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Cochlear Implant Cochlear Implant

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					Cochlear Implant

 Prof. Hamad Al Muhaimeed
The Fundamental Concept of
     Cochlear Implant


  To bypass the damaged hair
  cells.
                   History:

• Old generation: Sound awareness only
• New generation: Improved communication
      abilities (auditory cues with lip reading, open
      set speech)
• Since 1972 more than 16 different cochlear implants
• 1984 FDA approval for adults
• 1990 children approval
Anatomy   Anatomy
Anatomy
Scala tympani
Scala vestibuli
Cochlear duct
Basilar membrane
Vestibular membrane
Tectoral membrane
Hair cells (outer/inner)
Cochlear nerve fibers
Anatomy-micro
Physiology of Hearing
Anatomy
     Sensorineural Hearing Loss
Death of hair cells vs. ganglion
cells
Otte, et al estimated we need
10,000 ganglion cells with 3,000
apically to have good speech
discrimination
Apical ganglion cells tend to
survive better (?acoustic
trauma)
Central neural system plasticity
Pathologic Anatomy
       Anatomy of Speech
Mix of frequencies
Speech recognition is “top-down” process
Formant frequencies: frequency maximum
based on vocal tract
F0 is fundamental frequency
F1 & F2—contribute to vowel identification
F3—l,r (lateral and retroflex glides)
F4 & F5—higher frequency speech sounds
Some speech based on amplitude—k, f, l, s
Structure of Cochlear Implant



  1. External components
  2. Internal components
Components of Cochlear Implant
    Types of Cochlear Implants
Single vs. Multiple channels
   Audio example of how a cochlear implant sounds with
    varying number of channels
Monopolar vs. Bipolar
Speech processing strategies
   Spectral peak (Nucleus)
   Continuous interleaved sampling (Med-El, Nucleus,
    Clarion)
   Advanced combined encoder (Nucleus)
   Simultaneous analog strategy (Clarion)
Anatomy of a Cochlear Implant
How does it work?
Neural Responses to Sound


1. Temporal coding: Provide information
   about timing cues (rhythm and intonation.
2. Place coding: Rely on the tonotopic
   organization of a neural fibers.
3. Provide information about quality (timber
   of a speech signal – sharp to dull)
      Site of Stimulation


1. Extracochlear
2. Intracochlear
3. Retrocochlear (lateral recess of the
   fourth ventricle over the cochlear
   nuclei.
                Stimulus

a. Stimulus type:
     - Analog (continuous)
     - Digital (pulsatile)
b. Stimulus configuration
     1. Bipolar – localized site of stimulation
     2. Monopolar – stimulates large
        population of neurons
         Speech Coding


As speech is produced, the mouth, nose & pharynx
modify the frequency spectrum so that peaks and
formants are produced at certain frequencies.
Speech processing used – 3 formants:
      F0 = 100 to 200 Hz
      F1 = 200 to 1200 Hz
      F2 = 550 to 3500 Hz
  Number of Channels


1. Single channel – no place
   coding
2. Multi channel
       Stimulation Mode


1. Simultaneous: More than one
   electrode is activated at a given
   succession - CIS
2. Sequential: A continuous series of
   electrode activates in succession -
   speak
 Electrode Design

1. Single electrode
2. Multielectrode
Indication for Cochlear Implant
Adults
   18 years old and older (no limitation by age)
   Bilateral severe-to-profound sensorineural
    hearing loss (70 dB hearing loss or greater
    with little or no benefit from hearing aids for 6
    months)
   Psychologically suitable
   No anatomic contraindications
   Medically not contraindicated
      Indications for Cochlear
      Implantation -- Children
12 months or older
Bilateral severe-to-profound sensorineural hearing loss
with PTA of 90 dB or greater in better ear
No appreciable benefit with hearing aids (parent survey
when <5 yo or 30% or less on sentence recognition
when >5 yo)
Must be able to tolerate wearing hearing aids and show
some aided ability
Enrolled in aural/oral education program
No medical or anatomic contraindications
Motivated parents
     Factors Affecting Patient
            Selection

a.   Onset of deafness (congenital or adventitious)
b.   Year of deafness
c.   Length of sensory deprivation (i.e. no hearing aids)
d.   Socioeconomic factors
e.   Educational level
f.   Individual ability to use minimal cues
g.   General health
Factors Affecting Pt. (cont.)

h. Personality
i. Willingness to participate in rehabilitation program
j. Language skills
k. Appropriate expectations
l. Desire to communicate in a hearing society
m. Psychological stability
n. Cochlear patency
    Audiologic Evaluation


1. Pure tone audiometry under headphones
2. Warble tone audiometry with a hearing aid
   in a monitored free field
3. Immittance testing
4. Speech recognition testing
5. Speech awareness testing
Audiologic Evaluation (cont.)


6. Environmental sounds (closed and open set)
7. Speech reading (lip reading) ability
8. Electrical response audiometry
9. Auditory discrimination
10.Transtympanic electrical stimulation
   (promontory or round window test)
         Medical Evaluation

1.   Clinical history and initial interview
2.   Preliminary examination
3.   Complete medical and neurologic examination
4.   Cochelar imaging using computed tomography
     (CT or magnetic resonance imaging (MRI)
5.   Vestibular examination (electronystagmography)
6.   Pathology tests
7.   Psychologic or psychiatric assessment or both
8.   Vision testing
9.   Assessment for anesthetic procedures
CT Findings
           Contraindications

Incomplete hearing loss
Neurofibromatosis II, mental retardation, psychosis,
organic brain dysfunction, unrealistic expectations
Active middle ear disease
CT findings of cochlear agenesis (Michel deformity) or
small IAC (CN8 atresia)
Dysplasia not necessarily a contraindication, but
informed consent is a must
H/O CWD mastoidectomy
Labyrinthitis ossificans—follow scans
Advanced otosclerosis
            Surgical Procedure

All electrode insertions are carried out through the facial
recess approach. Various incision designs are used to
allow wide exposure of the mastoid and squamous
portions of the temporal bone. The temporalis muscle
and periosteum are widely stripped to accommodate a
“table” for the pedestal of the Ineraid device or the
receiver-stimulator of the other devices. The
mastoidectomy is not widely saucerized, but instead
overhanging ledges are purposefully maintained. Care
must be exercised so as not to damage the fibrous
annulus during the facial recess approach..
Surgical Technique
         Complications:


A. Intraoperative

   1. Intraoperative cannot be placed
       appropriately.
   2. Insertion trauma
   3. Gusher
     Complications (cont.):

B. Postoperative
   1. Postauricular flap edema, necrosis or separation
   2. Facial paralysis
   3. Transient vertigo is more likely to occur on a
      totally nonfunctioning vestibular system.
   4. Pain is usually associated with stimulation of
      Jacobson’s nerve, the tympanic branch of the
      glossopharyngeal nerve.
   5. Facial nerve stimulation
   6. Meningitis
   7. Device extrusion
             Rehabilitation

  Tuning or mapping of the external processor to
meet individual auditory requirements after 3 - 4
weeks postop.
   1. Multisensory approach
   2. Bimodal stimulation
   3. Suprasegmental discrimination training
   4. Segmental discrimination and recognition
       training
   5. Speech tracking
   6. Counseling
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
Rehabilitation
        Pediatric Implantation

Five years after approval was given for adult
implanta-tion by FDA, approval of cochlear implants
for use in patients ages 2 to 17 years was granted. The
major concerns regarding implantation in children
included difficulty in evaluating the young child’s
hearing impairment, assessing the performance and
effect of implantation on the child’s development
compared with traditional types of training, the risks
of implantation (both intraoperative and long term),
the effects of implantation on the auditory system, and
the challenges of effectively programming such
sophisticated devices in children.
Auditory Brain Stem
Any Question ?

				
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posted:7/22/2011
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