Downstream flow field structure in voice prosthesis and its effect on sound generation around the esophageal wall

This study investigates the effects of downstream flow in the voice prosthesis (Provox® Vega) on the esophageal wall during shunt vocalization to identify the dominant factors influencing the sound generated in the esophagus (the original sound in shunt vocalization). The trachea and esophagus were simulated to measure flow in the esophageal section through the voice prosthesis by using particle image velocimetry, and pressure distribution in the esophageal section was calculated by solving Poisson's equation. Downstream flow in the voice prosthesis fluctuated over time due to oscillations of the valve. This flow impinged on the esophageal wall and created a strong shear region that fluctuated over time to give rise to fluctuations in pressure at the same frequency as that of oscillations of the valve on the esophageal wall near the point of impingement. The sound pressure, estimated by using the measured velocity field based on the Ffowcs Williams-Hawkings equation, was compared with the sound pressure measured by a microphone. The results showed that temporal variations in pressure downstream of the voice prosthesis and its impinging on the esophageal wall were the main sources of the sound generated from the voice prosthesis within the esophageal section. The frequency of the generated sound depended on the frequency of oscillations of the valve.