Agência Brasil
Brasília – Imagine a person receiving the diagnosis of a serious hearing problem or one that is severe enough to make it impossible to use normal hearing aids. It is for these patients that the Hospital of Craniofacial Anomalies of Baurú, USP (HRAC), also known as Centrinho, in the interior of the southeastern state of São Paulo, indicates the multichannel cochlear implant, computerized prosthetics also known as “bionic ear.”
The implant is made up of internal and external components that replace the organ of Corti (which converts sounds into electric impulses that are transmitted to the brain). The implanted electrodes stimulate different parts of the cochlea (Corti region), transforming sound into electric signals. These signals are sent to the brain cortex, making it possible for the patient to hear.
Since 1990 the HRAC has executed approximately 400 surgeries, from children to aged people. This is an expensive procedure costing up to US$ 30,000 (R$ 20,000 for the prosthetics and around US$ 10,000 for the surgery), although at Centrinho, 80% of the implants are covered by the Brazilian government Single Health System (SUS).
The operation requires general anaesthetic and lasts between two and three hours. But the patient only starts hearing after the recovery period, around 45 days after the operation, when the implant is activated. “Only after that moment does the patients hearing begin,” explained speech therapist Maria Cecília Bevilácqua, of the Centrinho Audiology Research Center (CPA) and professor at the Bauru School of Dentistry (Fob). According to the professor, the device is connected to a computer system that sends data and electrical currents to the implant. This data must be programmed as the hearing system is individual and the adjustments must be taken care of one by one. “From then on the patient will need to be taught by doctors to understand the meaning of the sounds,” explained Ms. Bevilácqua.
Medical following after surgery
The patient, according to the speech therapist, will have to undergo psychoacoustic and electrophysiological evaluations. In children one year or older, this is done every two months, and in adults, every four. Given time, the tests will take place twice a year for children, and once a year for adults.
In this aspect, Maria Cecília points out the importance of a multiprofessional team that assists the patient in the attribution of meanings to the sounds. Among the professionals involved are speech therapists, ear, nose, and throat doctors, social assistants, psychologists, etc. “Centrinho is a clinical result model as it has clinical following of 100% of its patients.” The hospital currently counts on an informal chain of 60 speech therapists that work with implanted patients around the country.
“But unfortunately not all deaf people can use the implant,” says Dr. Orozimbo Alves da Costa Filho, Centrinho doctor and Fob professor. “There are various degrees of hearing deficiencies and the surgery can only be done following a protocol with criteria that must be observed.” He also explains that one of the differences between the implant and normal amplifiers – used for most deaf people – is that the latter do not amplify high frequencies very well, which are included in 70% of the consonants. Apart from that, the “bionic ear” is implanted within the ear, through surgery.
How the “bionic ear” works
The internal part pf the system is placed behind the ear (auricular pavilion), under the skin. It is made up of a magnet, a stimulator-receptor and a cable with a 22-channel electrode filament that goes from the receptor-stimulator to the cochlea. There are also two return electrodes.
The external area includes a speech processor (which is having its size reduced), responsible for coding the most important sounds for hearing. There is also a microphone that is held by a small box on the outside of the auricular pavilion that captures the sounds of the environment. A small cable makes a connection to the speech processor. Other components include the transmission aerial and cables: these are fixed externally, over the receptor-stimulator by means of a magnet.
Sound enters the system through the small microphone and is sent to the processor through a thin connecting cable. The processor selects and decodes the sounds. These electronic codes are sent back through the thin cables to the transmitter. The transmitter aerial, a plastic-covered ring, with a diameter of around 33 millimetres (mm), sends the codes to the receptor-stimulator through the skin in the form of radio waves.
The receptor-stimulator includes an integrated circuit that converts the codes into special electronic signals and sends them down the electrode filament, connected to the receptor-stimulator by a thin cable. The coded electric signals are sent to specific electrodes, programmed separately to transmit sounds that vary in intensity and frequency. These electrodes stimulate specific nerve fibres that send the message to the brain. The brain receives the signals and interprets them, making the person “have a hearing sensation.”
The multichannel cochlear implant used by the Centrinho is imported from the United States, Austria, or Australia. It is biocompatible (does not cause any rejection), as well as being approved by the Food and Drug Administration (FDA) – the North American organization that regulates the use of medicine and food – for use in children.
