Sunday, March 15, 2009

Cochlear Implants-What they look like and how they work

Cochlear Implants - Surgery

With Ava's surgery just over two weeks away (two long weeks that is!), many of you are wondering just what exactly will be done to Ava? Last month I came across a webcast of a live surgery of a little boy receiving his second cochlear implant. The webcast is about 1 hour long. The surgery is narrated by the surgeon in real time as well as the audiologist who gives a description of the implant and how it works. WARNING-the webcast is graphic so if you have a weak stomach then I recommend you do not watch it. If you do watch it, you will be amazed at how miraculous the technology really is.

In the US, I believe the surgery is an outpatient procedure. However here in Toronto the patients are kept in the hospital overnight and discharged the next day.

The small incisions take about 3-4 weeks to heal. At around 3 weeks post-op, we will be given all the external equipment as well as equipment instruction. Ava is to wear the equipment not yet activated for one week to get used to having it on. At around 4 weeks post-op, we will see the audiologist who will then "activate" the cochlear implants and Ava will hear for the very first time! We will be sure to videotape this activation for all to see. Some babies react to the sudden onset of overwhelming sound by crying (which is a good thing because that means they can hear!), some babies don't react much at all at first. This is all very exciting, however, the fact is that once the equipment is activated, it is going to take a few years of weekly auditory verbal therapy for Ava to make sense of sound, to give it meaning and develop language. Essentially, Ava's hearing will be that of a hearing newborn baby once she is activated. She will have to play catch up so that by the time she enters kindergarten she will be even with her hearing peers in terms of speech and language. She has a head start because she is being implanted at such a young age. The rate of success of catching up to her peers is high and quicker than those implanted at a later age. It will take hard work , perseverance and patience. Ava is so lucky to have 5 siblings at home to constantly bombard her with language. We can see she wants to communicate so very much as she is always studying the movement of our mouths while we talk and seems puzzled by it.
How do cochlear implants work?

In normal hearing, sound moves in the ear canal and strikes the eardrum. The soundwaves cause the eardrum to vibrate which move the inner ear bones which in turn cause the fluid in the inner ear to move the hair cells inside the cochlea. The hair cells convert this movement into electrical impulses which are sent to the auditory nerve into the brain thus the brain perceives sound. In sensorineural hearing loss, the hair cells inside the cochlea are damaged therefore the brain doesn't receive sufficient electrical impulses. In persons with mild, moderate to severe hearing loss, such as mine and daughter Lauren's, hearing aids are sufficient to amplify the sounds so that the remaining hair cells can still be stimulated and do their job. In Ava's case however, the hair cells are too damaged or missing altogether so hearing aids cannot help her.
A cochlear implant consists of an internal component and external components. When Ava has her surgery, the surgeon will be placing the internal component, which is a receiver/stimulator that is positioned under the skin in a bed created in the bone behind the ear. An electrode array, consisting of 22 tiny electrodes is surgically inserted approximately one inch into the cochlea.
The external components, which will be on the outside of the head, consist of a light-weight sound/speech processor (resembles a hearing aid) composed of a directional microphone worn behind the ear and a transmitter which is placed over the spot where the implanted receiver is located and held in place by a magnet.

How it works - the external sound/speech processor (which is the device behind the ear that looks like a hearing aid) captures sound and converts it into digital signals. The processor sends the digital signals to the internal implant which is under the skin behind the ear. The internal implants converts the signals into electrical energy, sending it into the electrodes inside the cochlea. The electrodes directly stimulate the auditory nerve bypassing the damaged hair cells and the brain perceives these signals as sound.
What does it look like?

This is what the external components look like. Because Ava's ears are so small, the sound processor is too heavy to stay on her ears. The processor can be separated so that the microphone part, which is lighter, can stay on her ears while the bottom half which is the controller and holds the batteries can be pinned to her clothes or inserted into pockets I will have to sew on or inside her shirts (more like a job for Ava's grandmothers I can barely sew a button). When Ava is about 2 years old or so, her ears should be able to support the full weight of the sound processor and controller (BTE or behind the ear).

Below is a link showing a diagram of Ava's external components. We will be able to choose what colour we want to use - probably dark brown to match her hair.

I hope I have given a somewhat accurate description of the surgery and components of the cochlear implant. If you come across this blog and note any inaccuracies, please leave me a comment so that I may fix them.


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