Improving the life of tracheo-oesophageal fistula speech valves

Home » Case Studies » Speech Valves

This is a joint project between Medical Engineering, Biological Sciences and Otolaryngology (Hull and East Yorkshire Hospitals NHS Trust). The work is funded by Action Medical Research.

The restoration of vocal function after laryngectomy is one of the challenges in head and neck cancer surgery. Currently, the most common approach is to use a prosthetic valve, which allows air from the trachea to be diverted into the oesophagus. However although the initial performance of these valves is excellent, they deteriorate rapidly due to biofilm growth and fail within a very short time - frequently less than 3 months. The aim of this research is to improve significantly the life of these tracheo-oesophageal fistula speech valves.

Clinical background
    The most common types of tracheo-oesophageal fistula (TOF) speech valves are based on the design first proposed by Blom in 1979 and are manufactured from medical-grade silicone. Silicone is a well-tried and widely accepted biomaterial that is used in a number of other implants designed for long-term use. It is an attractive material because of its stability, biocompatability and compliance, which in this application allows for easy insertion and alignment in the soft tissue. However, when used in speech valves, the material is exposed to a particularly hostile and non-sterile environment. The result is rapid surface colonisation, biofilm growth and valve deterioration, which leads to valve replacement after an average of only 3 months.
    A valve needs replacing when it fails to function correctly, which occurs when leakage through the valve causes the aspiration of saliva or swallowed liquid into the trachea, or when phonation becomes increasingly difficult in terms of the initiation of speech and the maintenance of speech.
    Current evidence indicates that the valves do not wear out or mechanically fail, but cease to operate correctly because of the colonisation and biofilm growth, but the precise mechanisms of the development of the biofilm are multifactorial and complex

Project description
    The aim of this research is to understand how the biofilm affects the mechanical properties of the silicone, and then to examine the effect of the biofilm on the performance of the valve by finite element analysis. Once this has been fully understood, the aim is to investigate new designs of valve that are tolerant to the biofilm.