physical model of an airway along with the equipment for registration and processing of the sound signals and estimation of the airflow velocity. As a result of experiments it was shown that presence of the specified aerodynamic structures can provide an efficient transformation of energy of the stream in airways into energy of the sound fluctuations, which spectra are very similar to the spectra of the wheezes. A number of laws, being characteristic for the considered structures, is established. The threshold values of the flow velocities at which the tonal sound fluctuations start to arise are estimated. It is shown that with increasing the relative distance between a stenosis forming a jet and an obstruction, the threshold Reynolds numbers and the threshold frequencies of the tonal signals tend to decrease, and the threshold Strouhal numbers - to increase. |
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KEY WORDS: dry rales, bronchial tree, stenosis, tonal acoustic vibration, sound generation by flow |
| TEXT LANGUAGE: Russian |