Airflow-generated sound in a hollow canine airway cast

We examined the distribution of airflow-generated sound within a flexible model of canine airways. Sounds were picked up by a microphone adapted to a glass conical probe which was introduced through puncture holes in the wall of the model. We acquired 341 measurements in 31 airways between 2.0 and 19.0 mm in diameter at airflow rates from 0 to 2.5 L/s in the inspiratory and expiratory directions. We found that in the expiratory direction, the sound amplitude was approximately linearly related to airway cross-sectional area, with the greatest amplitude occurring in the largest airway. In the inspiratory direction the greatest amplitude occurred in airways of 5 to 8 mm in diameter. At all levels within the model, sound amplitude was approximately linearly related to the square of the airflow. Our findings suggest that in canine airways, the predominant vesicular lung sound-producing locations are the large airways for the expiratory component and the medium-sized airways for the inspiratory component.