Types of Hearing Aid

Look at the images below and answer the questions that follow. 

A
A
B
B
C
C

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What device is in image A and label parts A-E.

This is an image of a behind ear hearing aid.

The labelled parts are as follows:

A) Mould

B) Connection tube

C) Battery

D) On off switch

E) Pull cord

Name two complications of wearing A?

 

  • Otitis externa

  • Wax build up

  • Skin irritation

State 2 causes of whistling whilst wearing this device.

Wax build-up and loose fitting

Name 2 indications for B.

  • Permanent bilateral conductive or mixed hearing loss 

  • Bilateral conductive or mixed hearing loss where one ear works better than the other, but clinicians would have considered two air conduction hearing aids (ACHAs) if the type of hearing loss had not precluded their use.

  • Unilateral conductive hearing loss with ear canal stenosis that is unlikely to benefit from meatoplasty; or who have had revision surgery and failed to tolerate ACHA.

  • Profound unilateral sensorineural hearing loss

For all must also be clinically unsuitable for other medical or surgical treatments. 

Ref: https://www.england.nhs.uk/wp-content/uploads/2013/04/d09-p-a.pdf 

Name two complications with B.

  • Abutment site problems – loosening

  • Skin infection

  • Skin overgrowth

  • failure to osseointegrate

  • Discomfort/pain

What is C?

Cochlear implant

Describe the audiological criteria for consideration of implanting C ?

  • According to the 2019 NICE Cochlear implants for children and adults with severe to profound deafness guidelines. Cochlear implantation is indicated if have severe to profound deafness is defined as hearing only sounds that are louder than 80 dB HL (pure-tone audiometric threshold equal to or greater than 80 dB HL) at 2 or more frequencies (500 Hz, 1,000 Hz, 2,000 Hz, 3,000 Hz and 4,000 Hz) bilaterally without acoustic hearing aids. 
  • Adequate benefit from acoustic hearing aids is defined for this guidance as: >50% phoneme score or greater on Boothroyd word test presented at 70 dBA for adults. For children, speech, language and listening skills appropriate to age, developmental stage and cognitive ability.

Ref:  https://www.nice.org.uk/guidance/ta566

Supporting Documents

Hearing aids- All have 4 components:

  1. Microphone
  2. Amplifier
  3. Sounds transmitter
  4. Power source

Hearing aids process external sounds and present them to the inner ear in a way that can be interpreted by the brain. They can be:

  • Analogue – can reduce unwanted peaks. 
  • Digital – processing can adjust signal to selectively increase certain frequencies/decrease background noise

There are many types:

  1. Postauralbehind the ear – and have an induction coil that can be used to pick up sound from TV or theatre. 

Hearing aid is made of acrylic and may whistle when microphone is too close to speaker or there is lots of wax in the ear.

TMO switch– telecoil for induction loop, microphone for general use, off

  1. In-the-ear aids– smaller, more expensive than the above. They are prone to auditory feedback- picking up sounds they make causing a whistling. 
  2. Body-warn aids– bigger, and more cumbersome but better sounds
  3. Bone conduction aids– vibrator strapped to skull
  4. Osseo-integrated aids/BAHA– implant in skull, external transmitter. 
  5. Implantable middle ear aids- an external transmitter vibrates a receiver attached to incus, round wind or stapes head. 
  6. Cochlear implants- an array is implanted into cochlea which is thought to stimulate the auditory nerve directly. Sounds are picked up behind the ear and processed using speech decoding. The array is stimulated by induction. 

For cochlear implants careful selection–>neural plasticity is key-

  1. If sound not heard by 8 months after birth they cannot hear
  2. If speech is not heard by 3 years articulation is not possible
  3.  

For cochlear implants the patients must be Postlingually deaf. i.e. have speech before they became deaf. 

MDT assessments before cochlear implant– psychiatric, MRI, audiology, disease free ear. 

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