Influence of the flow field structure formed downstream of the human vocal cord model on the sound generated

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-Hawking (FW-H) 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 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.

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

Kosako

Hiramatsu

Fujimoto

et al. 2023

Physics of Fluids

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Flow field structure formed around voice prosthesis during shunt vocalization

Kosako

Hiramatsu

Fujimoto

et al. 2021

Transactions of the JSME (In Japanese)

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The shunt speech is a voice restoration method after total laryngectomy. However, the shunt speech has the disadvantage of poor voice quality. In shunt speech, the airflow characteristics of the voice prosthesis in the tracheoesophageal wall are greatly related to voice quality. In this study, we measured the flow field upstream and downstream of the voice prosthesis using PIV. And, optical measurements were made on the valves of the voice prosthesis. In conditions close to the expiratory flow rate during a speech, the flow field downstream of the voice prosthesis had an up-and-down wavy distribution, and the flow velocity in the vicinity of the downstream of voice prosthesis fluctuated with time at a frequency similar to that of the shunt voice. No temporal fluctuation was observed in the flow velocity under conditions exceeding the expiratory flow rate. Temporal fluctuations in the downstream flow field are associated with valve oscillations of the voice prosthesis. Outside the expiratory flow conditions, the valve does not oscillate, but within the expiratory flow conditions, the fundamental frequency of the valve oscillation increases as the applied flow rate increases. It was also confirmed that sound was generated from the voice prosthesis within the exhalation flow conditions. The generated sound coincided with the frequency of valve vibration and flow velocity fluctuation at each flow rate and may act as a source of the sound.

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Influence of the flow field structure formed downstream of the human vocal cord model on the sound generated

Cited by 2 publications

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

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

Flow field structure formed around voice prosthesis during shunt vocalization

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