An in Vitro Study of Voice Prosthesis Design

This dissertation, "An in Vitro Study of Voice Prosthesis Design" by Ho-chun, Horace, Lam, 林浩俊, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled "An In Vitro Study of Voice Prosthesis Design" Submitted by Horace Ho-chun Lam for the degree of Master of Philosophy at the University of Hong Kong in June 2005 Improvements in quality and convenience have boosted the popularity of prosthetic voice rehabilitation in the last decade. This voice rehabilitation method involves implantation of a voice prosthesis in the neck between the trachea and esophagus. The prosthesis is basically a valve device designed to shunt pulmonary air to the mouth to produce a voice, and should ideally retain the function of the epiglottis. Nevertheless, after prolonged usage, the prosthesis will be colonized by Candida in a nutritious environment, causing leakage and consequent malfunction. In the last decade, researchers have developed prototypes with valves made of Candida-resistant material or adopted a different opening mechanism. While these modifications appear to have treated the leakage problem successfully, they have also produced aerodynamic problems. It is therefore necessary either to develop a completely new type of prosthesis or to make appropriate modifications to the present prototypes. This study explores some possible design improvements. We consider first the prosthesis core, and use a convergent core to replace the original cylindrical one. From our theoretical and experimental data, it is found that the valve opening angle, trans-prosthesis pressure difference, airflow resistance and bending constant will increase, but to a different extent, as the core convergence increases. Moreover, with no emphasis on the relative importance of the four i properties, the optimum core outlet radius at the normal phonation airflow rate is found to be 1.15 mm. We next study the prosthesis valve, and consider a design modification where the valve tracheal surface is made convex and the esophageal surface flat. From our computational data, it is found that a valve tracheal surface of higher convexity gives better results in terms of distribution and intensity of both pressure and shear stress. Limiting the valve thickness at 1.20 mm as in the original prosthesis, the maximum convexity is found to be 3.72 mm in radius and 1.00 mm embedded into the core. The two principles of modification considered in this study, namely convergent core and convex tracheal surface, are proved to be aerodynamically favorable. Further in vivo experiments are recommended to obtain an optimum dimensions to satisfy patients' preferences and take into account other researchers' prototypes. ii DOI: 10.5353/th_b3151496 Subjects: Artificial larynx