Direct Acoustic Cochlear Stimulator (DACS)

DACS overview

There is not yet a dedicated therapy for severe to profound mixed hearing loss. Patients are normally treated either with a conventional hearing aid or the combination of a conventional hearing aid and stapedectomy.

Direct acoustic cochlear stimulator is based on the principle of bypassing the natural sound transmission structures of the ear in order to directly provide an amplified signal to the cochlea. In this way the conductive losses have no longer to be compensated by increased output power and the required amplification is determined by the sensorineural hearing loss only.

Semi-implantable investigational device consists of following components:

  • An externally worn audio processor
  • A percutaneous connector
  • An implantable microactuator.

Working Principle

Direct Acoustic Cochlear Stimulator Working
Fig 1: Direct Acoustic Cochlear Stimulator
The actuator is placed in the mastoid bone, just behind the external auditory canal. It generates vibrations, bypassing the external and the middle ear, that are directly synced to the inner ear fluids. The system is able to provide an equivalent sound pressure level of 125 dB over the frequency range between 125 and 8000 Hz.

  1. The sound processor captures sounds and converts them into digital code.
  2. This code is then transmitted through the coil to the implant.
  3. The implant then converts the sound to an analog signal and sends it to the actuator.
  4. The actuator converts the analog signal to mechanic vibrations of the artificial incus.
  5. Artificail incus stimulates the cochlea via the stapes prosthesis

Who will benefit from middle ear implant?

To help chose the right candidate there are stringent protocols in place in order to reduce the risks of implantation. These aspects cover issues around the surgery and the device. anyone with following can be considered as coandidate doe DACS:

  • have profound sensorineural hearing loss in both ears with a functioning hearing (auditory) nerve
  • good speech, language, and communication skills
  • showing not much benefit from the latest model of high powered hearing aids
  • having no pre-existing medical reason which will create complication for surgery
  • realistic expectations about results
  • support of family and friends

Surgical Procedure

Specially developed retromeatal microsurgical approach is used to implant the device. After removing the stapes, a conventional stapes prosthesis is attached to the transducer and positioned in the oval window to allow direct acoustical coupling to the perilymph of the inner ear. As in a conventional stapedectomy, to revive the natural sound transmission of the ossicular chain, another stapes prosthesis is attached in coordination to the first one into the oval window and connected to the patient's own incus.

The direct access to the inner ear via the stapes prosthesis eliminates the conductive part of the hearing loss and closes therefore the air-bone-gap. The amplified deflections compensate for the sensorineural hearing loss. Both elements together result in aided thresholds those are close to the upper edge of the speech banana. This allows to follow again a conversation at normal sound levels.