Cochlear implant
The cochlear implant (English cochlear implant, CI ) is a hearing prosthesis for the deaf whose auditory nerve is still functioning.
CI - system consists of a microphone, a digital voice processor, a transmitter coil with the magnet and the actual implant, which consists of a further magnet, a receiving coil, the stimulator and the electrode carrier with the stimulation electrodes. The electrodes are inserted into the ear (cochlea ). The receiving coil is placed behind the ear, under the skin. The coil of the processor by means of the magnet adheres to the head skin, to the receiving coil of the implant. The power supply of the implant is carried out through the scalp by means of electromagnetic induction. The signal is transmitted with high frequency waves. Sometimes only the electrode bundle as CI, the entire system is called the CI system.
Essential role in the development were the American surgeon William F. House, the Australian Graeme Clark and the Austrian couple Ingeborg and Erwin Hochmair.
Area of application
A cochlear implant is indicated when using the best of conventional sound- amplifying hearing aids not have sufficient language comprehension more can be achieved. This is the case with the destroyed hair cells. The earlier statement that a CI for deaf people completely out of the question is obsolete. In Germany, for example, used the Freiburg monosyllable test for the investigation of language understanding with hearing aids in adolescents and adults. Here you can find by comparing the language comprehension average CI and hearing aid users that a language understanding of monosyllabic words with best hearing aids by only 30% or less at normal speech volume (65 dB SPL) can be significantly improved with CIs. About 75 % of the CI users understand more than 30% monosyllables, 50 % even more than 62 % monosyllables. In general, the recommendation that patients with less than 40 % Einsilberverstehen should seek advice as early as possible at a clinic implanted on the current capabilities of modern CIs at normal loud speech applies. The chance of success depends largely on the duration of deafness, language skills, the condition of the auditory nerve, the presence of central auditory perception and processing disorders and the motivation of the patient to learn the unfamiliar auditory sensations and speech sounds.
In deaf adults who are deaf already at or before the acquisition of language, a cochlear implant is not advised, since a loud verbal comprehension is usually not expected.
In small children, an evaluation of speech understanding based on the Einsilbertests is not possible. Here one usually decides on the basis of the hearing threshold. On the Valuation basis of modern CIs considered as a standard gauge hearing threshold of 90 dB HL or worse from 1000 Hz and higher than indication for cochlear implantation.
Operation
The cochlear implant consists of an external portion (consisting of a microphone, speech processor, battery and coil) and an implanted part. The external part is usually worn behind the ear ( attempts to implant this unit also failed up to now ) and a magnet implanted coil is energized. This coil excited via electrodes to the auditory nerve of the ear, which are connected downstream of the hair cells. Thus, only the cochlear implant is used when the hair cells are damaged, because a conventional sound amplifying hearing aid is dependent on this. For transmission the manufacturers use different coding strategies. The electrodes can stimulate the auditory nerve in parallel or sequentially. In the parallel two or more stimulating electrodes may stimulate the acoustic nerve at the same time, in the sequential stimulation of the stimulation is carried out in succession. Despite different strategies in the coding shows that speech understanding in the three major manufacturers is good about the same.
Implantation
The implantation always occurs under general anesthesia. Before the surgery sooner, the hair was often shaved off behind the ear, in the present methods is, however, hardly necessary. Then the skin is cut behind the ear 5-8 cm long and folded back. A recess is milled out of the now exposed skull bone, which should later take up the stimulator implant. In children, in this case the meninges ( dura ) is partially exposed. Then, a channel is cut through the temporal bone, which extends to the middle ear ( tympanotomy ). It must be placed so that the round window, which leads to the inner ear, is accessible. Through this channel through a small drill is now introduced and drilled a hole in the cochlea. This usually happens near the round window. Through the hole the electrode bundle of the implant is maximum insertion depth into the scala tympani. The thin connection cable is fixed to the temporal bone to prevent slipping of the electrode sets.
Depending on the surgical technique of the channel in the petrous bone is then filled with bone or left open. The implant can then be lashed with medical yarn in the appropriate recess. Any existing equipotential electrode will be placed under the scalp, and finally folded back and sewn up the flap of skin at the end. Even during the operation, the function of the implant is tested with special equipment. Had you can estimate very imprecise years ago the success of the surgery only by triggering the acoustic reflex, is still additionally measured during the operation, the response of the auditory nerve to electrical stimulation with special telemetry devices qualitatively and quantitatively and evaluated (neuro -response telemetry; Neuro- Response Imaging). Further information on the state of the brain leading to the auditory pathway in the brain stem provides the intraoperative determination of the electrically induced nerve action potentials of the brain stem ( EBERA, EABR ). Hereby the auditory pathway can also be determined in young children the maturation status.
Auditory perception and auditory training
The electrical stimuli in the cochlea generate individual auditory sensations, some of which are different than those of normal hearing in the CI recipients. Neurological mechanism for the processing of acoustic stimuli, but is flexible enough to adjust to the sensation occurs. An intensive, long listening sessions after surgery is required to allocate the new signals known Hörmustern. The therapy with the CI is similar to learning a foreign language. The period required for speech understanding is individually different. For children, the duration is estimated to be about two to three years. Adults who are deaf and just be early supplied with a cochlear implant, usually require a shorter rehabilitation period.
Medical risks
The general risks of surgery appear specific risks: a certain risk for the facial nerve and the nerve of taste, as the channel for the electrode carrier is milled around him. The surgeon must therefore be extremely careful to proceed with the help of Facialismonitoring so as not to injure the facial and taste buds.
Extremely rare, the electrode set is introduced by mistake instead of the cochlea in one of the three semicircular canals of the vestibular system. During surgery, a Hörnervenmonitoring is performed with the proper functioning of the CIs and the functioning of the auditory nerve is detected. There is a small possibility of a meningitis infection after implantation. This is the case when nuclei of the entry point of the electrode bundle reach the cochlea. After the operation (eg, silicone ) develop in extremely rare cases, patients have an intolerance to the materials used, the implant. The surgical wound does not heal then and remains lit.
Scope
31 December 2011, the world has about 300,000 CI recipients, including about 30,000 in Germany.
Caring for small children
The CI treatment of the severely hearing or deaf infants is today because of the superior compared to hearing aids hearing and speech acquisition performance medical standard and is adopted by a large majority of affected parents. The supply is before the age of 2 recommended because the results are worse with increasing implantation age. Implantation after the eighth year of life appears to be less useful for most deaf children from birth because an acquisition or improvement of spoken language through hearing only then is still very limited. This of course does not apply if a child was previously adequately supplied with hearing aids and later language with hearing aids can not be sufficiently understood by a deterioration of hearing threshold. The costs are covered for both single-sided and double-sided for implantation in Germany completely by health insurance in Switzerland by the disability insurance.
Importance of the two time windows of language development for early detection and intervention
The two periods are consistent with recent research agreement in the field of experimental neurophysiology and neuroscience about the existence of a critical ( permanently fixed ) and a sensitive ( particularly receptive ) period in the development of man. They confirm the importance of early detection ( newborn ) and intervention ( hearing amplification, ear training ).
The first time window (critical period) extends up to 8-9 months. In the 1970s, the language teacher will Ciwa Griffiths discovered in the care of deaf infants with bilateral hearing aids, hearing aids that could be sold after a few months because the infants had now become a normal hearing. Your clinical trial from 1969 to 1973 to 21 deaf infants showed that 67 % of infants to eight months took part in the Age of the study and were supplied with a hearing aid, a normal hearing developed, while the after none of the infants, the only 8 months hearing aids received was the case. In a similar study, which was conducted by the Otologisten Arpad idol at the Janos Hospital, Budapest, Hungary 1978-1981 with 68 deaf infants were able to develop a normal hearing 51 ( 75%), the remaining 17 had deaf parents and their hearing aids were only after 8.5 months.
With the study of filial learning in 2000 was Alison Gopnik of the University of California after that seven -month-old Japanese and American babies could distinguish well between "R" and "L" equal to what after ten months no longer possible for the Japanese baby had. This study confirms results of brain research that the brain controlled by the ears, specializing in the native language and therefore foreign sounds that it does not stop in the language environment, limiting after 8-9 months. For deaf children who receive no sensory input, the restriction is still massive.
The second time window ( sensitive period) ranging from 8 to 9 months to about 3.5 years, which is considered as a ripening period of language development. The longer the brain is deprived of acoustic input, the greater the resulting sensory deprivation, which causes a lack of sensory stimulation of the brain. Not only that sensory deprivation prevents auditory learning, it also prevents neuronal growth. In the absence of normal stimulation, there is a sensitive period to about 3.5 years in which the human central auditory system remains maximum plastically after the age of 7 years, the plasticity is greatly reduced ..
Bilateral implantation
In recent years, usually only one ear was implanted, even and especially when both ears were deafened. On the one hand, the allegation of unoperated led " spare ear ", which in the future for improved implants or other forms of therapy ( hoping to regrow the hair cells again) would be available. On the other hand, the insurers to pay for only the unilateral implantation.
Many years of psychoacoustic research results on binaural hearing ( and of course the everyday listening experience, if you look at an ear seals ) but were able to demonstrate that especially understanding speech with only one ear is worse than with two ears and this especially in ( the usual everyday ) noisy environments. Add to this the increasing neurophysiological evidence that the auditory pathway and the auditory cortex of the unserved deaf ear after birth can not develop and is partially re- hearing ear, so that after long periods of unilateral deafness a good hearing in this ear is no longer achieved - this applies, however, the only uses for single-sided deafness early after birth. In children phases of unilateral hearing should therefore be avoided. When hearing aids had been allowed for this circumstance since the 70s in the binaural standard care.
Around since 2000, especially with the introduction of behind-the- ear digital signal processors, as well as the binaural cochlear implantation is offered with good success in many CI clinics.
Criticism
Similar to the methods of dispute implantation is rejected by one of the people who feel the Deaf culture associated or connected. This is based on the fear that in the subsequent rehabilitation, the use of sign language is subordinated to the promotion of spoken language. The deaf child should not be obstructed by the implantation of the way into the Deaf culture. Critics of this county evaluate the propagation of the CI as a targeted non-acceptance of deafness and of living with deafness, which it positive. Harlan L. Lane refers to the proponents of CI even as audi table. He considers deaf as not disabled, but as members of an ethnic group. To address the concerns of deaf CI opponents, children will be offered sign language in some implanted.
In his autobiography, the deaf-born Peter Hepp describes how he has lived as a 33 -year-old, the operation and effect of the cochlear implant. Hepp was a negative assessment of his CI. Conversely deliver Fiona Bollag et al. a success story.