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Invention gives instant voice to throat patients

29 November 2012

The cannula (A) and the tool (B) for inserting the voice prosthesis which is usually made of silicon. This tool is inserted into the cannula so that it can be injected into the patient's fistula according to the length required, using the calibration on the cannula.

(From left) Dr Lau, Dr Chui and Mr Chng with their invention

An NUS invention is set to help patients who lost their voice box to speak almost immediately, compared to the two-week period with the conventional procedure to create a small opening at the throat.

Dr Chui Chee Kong, Assistant Professor with the NUS Department of Mechanical Engineering, and Dr David Lau, Consultant Ear, Nose & Throat Surgeon at Raffles Hospital, work together to come up with the device that allows patient to start speaking about 10 minutes after the initial procedure.

People may lose their larynx (voice box) through cancer or injury to the throat. Those who undergo surgery to remove their larynx can recover about 80 per cent of normal speech by fitting a voice prosthesis into an opening between the trachea (windpipe) and oesophagus (food pipe). To speak, the patient has to cover the breathing opening in the throat with a thumb and forces air through the prosthesis into the oesophagus and out through the mouth.

Before placing the prosthesis, the doctor needs to puncture the wall between the trachea and oesophagus and insert a guide-wire into the opening or fistula to prevent making false passages. The fistula is then widened with dilators and a temporary rubber tube is put inside. The voice prosthesis is inserted about two weeks later when the fistula is mature.

In the course of work, Dr Lau noted that patients requiring voice restoration after surgery for laryngeal cancer have to make multiple visits to the clinic. This spurred him to get together with Dr Chui to create a simple, one-step solution that would save patients time, discomfort and money.

The new device cuts down the process by merging the various steps into a single procedure, said Dr Chui. "Most significantly, although doctors still need the nasal endoscope to guide and monitor progress during the procedure, our system ensures an immediate snug fit of the prosthesis in the passageway created between the trachea and the oesophagus. Until now, this can take some trial and error to achieve good sizing of the prosthesis."

Different people require voice prostheses of varying lengths, depending on the thickness between the food pipe and windpipe. The length of the tracheo-oesophageal puncture ranges from 6mm to 26mm, and the measurement has to be precise for each patient. The prosthesis must fit well or it may be ineffective, or leak and cause discomfort.

Mr Chng Chin Boon, Research Engineer from NUS Department of Mechanical Engineering and a member of the research team, explained that they added markings onto the cannula, a metal tube used for inserting the prosthesis. From the endoscopy, they are able to calculate the distance between the oesophageal front wall and the tracheal back wall, and size the prosthesis accurately. This eliminates discomfort such as coughing and gagging when the prosthesis has to be removed and fitted again if the measurement is incorrect.

"Most prostheses need to be changed due to wear and tear, depending on each individual. And each time, the size of the prosthesis to be inserted may differ due to tissue changes in the patient. Our invention will offer patients a more fuss-free system, cutting down time and discomfort. It will also cut down the cost for the patient as the number of procedures is reduced," noted Mr Chng.

The savings by the patient can be up to 50 per cent for the procedure that costs from S$3,000.

After successful tests on animals, the system is now ready for human trial. The researchers are planning to perform a trial of about 10 patients in a year at the Singapore General Hospital.