Hybrid Cochlear Implants

Cochlear implant. Dorling Kindersley/Getty Images

What do you get what you combine the low-frequency acoustic amplification of a hearing aid with the high-frequency sound access of a cochlear implant? You get what is called a hybrid cochlear implant. The hybrid cochlear implant is a surgically implanted device with an external sound processor that works with the cochlear implant portion of the device and serves as a hearing aid for low-frequency hearing loss.

How Does It Work?

Microphones on the external sound processor pick up sounds, and those sounds are converted to digital information. These sounds are transmitted directly to the electrode array in the cochlea.

At the same time, the acoustic/hearing aid portion picks up the low-frequency sounds, amplifies them, and those sounds are transmitted through the ear canal to the ear drum and inner ear.

The cochlea picks up the sound information from both sources and sends them to the brain which makes sense of what is heard.

Who Is a Candidate?

The hybrid cochlear implant is approved for unilateral (one ear) use in people age 18 years and older who:

  • have residual low-frequency hearing and
  • severe to profound high-frequency sensorineural hearing loss with
  • limited benefit from appropriately fit hearing aids.More specifically, low-frequency hearing should be from normal limits to moderate hearing loss (better than 60dBHL).Mid to high frequency hearing in the implant ear should have an average of greater than or equal to 75dBHL for 2000, 3000, and 4000Hz. In the opposite ear, that average should be greater than or equal to 60dBHL.

Other Contraindications

According to the Nucleus Hybrid Guidelines, you are not a candidate for this implant if your deafness is due to lesion(s) of the acoustic nerve or central auditory pathway, have active middle ear disease (with or without a hole in the eardrum), have no cochlea (inner ear), or have had severe to profound hearing loss for 30 years or longer.

Low-Frequency Sounds

In this case, low frequencies are considered to be sounds measured up to and including 500Hz. Low frequencies include vowel sounds, like “ah” and “oo”. They provide the rhythm and melody of speech and convey volume information. Examples of low-frequency sounds are thunder, a bass drum, or a man’s deep voice.

High-Frequency Sounds

High frequencies add clarity and crispness to sound quality. Consonant sounds, such as “s” and “f” contribute to speech understanding. Examples of high-frequency sounds include bells, birds chirping, and whistles.

Benefits of a Hybrid Cochlear Implant

The hybrid cochlear implant allows those who were not previously candidates to benefit from the high-frequency detection of sounds not possible with a hearing aid while not sacrificing residual low frequencies in the cochlea due to the shorter electrode array. Users also report more satisfaction with speech in noise and music sound quality with the hybrid implant versus hearing aids alone.

Disadvantages of a Hybrid Cochlear Implant

A surgical procedure is necessary for placement of the cochlear implant, and that carries risks associated with infection and anesthesia. Once the implant is placed, certain medical procedures such as MRI and electroconvulsive therapy can not be done. Head trauma may damage the implant. Sound quality may be intermittently distorted when around certain sources of interference, such as security systems, mobile communication equipment, and some 2-way radios. It should also be noted that this is fairly new technology, and there is limited long-term data available on users.

For more information, or to find out if you are a candidate, contact your audiologist.

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