Cochlear implant

from Wikipedia, the free encyclopedia
This article or the following section is not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.
Cochlear implant

The cochlear implant (English cochlear implant , CI) is a hearing prosthesis for the deaf and deaf people whose auditory nerve as part of body of the auditory perception is still functional.

The CI system consists of a microphone , a digital signal processor , a transmitter coil with magnet and the actual implant , which is made up of another magnet, a receiver coil, the stimulator and the electrode carrier with the stimulation electrodes. The electrodes are inserted into the cochlea (cochlea). The receiving coil is placed under the skin in the cranial bone near the auricle. The transmitter coil of the processor is attached to the scalp with the help of the magnets above the receiver coil of the implant. The voltage is supplied to the implant through the scalp by means of electromagnetic induction . The signal is transmitted with high frequency waves . Sometimes only the implant is called the CI and the entire system is called the CI system .

From the 1960s, William F. House in the USA , Graeme Clark in Australia and the married couple Ingeborg and Erwin Hochmair in Austria did pioneering work in developing this device concept . House dealt with a single-channel transmission, while Clark and the Hochmair couple were ultimately more successful in application and marketing with a multi-channel transmission concept.

operation area

A CI fitting is indicated when the best conventional sound-amplifying hearing aids can no longer be used to achieve adequate speech understanding. This is the case from a critical number of destroyed hair cells . In Germany , for example, the Freiburg monosyllabic test is used to examine speech understanding with hearing aids in adolescents and adults. By comparing the speech understanding of average CI and hearing aid wearers, it can be determined that a speech understanding of monosyllables with the best hearing aids of only 30% or less at normal speech volume (65 dB SPL ) can be significantly improved with CIs. Over 75% of CI wearers understand more than 30% monosyllables, 50% even more than 62% monosyllables. In general, the recommendation applies that patients who understand less than 40% monosyllables in normal loud speech should seek advice from an implanting clinic as early as possible about the current possibilities of modern CIs. The chances of success largely depend on the duration of the critical hearing loss, language skills, the condition of the auditory nerves, the presence of central auditory perception and processing disorders and the patient's motivation to recognize and identify the often variable hearing impressions and speech sounds.

For adults who are deaf before or during language acquisition, CI treatment is futile, as the auditory nerve has already deteriorated too much due to the long duration of the lack of irritation.

In young children, it is not possible to evaluate language comprehension on the basis of the monosyllable test. Here, a decision is usually made based on the hearing threshold . On the basis of the evaluation of modern CIs, a hearing threshold of 90 dB HL or worse from 1000 Hz and higher as an indication for CI treatment is considered to be a benchmark .

functionality

The cochlear implant consists of an external part (consisting of microphone, speech processor, battery or rechargeable battery and coil) and an implanted part (consisting of coil, signal processor with stimulator and electrodes for stimulation). The external part is usually worn behind the ear (attempts to implant this unit have also failed so far) and transmits digital information to the implanted coil via the external coil. The coils are each equipped with a magnet to ensure correct positioning. The inner coil conducts the received signals to a stimulation circuit, which generates the necessary currents for the electrodes in the cochlea. The currents excite the auditory nerve of the ear, which is downstream of the hair cells . Different excitation sites stimulate nerves with different frequency adaptations. The strength of the electric current is decisive for the loudness.

Manufacturers use different coding and stimulation strategies to digitize the audio signal from the microphone and stimulate it within the cochlea. The electrodes can stimulate the auditory nerve in parallel or sequentially. With parallel stimulation, two or more electrodes can stimulate the auditory nerves at the same time, with sequential stimulation the stimulation takes place one after the other. Despite different stimulation strategies and speech codings, it can be seen that speech understanding is about equally good with the three big manufacturers.

implantation

The implantation is usually carried out under anesthesia , with the first operations only being carried out with local anesthesia . Before the operation, the hair behind the ear was often shaved away, but with today's methods this is hardly necessary. Then the skin behind the ear is cut open 5 to 8 cm long and folded back. A recess is milled out of the now exposed skull bone, which will later receive the stimulator housing of the implant. In children, the meninges (dura) are partially exposed. A canal is then cut through the temporal bone that extends into the middle ear. It must be placed in such a way that the round window that leads to the inner ear is accessible. A small drill is then inserted through this channel and a hole is drilled into the cochlea. This usually happens near the round window. The electrode bundle of the implant is inserted through the hole as deeply as possible into the Scala tympani . The thin connection cable is attached to the petrous bone to prevent the electrode set from slipping out.

The actual implant of a CI system (model Cochlear Freedom 24 RE)

Depending on the surgical technique, the canal in the petrous bone is now filled with bone material or left open. The implant can then be lashed with medical thread in the recess provided for it. Finally, any potential equalization electrode is pushed under the scalp and finally the skin flap is folded back and sewn up. The function of the implant is tested with special equipment during the operation. Years ago the success of the operation could only be assessed very imprecisely by triggering the stapedius reflex , today the response of the auditory nerve to electrical excitation is measured and evaluated qualitatively and quantitatively with special telemetry devices (neuro-response telemetry; neuro-response telemetry). Response imaging). The intraoperative determination of the electrically triggered nerve action potentials of the brain stem ( BERA, ABR ) provides more detailed information about the state of the auditory pathway in the brain stem leading to the brain . This means that the level of maturation of the hearing pathway can be determined even in small children.

Hearing sensation and hearing training

External unit cochlear system

The electrical stimuli in the cochlea create individual hearing sensations in the CI wearer that are different from those of people with normal hearing. The neural mechanism for processing acoustic stimuli is so flexible that it is adapted to these sensations. An intensive, long hearing training after the operation is necessary in order to assign the new signals to the known hearing patterns. Therapy with CI is similar to learning a foreign language. The period of time that is required for language comprehension varies from person to person. For children, the duration is estimated at around two to three years. Adults who are currently deaf and who receive early cochlear implants usually require a shorter period of rehabilitation.

Medical risks

In addition to the general risks of an operation, there are special risks.

  • There is a certain risk to the facial nerve and the taste nerve because the channel for the electrode carrier is milled in their vicinity. The surgeon must therefore proceed extremely carefully with the help of facial monitoring so as not to injure the facial and taste buds.
  • There is a small risk of meningitis after implantation. This is the case when germs penetrate via the entry point of the electrode bundle.

scope

On December 31, 2011 there were around 300,000 CI users worldwide, around 30,000 of them in Germany.

Care of small children

CI care for severely hard-of-hearing or deaf children is now the medical standard due to the superior hearing and language acquisition performance compared to hearing aids and is accepted by a large majority of the parents concerned. Restoration is recommended before the age of 2, as the results deteriorate as the age of implantation increases. An implantation after the age of eight appears to be less sensible for most children who are deaf from birth, as acquisition or improvement of spoken language through hearing is then only possible to a very limited extent. Of course, this does not apply if a child could be adequately provided with hearing aids earlier and speech can no longer be sufficiently understood with hearing aids until later due to a deterioration in the hearing threshold. The costs for both unilateral and bilateral implantation are fully covered by health insurance companies in Germany and by disability insurance in Switzerland .

Supply on both sides

For many years only one ear was usually implanted, even if both ears were deaf. Long-term psychoacoustic research results on binaural hearing (and of course the everyday listening experience when one closes an ear) were able to prove that speech understanding with just one ear is worse than with two ears, especially in (the usual, everyday) noisy listening situations . In children, phases of one-sided hearing should therefore be avoided. When it comes to hearing aids, this fact has been taken into account in standard two-eared care since the 1970s.

Since around 2000, especially since the introduction of digital signal processors worn behind the ear, almost all CI clinics have also offered two-ear CI care. The care of patients who are deaf on one side (possibly with hearing aids for the other ear) is possible and is carried out at many clinics.

Rejection by representatives of a deaf culture

The implantation is rejected by some of the people who feel they belong to or feel connected to the deaf culture . Harlan L. Lane even described the proponents of CI as audistic . He did not view the deaf as disabled, but as members of an ethnic group.

Similar techniques

literature

Guidelines

Review articles

Others

  • Elisabeth Calcagnini Stillhard: The Cochlear Implant. A challenge for the hearing impaired education . Edition SZH / SPC, Lucerne 1994, ISBN 3-908263-03-4 .
  • Julia Koch: Discoverer in the world of sounds . In: Der Spiegel . No. 13 , 2005, pp. 156 ( online - with current figures).
  • Sabine Müller, Ariana Zaracko: Do Deaf Infants Have a Right to a Cochlear Implant? In: Neurology. 4, 2010, pp. 244-248. (PDF)
  • Marion Hermann-Röttgen (Ed.): Cochlea-Implantat. A guide for those affected and therapists. Trias, 2009, ISBN 978-3-8304-3530-3 .

Web links

Individual evidence

  1. ↑ Hannover Medical School: The future of cochlear implantation: MHH implants for the first time under local anesthesia. Retrieved November 10, 2018 .
  2. ↑ Deutsche Cochlear Implant Gesellschaft eV ( Memento of the original from April 11, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / schnecke-online.de
  3. ↑ A. Kral, GM O'Donoghue: Profound deafness in childhood. In: New England J Med. 363, 2010, pp. 1438-1450.
  4. ↑ Niparko include: Spoken language development in children Following cochlear implantation. In: JAMA. 303, 2010, pp. 1498-1506.
  5. ↑ Harlan L. Lane: The Mask of Benevolence: Disabling the Deaf Community. New edition 2000. Dawn Sign Press. (German: The Mask of Mercy. Suppression of the language and culture of the deaf community. Signum, Hamburg 1994)