Electric acoustic stimulation

With the concept of the combined electric- acoustic stimulation, briefly called EAS, the hearing aid and cochlear implant technology (abbreviated CI) applied simultaneously to the same ear. The hearing aid amplifies low frequencies acoustic, while the cochlear implant electrically stimulates the middle and high frequency ranges. This allows the inner ear process the acoustic and electric stimuli simultaneously.

Results of international studies have confirmed the high synergy effect of hearing aid and cochlear implant technology, with particularly good results in speech understanding in noise and in musical perception.

Concept

Electrical stimulation of the auditory system with the help of a cochlear implant is a widely used technique for people with a moderate to severe sensorineural hearing loss, but also for adults and children with low residual hearing.

Usually, patients who suffer from a mild to moderate hearing loss benefit from conventional hearing aids. On the one hand, the acoustic gain has been proven in the lower frequency ranges. A severe hearing loss (> 70 dB) for frequencies above 1 kHz, however, may be higher than the possible gain range of the hearing aid. On the other hand, with the help of a cochlear implant ( CI) frequencies are stimulated up to 8 kHz.

The concept of combined electric- acoustic stimulation ( EAS) was first described in 1999 by C. von Illberg and J. Kiefer, University Hospital Frankfurt. That same year, the first EAS patient was implanted.

Indications

There are patients who have a profound hearing loss for low frequencies some residual hearing and for high frequencies. These persons can not benefit from the classical gain a hearing aid because of the severe hearing loss in the high frequencies, since they, despite the best adaptation of the hearing do not have sufficient understanding of language. Due to their good residual hearing in the low frequencies, they are also not classical candidate for a cochlear implant. The indication for EAS is based on three factors:

Audiogram

  • <1.5 kHz or less no hearing loss
  • > 1.5 kHz high-grade, bordering to profound, sensorineural hearing loss / hearing impairment sensorineural

Language comprehension

The Freiburg monosyllable should have a result equal to or worse than 65 % speech intelligibility at 65 dB with the best possible hearing aid.

Medical history

Contraindications:

  • Progressive hearing loss
  • Autoimmune disease
  • Hearing loss due to meningitis, otosclerosis or ossification
  • Miss or malformation of the cochlea
  • Contraindications of the outer ear towards hearing aids

The handset retaining implantation

A special surgical technique is the key to maintaining the balance and hearing, as in a normal cochlear implant surgery, the residual hearing is destroyed with a high probability. Important factors for the preservation of residual hearing are:

  • Use of special electrodes atraumatic
  • Smallest possible acoustic trauma during drilling of the cochleostomy
  • Smallest possible mechanical trauma due to the opening of the cochlea and the insertion of the electrodes
  • Prevention of inflammatory responses ( contamination with blood, bacteria from the middle ear, bone dust, etc. )
  • Use of special drugs to the listener stop

There are two common methods to introduce the electrode into the cochlea:

  • Through the round window
  • Through a cochleostomy

Lately enjoys the Warsaw technique gaining in popularity because it is considered less traumatic. The best results were achieved with an electrode insertion depth of 18 mm, since this length coincides with the location for the physiological recording of cochlear frequency at 1000 Hz. Therefore, all frequencies below 1000 Hz and acoustic frequencies above are electrically stimulated.

To ensure a successful treatment of EAS patients, companies offering EAS as a treatment method, surgeons and specialists offer the opportunity to participate in training courses for this special surgical technique.

EAS electrode

Longitudinal studies show that a low effort as possible during insertion of the electrode increases the chances to get the easily destructible structures within the cochlea. Thus, the mechanical flexibility of the electrode is a key factor for the preservation of residual hearing.

EAS audio processor

There are currently two CI manufacturers, namely MED -EL Cochlear and. The hearing aid is integrated in the ear hook (BTE = behind-the- ear processor, or BTE = Behind-the -ear ), and the amplified signals are routed to the Maßohrpassstück in the ear canal. The ear piece, which is used for the acoustic part is identical to that of a conventional hearing aid and can be easily replaced. The sound recording is the same as the CI through the microphone of the BTE processor. The signal is separated and then parallel to the acoustic listening optimized accordingly ( in the low frequencies ) and for the cochlear implant stimulation ( in the high frequencies ). This allows the user a clear and precise localization of sounds.

Admission

In Europe, the EAS systems are already approved, is currently performed in the United States, a clinical examination of both systems.

Long-term experiment
302666
de