Cochlear Implants -An introduction

R.RanjithAudiologist

Madras ENT Research FoundationChennai

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What is a cochlear implant ?

• A cochlear implant is a hearing prosthesis designed to restore or provide a level of auditory sensation to adults and children who have a severe to profound bilateral sensori-neural hearing impairment and who get limited benefit from hearing aids

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Parts of CI

• External

• Microphone• Speech Procressor• Transmitting coil

• Internal• Receiver /Stimulator• Electrode array

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The Cochlear Implant in situ

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Electrode Array in the Cochlea

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Sound is Sound is received by the received by the microphonemicrophone

MicrophoneMicrophone

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Sound is sent Sound is sent from from microphonemicrophone to to speech speech processorprocessor

cablecable

Speech Speech processorprocessor

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Speech Speech processorprocessor analyzes and analyzes and digitizes the digitizes the sound into sound into coded coded signalssignals

SpeechSpeechProcessorProcessor

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Coded Coded signals are signals are sent to the sent to the transmitting transmitting coilcoil

Transmitting coilTransmitting coil

CablesCables

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Transmitting Transmitting coilcoil sends the sends the code across code across the skin to the the skin to the receiver/ receiver/ stimulatorstimulator of of internal internal implantimplant

Transmitting coil

Receiver/ stimulator

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Signals are Signals are sent to the sent to the electrodeselectrodes to to stimulate the stimulate the remaining remaining nerve fibresnerve fibres

electrode

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Signals are Signals are recognized recognized as sounds by as sounds by the brain the brain producing a producing a hearing hearing sensationsensation

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• 1985: First children implanted

with Nucleus multichannel

cochlear implant in

Melbourne.

• Over 50,000 children have been implanted and the age of implantation has dropped significantly.

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Selection criteria - Children

• Twelve months of age or older• Bilateral severe to profound sensori- neural

hearing loss - congenital or acquired• No or less benefit with the most optimised

hearing aid• Aided audiometric thresholds that fall outside

speech range at 2kHz• No medical or radiological contraindications• Motivation and good family support.

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CandidacyGuideline Audiograms

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Selection Criteria - Adults

• 18 years of age or older

• Profound, severe-profound, bilateral sensorineural hearing loss

• Post lingual onset of profound deafness

• Little or no benefit from hearing aids

• No medical or radiological contraindications for surgery

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Factors that may exclude candidacy

• Absence of auditory nerve or lack of auditory nerve integrity bilaterally

• Neurological damage impeding auditory processing

• Medical risks of surgery that exceed the expected benefits of the cochlear implant

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Factors that may influence outcomes with an implant

• Length of profound deafness• Age at implant• - 0 to 5yrs optimal• - 5 to 7 yrs Results will vary• -7yrs and above provided good HA use and • re/habilitation• Aetiology• Use of hearing aids prior to implantation• Amount and quality of re/habilitation before and after implant• Family support and commitment• Educational methods and communication mode

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The process of getting an implant

Pre surgery:

• Initial Referral• Full medical evaluation• Full audiological evaluation to assess level and type of

hearing loss (PTA.Impedance,ABR,ASSR,OAE and Prom-Stim)• Optimal hearing aid fitting and evaluation• Hearing aid trial and auditory training• Post training evaluation• Counseling of parents and family members• Acceptance for implant and final counseling

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The process of getting an implantThe process of getting an implant

Surgery:• 3 to 5 hours• 1 to 2 day hospital stay• 3 to 4 weeks later – switch on

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X-Ray of Cochlear Implantin Situ

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Neural Response Telemetry System

Transmitter

ReceiverDecoderCurrent Source

TransmitterEncoderAmplifier

ReceiverPCI

IF5 Card

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Stimulation and Recording Modes

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Stimulation

Recording

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Post Surgery: Fitting the externals

Switch on• About three weeks following

surgery the implantee will return to the clinic to have the external parts of the device fitted

• This first fitting is called the ‘switch on’ or ‘tune up’ of the device

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Clinical Programming SystemCPS

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What is involved in activating the system?

• the term referred to as MAPping/programming

• the procedure required for fine tuning the device to suit each individual’s hearing needs

• requires specialised software and programming interface systems to program the speech processor.

• Is the process of measuring and controlling the amount of electrical current delivered to the cochlea. To provide the patient with comfortable and useful hearing sensations.

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Listening training pre and post implant (AVT)

• Listening training• An individual program is worked out for each recipient• Focus is on listening• For children: Listening training follows normal child speech and

language developmental milestones – hearing age vs chronological age

• Family must be involved• With children the parent is trained to carry over listening to home

– in a natural environment

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The Cochlear Implant Team:Core members

• The Parents• Need to be involved in all evaluation processes and decisions.

Must have realistic expectations and fully understand all aspects of process.

• The Surgeon• Full medical and surgical evaluation, counseling, surgery and

post surgical care

• The Audiologist • Full audiological evaluation, hearing aid fitting, counseling,

mapping, adult rehabilitation and ongoing follow up

• The Teacher of the Deaf/ Habilitationist• Pre and post surgery listening training, full habilitation program

planning for individual and full home training program for parents

Audallion beam former

Brain Stem Implants

Espirit 3 G speech processor

Neural response telemetry - NRT

Newer developments

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• Completely implantable Implants

• Neuronal regeneration factors

• Improved speech coding strategies

• Automated Mapping based on NRT

Future