A cochlear implant, CI for short, can help children and adults who suffer from extreme deafness or deafness. In contrast to a conventional hearing aid, the CI directly stimulates the auditory nerve fibers. The cochlear implant consists of two parts: an external one consisting of microphone, speech processor, coil, battery or rechargeable battery.
And an internal part, the actual implant, which is composed of coil, signal processor with associated stimulator and electrodes. The implant is surgically inserted behind the ear. The patient wears the external part like a hearing aid behind the ear. There were some attempts to implant both parts, but they failed.
The external microphone receives sound vibrations and converts them into electrical signals that are routed to the implanted coil. The inner coil now passes these signals to a stimulation circuit which generates the currents for the electrodes in the cochlea. These currents are responsible for the stimulation of the auditory nerve.
Therefore, it is so important that it is still intact, otherwise the implant does not work. The stimulation creates so-called action potentials, that is electrical excitations, and transmitted to the brain, where they are identified as acoustic signals such as sounds, sounds and speech.
If speech is no longer possible through hearing and nothing is achieved with conventional hearing aids, the cochlear implant offers one more chance. This is especially the case with destroying hair cells.
An important prerequisite for the functioning of a CI, however, is that the patients are deaf only during or after the acquisition of the language, since otherwise a sound language understanding does not come about. However, this also makes it possible to treat children who already have a hearing loss at an early age but can already speak or are just learning it. Whether a CI comes into consideration for children is decided on the basis of the threshold of hearing.
This is the sound pressure level at which the human ear just hears sounds and noises. As a guideline for children 90 decibels are used for the hearing level. In the run-up to an implantation, some preliminary examinations are carried out, in which the cause of deafness is researched. Computed tomography and magnetic resonance imaging provide information about the auditory nerve and the auditory pathway. In order to be able to assess the understanding of speech correctly, adults use different tests, such as the Freiburg monosyllable test.
It checks how many monosyllables the patients understand. At a rate of less than 40 percent, a cochlear implant is advised. 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 completely new. The operation is under general anesthesia. Behind the ear there is a cut of about eight centimeters in the skin.
For the implant, the surgeon mills the skull bones. A hole is drilled in the cochlea through which the electrodes are inserted. Even during the operation, which lasts around two hours, the function of the implant is repeatedly tested. After about five days, the patient is discharged from the hospital. The healing process takes about four weeks. This is followed by outpatient adjustment appointments. For five consecutive days, the speech processor is readjusted over and over again.
This is followed by a long phase of rehabilitation, which extends over two years in adults and over three years for children. The duration varies from patient to patient. Adults who are just deaf and get their implant quickly usually only need one year. Nevertheless, listening must be completely re-learned during this time.
Noises and voices are completely different through the implant, so the hearing system needs a corresponding period of habituation. Various adaptation sections, as well as hearing and speech therapies complement the rehabilitation period. The subsequent annual check-ups are important to examine the technical function of the implant and perform hearing tests.
An operation always carries dangers. When inserting the cochlear implant, however, there are a few special risks that need to be taken into account, which the surgeon has to explain to patients intensively. Facial and taste buds may be injured during surgery as the channel for the electrodes is milled immediately in the vicinity.
It can also lead to a confusion when inserting the electrodes, which are performed instead of the cochlea in one of the three semicircular canals. Intensive monitoring during the procedure makes this mistake almost impossible. There is also a risk of meningitis infection if germs enter the cochlea via the point of entry of the electrodes.
And the patient may develop incompatibility of 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. With private funds must be negotiated separately. Follow-up costs for batteries are mostly non-refundable.