A Preliminary Experimental Study on the Sound Generation by Flow Impingement in Branching Airway

Abstract

Auscultation method used for diagnosing the respiratory conditions has been conducted since a long time ago. Nevertheless, lack understanding of the formation and propagation of the sound made auscultation remained a perfunctory method. To understand the sound generation mechanisms, we constructed one-generation T-branch model and a straight tube model to study the importance of flow impingement. All models were prepared in 7 mm and 10 mm major diameter to observe the influence of diameter change. Air of Reynolds numbers between 1,000 and 5,000 calculated at the inlet of the parent tube was flown through the models, and the emitted sounds were recorded. Flow in the upstream region was then disturbed by introducing constriction of 25%, 50% and 75% diameter changes in the parent tube. As results, for the no-constriction case, small increase of the overall sound pressure level (OASPL) for increase of Reynolds number in 7 mm and 10 mm models (straight tube and T-branch models) was observed, however, one-generation T-branch model produced higher sound level compared to the straight tube model. When a constriction was introduced in the parent tube of the models, the OASPL increased in a non-linear relationship for all models. The sound level slightly increase as the increase of Reynolds number in all models particularly when the constriction had reached 50%. Small models (7 mm diameter) generates higher sound pressure level when the constriction was less than 50%, but when the constriction reached 75 large models (10 mm diameter) generate higher sound level. These results indicate that flow impingement play important role in both condition, constricted and not constricted airways. In addition, combination of diameter and constriction percentage would determine the dominant sound source of the models which could be an indicator of the lung condition.