Electro-acoustic stimulation
With the concept of combined electrical-acoustic stimulation , called EAS for short , the hearing aid and cochlear implant technology (CI for short) are used simultaneously in the same ear.
The hearing aid amplifies the low frequencies acoustically, while the cochlear implant stimulates the medium and high frequency ranges electrically (so-called hybrid system). This enables the inner ear to process the acoustic and electrical stimuli simultaneously.
The results of international studies confirm the high synergy effect of hearing aid and cochlear implant technology, with particularly good results in speech intelligibility in noise and in musical perception.
concept
The electrical stimulation of the auditory system with the help of a cochlear implant is a widely used technique for people with moderate to severe sensorineural hearing loss, but also for adults and children with poor residual hearing.
Typically, patients with mild to moderate hearing loss can benefit from conventional hearing aids. On the one hand, the acoustic amplification in the lower frequency ranges has proven itself. However, severe hearing loss (> 80 dB) for frequencies above 1 kHz may be above the possible gain range of the hearing aid . On the other hand, frequencies of up to 8 kHz can be transmitted with the help of a cochlear implant (CI).
As early as the mid-1990s, individual patients were known whose low-frequency residual hearing was retained after the implantation. The concept of the intended combined electrical-acoustic stimulation (EAS) was first described in 1999 by C. von Illberg and J. Kiefer from the Frankfurt University Hospital . The first EAS patient was implanted that same year.
Indications
There are patients who have some residual hearing for low frequencies and profound hearing loss for high frequencies. Because of the severe hearing loss in the high frequencies, these people cannot benefit from the classic amplification of a hearing aid, as they do not have sufficient speech understanding despite the best fitting of the hearing aid. However, because of their good residual hearing in the lower frequencies, they are not classic candidates for a cochlear implant. The indication for EAS is based on three factors:
- Audiogram
- Speech intelligibility
- Medical history
Audiogram
- <1.5 kHz no or little hearing loss
- > 1.5 kHz high-grade sensoneural hearing loss / sensoneural hearing impairment bordering on deafness
Speech intelligibility
The Freiburg monosyllabic test should have a result equal to or worse than 50% speech understanding at 65 dB SPL with the best possible hearing aid.
Medical history
Contraindications:
- Progressive hearing loss
- Autoimmune disease
- Hearing loss due to meningitis, otosclerosis, or ossification
- Malformation or malformation of the cochlea
- Difference between air and bone conduction> 15 dB
- Contraindications of the outer ear to hearing aids
The hearing-preserving implantation
A special surgical technique is the key to maintaining residual hearing, as there is a high probability that residual hearing will be destroyed during normal cochlear implant surgery. There is no guarantee that the residual hearing will actually be preserved. It happens again and again that some initial residual hearing is lost even months after the operation. Important factors for maintaining residual hearing are:
- Use of special atraumatic electrodes
- Smallest possible acoustic trauma when drilling the cochleostomy
- Minimal mechanical trauma due to the opening of the cochlea and the insertion of the electrodes
- Preventing inflammatory reactions (contamination with blood, bacteria from the middle ear, bone dust, etc.)
- Use of special drugs to maintain hearing
There are two common ways to insert the electrodes into the cochlea:
- Through the round window
- Through a cochleostomy
Lately, the introduction through the round window has become increasingly popular as it is viewed as less traumatic. The best results were achieved with an electrode insertion depth of 18 mm, as this length also corresponds to the physiological position for the frequency recording of the cochlea at 1000 Hz. Therefore, all frequencies below 1000 Hz are acoustically stimulated and the frequencies above are electrically stimulated.
In order to ensure successful treatment of EAS patients, companies that offer EAS as a treatment method offer surgeons and specialists the opportunity to take part in training courses for this special surgical technique.
EAS electrodes
Long-term studies show that the slowest possible introduction of the electrode with little force increases the chances of preserving the easily destructible structures within the cochlea. The mechanical flexibility of the electrode is therefore one of the key factors in maintaining residual hearing.
EAS (Hybrid) audio processor
There are now several CI manufacturers, namely Advanced Bionics , MED-EL and Cochlear . The hearing aid is integrated in the ear hook (BTE = behind-the-ear processor or BTE = behind-the-ear), and the amplified signals are passed on into the ear canal via the custom-made earpiece. Advanced Bionics already offers modern "Ex receiver technology". The earpiece that is used for the acoustic part is identical to that of a conventional hearing aid and can therefore be easily replaced. As with CI, the sound is recorded via the microphone of the BTE processor. The signal is separated and then optimized in parallel for acoustic hearing (in the low frequencies) and for cochlear implant stimulation (in the high frequencies). This allows the user a clear and precise localization of sounds.
Admission
The EAS systems have already been approved in Europe, and both systems are currently undergoing clinical testing in the USA.
See also
Web links
literature
- C. v. Ilberg, J. Kiefer, J. Tillein, T. Pfennigdorff, R. Hartmann, E. Stürzebecher, R. Klinke: Electric-acoustic stimulation of the auditory system. In: ORL. 61, 1999, pp. 334-340.
- H. Skarzynski, A. Lorens, A. Piotrowska, I. Anderson: Partial deafness cochlear implantation provides benefit to a new population of individuals with hearing loss. In: Acta Otolaryngol. Vol. 126/9, 2006, pp. 934-940.
- W. Gstoettner, S. Helbig, N. Maier, J. Kiefer, A. Radeloff, O. Adunka: Ipsilateral Electric Acoustic Stimulation of the Auditory System: Results of Long-Term Hearing Preservation. In: Audiology & Neurotology : 11 (suppl 1), 2006, pp. 49-56.
- U. Baumann, S. Helbig: Hearing with combined electrical and acoustic stimulation. In: HNO : 57/6, 2009, pp. 542-550.
Individual evidence
- ↑ advancedbionics.com ( Memento from January 7, 2018 in the Internet Archive )
- ↑ cochlear.com ( Memento from June 21, 2013 in the Internet Archive )
- ↑ Selection criteria for EAS candidates
- ↑ medel.com