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The ImplantThe history of Cochlear implants is a little confused, as different nations and scientist compete for the honour of invention. However, we know that the first person to know that electricity stimulates the ear was Volta, in 1800. Volta actually tried this on himself, but it hurt, so he stopped experimenting on his own ears! One story runs that the first cochlear implant was a single channel one, implanted in California in the 1960s (although the French claim to have been experimenting in the 1950s). The first really wearable processor was in 1972. The first child implant was in 1980. The first wearable multi-channel implant was developed in Melbourne in 1982, and the first one in Britain was in 1990. Accounts of dates and places may differ, but this is the story. The youngest child ever to receive an implant is 14 months. (In the next session, we will discuss the ethics of this). People were only selected for an implant previously if they scored zero on a speech recognition test (without lip-reading). Now, some hospitals will implant someone who scores up to 20% on these tests. Again, we might want to consider the ethical and social implications of this sliding scale of people who "need" implants. Less controversially, the cochlea must also be suitable for an implant. If it is badly malformed, or not there, then an implant is no good. Meningitis often causes bone to grow in the channels of the cochlear, so some people who are deaf through meningitis may not be suitable. However, in some cases, the bone can be drilled out. Most adults who are referred for an implant are considered suitable, but only about 50% of the children are. Implantees can be up to eighty years old or over. So long as a person can cope with the anaesthetic, and will benefit from the implant, surgeons will implant. (Even people with terminal illnesses have had implants) The operation is usually about four hours, although it can last for up to six hours if there are problems like an ossified cochlea. The surgeon makes a large incision behind the ear and drills into the mastoid bone, taking care to avoid cutting the facial nerve just behind the ear canal, and enters the cochlea at the lowest (basal) turn. Because many people now still have some residual hearing, a new technique called "soft surgery" is used. This uses a special gel to stop the cochlear fluid (essentially brain fluid) leaking out and so damaging hearing any further. Going into the base of the cochlea also helps save residual hearing because much of the residual hearing is at the topmost coil. Surgeons need to be careful to damage the cochlea as little as possible. A child of two receiving an implant might have several more as technology changes throughout their life. If we think how far we've come over the last 80 years, think how far technology might progress in the next 80 years. Surgeons would be very unpopular if they ruined chances for improvement in the future. All through the operation there is a drip feeding antibiotics into the brain to prevent infection that could lead to meningitis. Just before the surgeon stitches the patient up again, they put a small electric current through the implant. If the stapedial muscle contracts (remember the stapedial reflex?), they can be sure it is working. In the past, surgeons have accidentally put the implant into the semi-circular canal by mistake, and only noticed three days later with an X-ray. They used to make adults lie absolutely still for 48 hours after the operation, in case any brain fluid leaked out. Now this has changed, since they were unable to make small children stay still, and they have found that there are no leaks. (One shudders to think what would have happened if they had been unable to keep a toddler still for 48 hours, and the brain fluid had leaked....). |
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