Expiratory noise due to subglottic stenosis using direct noise calculation

Subglottic stenosis (SGS) is the narrowing of the tracheal airway near the larynx. Characterization of the adventitious respiratory noise due to SGS could aid in its diagnosis. In this study, the SGS noise during expiration is simulated through direct noise calculation. The simulations are performed using a simplified axisymmetric airway geometry that includes the trachea, the vocal folds, the supraglottal tract, and open environmental space. The effects of stenosis severity and its distance from the glottis are investigated under various flowrates that cover the typical physiological range. Two glottal configurations, normal expiration and /h/ sound production, are considered to investigate the possibility of whistling due to Helmholtz resonance. The simulation setup is validated against experimental data in the literature using a Helmholtz resonator configuration to show the capability to capture the lock-on state between acoustic feedback and flow instability. The analysis is based on the statistically steady spectrum of the acoustic signal measured near the mouth. It is found that the overall noise level increases with flow rate and whistling only happens under restricted configurations.