At the Cochlear implant it is a hearing prosthesis for the inner ear, the cochlea, which gave the implant its name. This surgically used hearing aid offers patients with profound hearing loss the chance to hear again. What was previously not possible with either analog or digital hearing aids. A prerequisite for this, however, is a still functioning auditory nerve.
What is the cochlear implant?
With a cochlear implant, in short CI, can help children and adults with extreme hearing loss or deafness. In contrast to a conventional hearing aid, the CI stimulates the auditory nerve fibers directly. The cochlear implant consists of two parts: An external one, which consists of a microphone, speech processor, coil, battery or rechargeable battery.
And an internal part, the actual implant, which consists of a coil, signal processor with the associated stimulator and electrodes. The implant is surgically inserted behind the ear. The patient wears the external part behind the ear like a hearing aid. There have been a few attempts to implant both parts but they failed.
The external microphone receives sound vibrations and converts them into electrical signals that are passed on to the implanted coil. The inner coil then passes these signals on to a stimulation circuit that generates the currents for the electrodes in the cochlea. These currents are responsible for stimulating the auditory nerve.
This is why it is so important that it is still intact, otherwise the implant will not work. The stimulation generates so-called action potentials, i.e. electrical excitations, and passes them on to the brain, where they are identified as acoustic signals such as noises, sounds and language.
Function, effect & goals
If speech understanding is no longer possible through hearing and nothing can be achieved with conventional hearing aids, the cochlear implant still offers a chance. This is especially the case when hair cells are destroyed.
An important prerequisite for the functioning of a CI is, however, that the patient is only deaf during or after the acquisition of the language, otherwise spoken language comprehension cannot be achieved. However, this also makes it possible to treat children who suffer from hearing loss at an early age but can already speak or are learning to do so. Whether a CI for children is considered is decided based on the hearing threshold.
This is the sound pressure level at which the human ear can just barely perceive tones and noises. For children, 90 decibels are used as a guide for the hearing level. In the run-up to an implantation, some preliminary examinations are carried out to find the cause of the numbness. Computed tomography and magnetic resonance tomography provide information about the auditory nerve and the auditory pathway. In order to be able to correctly assess speech comprehension, different tests are used in adults, such as the Freiburg monosyllabic test.
It is checked how many monosyllables the patients understand. If the rate is less than 40 percent, a cochlear implant is recommended. The chances of success of this method depend on several factors: the duration of the hearing loss, the linguistic competence of the patient, the condition of the auditory nerve, and ultimately the motivation of the patient, who has to learn to hear from scratch. The operation is performed under general anesthesia. A cut about eight centimeters long is made in the skin behind the ear.
The surgeon mills a recess in the skull bone for the implant. A hole is drilled in the cochlea through which the electrodes are inserted. The function of the implant is tested again and again during the operation, which takes around two hours. After about five days, the patient is discharged from the hospital. The healing process takes around four weeks. This is followed by outpatient adjustment appointments. The speech processor is readjusted again and again for five consecutive days.
This is followed by a long rehabilitation phase, which extends over two years for adults and three years for children. The duration varies from patient to patient. Adults who have just become deaf and can get their implant quickly usually only take a year. Nevertheless, hearing has to be learned from scratch during this time.
Noises and voices have a completely different effect on the implant, so that the hearing system needs a certain period of getting used to. Various adaptation phases as well as hearing and speech therapies complement the rehabilitation period. The subsequent annual check-ups are important to check the technical function of the implant and to carry out hearing tests.
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An operation is always dangerous. When inserting the cochlear implant, however, there are still a few special risks to be taken into account, about which the operating doctor must inform the patient intensively. The facial and taste buds can be injured during the procedure, as the channel for the electrodes is milled in the immediate vicinity.
It can also lead to confusion when inserting the electrodes, which are inserted into one of the three semicircular canals instead of into the cochlea. However, intensive monitoring during the procedure makes this mistake almost impossible. There is also the risk of meningitis infection if germs enter the cochlea via the entry point of the electrodes.
And the patient can develop an intolerance to the implant materials (silicone). The cost of a CI, including the entire rehabilitation phase, is around 40,000 euros. As a rule, the statutory health insurance companies cover the costs. Separate negotiations must be carried out with private health insurers. Follow-up costs for batteries are usually not reimbursed.
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