Aural Rehab: Cochlear Implants pt. 2

CI Size

same for babies and adults

Cochlea formed by…

25 weeks gestational age

ossicles are fully formed at…

birth

pinna, middle ear, and ear canal continues to grow until age…

7 yo

• different resonant properties

cochlea is the size of a …

frozen pea

CI’s encode what well?

time and temporal cues

electrical stimulation can mimic time _.

WELL

why do CI’s encode time well?

electrical stimulation from impact can mimic well by adjusting the pulse rate of the electricity (using electrical pulses at various rates)

The VIII CN can interpret these timing cues _.

WELL

CI timing works very well because of …

nature of the electricity, pulse rates, and VIII CN to pick up and fire action potential

Implants job is done after

the VIII CN gets the electrical information

CI replaces what parts of the ear

• outer ear

• middle ear

• cochlea

CI’s have a more difficult time encoding what

• frequency resolution

• discrimination

• pitch

why does the CI have a hard time encoding frequency?

• electricity current can be spread because of fluids in cochlea which can activate different parts of the basilar membrane

• less electrodes compared to normal outer and inner hair cells (thousands of hair cells compared to 22 electrodes, and 2 ½ turns compared to 1 ½ = less stimulation of basilar membrane)

• channels can interact among adjacent neural populations

how many outer hair cells?

12,000

how many inner hair cells?

3,500

Channel

• the implant processor divides sound into frequency bands

• each band is assigned to an electrode (hope is one band per electrode) or group of electrodes

• the band is a channel

• greater number of channels → greater frequency resolution

the band is a _.

CHANNEL

greater number of channels →

greater frequency resolution

channels attempt to mimic what

tonotopic organization of the basilar membrane

are the number of channels equivalent to the number of electrodes?

not always

why might the number of channels not equal the number of electrodes?

• electrode placement

• cochlear anatomy

• surgical complications

Current Steering (by Advanced Bionics) does what?

helps with frequency resolution problem

• instead of assigning one channel to one electrode, it works in pairs of electrodes

  • sends more current to one and less to the other to steal current between the pair

some of the patients success with a CI is dependent of what?

surviving spiral ganglion cells

first CI’s only had how many channels?

1

Today how many channels do CI’s have?

22

what part of music can a CI pick up?

rhythm (beats/tempo)

CI candidacy historically

• severe to profound hearing loss

• very poor discrimination even with aids

• monaural implantation

CI candidacy today

• depends on many factors,, not use hearing loss

• auditory neuropathy spectrum disorder

• binaural impantation

• single sided deafnessl

auditory neuropathy spectrum disorder

dysfunction of the VIII CN

• does not fire synchronously

• spectrum (lot or little dysfunction)

Advanced Bionics candidacy

• moderate to profound HL

• WRS = <60%

• trouble communicate in noise, distance, quiet

• avoid social acitivites

• unsatisfied HA user

60/60 rule

• <60% on WRS

• >60 dB HL PTA

  • suggest go through whole evaluation

Cochlear Americana’s Candidacy

• adults

  • moderate to profound sensorineural HL in both ears

    • bc of how electrode array does not go to the apex (low frequencies)

  • limited benefit form HA <50% sentence recognition

• children (2-17yo)

  • severe to profound

  • limited benefit form binaural HA

  • tests

• children (9-24 mo)

  • profound HL

  • limited benefit form HA

Do CI help conductive hearing loss?

no

off label

not FDA approved

Hybrid Device

hearing aid and CI

• low frequency amplification through HA

• high frequency amplification through CI

CI Process: Prior to Implantation

• rule out outer and middle ear infections

• hearing assessment - all plus speech

• trial use of HA - couple months

• CT and MRI of middle an inner ear structures

• psychological exam

• physiological exam - anesthesia prep

CT and MRI are look at what ear structures?

middle and inner ear structures and VIII CN

CI Process: during surgery

• shave scalp/clean area

• intravenous and monitoring equipment

  • VII CN monitor

  • neural response telemetry testing

Monitor what CN during CI surgery?

VII (facial nerve)

• runs right next to the ear canal

facial stimulation

when the electrode ends up stimulating the facial nerve

neural response telemetry

• sort of like ABR

• measures the electrical evoked compound action potential of VIII CN

CI Process: surgery

• incision behind the ear through the mastoid bone leading to the middle ear space

• opening made in the cochlea implant device or insertion uses the round window

• electrode insertion with stylet → when removed it curls

• implant in place

electrode array is inserted with

stylet

CI Process: post surgery

• healing for 3-6 weeks

• first fitting one by audiologist

• multiple follow up appointments

CI heals for how long?

3 to 6 weeks

what happens at an the first fitting and who does it?

• initial stimulation

• impedances

  • measure of resistance of electricity

• mapping

• audiologist

what happens at follow up appointments

• mapping

• testing of implant integrity

• channel manipulation

• testing of hearing function with implant

what kind of impedance do you want?

low

what kind of impedance do you not want, why, and causes?

• high

• resists flow of electricity

• cochlear fluids, cell structure, inflammation, movement

• less electrodes active

what is mapping

• programming

  • determines how much electricity to deliver

    • voltage, pulse (rate and width)

    • frequency bands and channels determind

first audio logic testing done

ling six