Improved speech without vocal cords

Dutch otolaryngologist Marein van der Torn hoped to develop a prosthesis that would improve the voice of people who had lost their vocal cords. He investigated the possibilities of a new type of voice prosthesis that produces vocal sound. The concept could be useful for female patients with a very weak voice: it would strengthen their voice and enable it to achieve a female pitch again. However, various practical problems need to be solved before the voice prosthesis can be used.

Sometimes the larynx, containing the vocal cords, needs to be surgically removed in throat cancer patients. Since the 1980s most of these patients have learnt to speak again with the help of a small silicone rubber valve placed between their windpipe and oesophagus.

This valve enables them to use the uppermost sphincter of their oesophagus as a sort of vocal chord. However, this alternative voice sounds often gruff and is lower than the natural voice. Female patients in particular find the low pitch troublesome. Moreover, if the uppermost sphincter of the oesophagus is too weak, the voice is not strong enough to be understood clearly.

Together with the University of Groningen, Van der Torn and his colleagues at the Vrije Universiteit in Amsterdam developed a new type of valve that produces its own vocal sound. That sound is produced by a small silicone rubber flap in the valve, which acts as an artificial vocal chord.

A different flap was developed for male voices than for female voices. The vibrational behaviour of these flaps, the air resistance and the sound produced were extensively investigated in vitro. These new voice prostheses were also trialled in a group of patients at the VU University Medical Center and compared against the voices of these patients without the silicone rubber flap.

From these trials it emerged that for the time being only female patients with a very weak voice would benefit from the new voice prosthesis: their voice becomes more powerful and once again achieves a female pitch. The new voice prosthesis cannot be used yet because the silicone rubber flap is easily impaired by tough mucus coughed up by the majority of patients.

Marein van der Torn’s research was funded by Technology Foundation STW.