On Generation of Tonal Sound Vibrations by Airflow in Stenotic Airways.

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-obstacle type. A stenosis forming a high-speed jet plays the role of a nozzle in the act of breathing. The other stenosis, bifurcation of the airways or the sputum formations can play the role of an obstacle. An experimental installation was used to check the mentioned hypothesis. It included a physical model of an airway along with the equipment for recording and processing of the sound .signals and for 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 vibrations, which spectra are very similar to those of wheezes. A number of laws, being characteristic for the considered structures, is established. The threshold values of flow velocities when the tonal sound vibrations start to arise are estimated. It is shown that the relative distance between a stenosis forming a jet and an obstacle being increased, the threshold Reynolds numbers and the threshold frequencies of the tonal signals tend to a decrease, and the threshold Strouhal numbers - to an increase. [ABSTRACT FROM AUTHOR]