Hearing Aids

Question 1

What is the goal of HAs and is this goal met?

Answer 1

• to amplify sounds
• provide audibility
• only an aid and not a cure for hearing loss
• 1 in 6 have hearing loss and 1 in 10 would benefit from HAs

Question 2

Types of hearing aids

Answer 2

• Behind the ear (BTE)
• Post-aural
  These are worn behind pinna
  Coupled to concha via plastic tube and ear mould
  Delivers sound to ear canal
• In the ear (ITE)
  More restricted acoustics but better aesthetic

Question 3

What are bone conduction (BC) hearing aids?

Answer 3

• Sound transmitted through mechanical vibration of cranial bones –> to cochlea rather than through outer/middle ear (bypasses these for conductive losses)

Question 4

Issues with BC HAs

Answer 4

• Cosmesis of headband
• Headband discomfort (headaches, pressure)
• Restricts movement
• Low gain, poor sound quality and speech discrimination
• Acoustic feedback

Question 5

What are bone anchored HAs?

Answer 5

• Same transmission as bone conduction but bone vibrator implanted directly into Pt
• titanium screw inserted into skull
• aid attached to screw
• for pts with chronic conductive hearing loss/outer/middle ear pathology

Question 6

HA components

Answer 6

• Microphone (converts sound energy into electrical energy)
• Receiver (converts electrical energy back into sound)
• Digital amplifier (signal sampled at discrete time intervals and processed as discrete quantities)

Question 7

HA physical fit

Answer 7

• ear mould provides interface between HA and user
• facilitates efficient transfer of sounds from receiver to the external auditory meatus
• physical features can significantly affect the electroacoustic of HA

Question 8

What are the features of a good ear mould?

Answer 8

• comfortable
• easy to fit and remove
• cosmetically acceptable
• easy to clean
• good contact for acoustic fit

Question 9

What are the problems associated with a poor fitting ear mould and what can be done to fix it?

Answer 9

• Causes hurt
• Check Pt is inserting earmould correctly
• Make new one
• Shave off parts of earmould

Question 10

What are the problems associated with a acoustic feedback and what can be done to fix it?

Answer 10

• Usually translates as whistling
• Feedback caused by amplified sound escaping from the ear and is re-amplified by HA
• Check mould fit and makes contact with ear
  > make new softer mould of greater contact
• increase feedback suppression parameter
• turn down gain slightly

Question 11

What are the problems associated with a wax and what can be done to fix it?

Answer 11

• Wax blocks ear mould and stops/reduces amplified sound being presented to ear
• wash mould or remove wax

Question 12

What are the problems associated with condensation and what can be done to fix it?

Answer 12

• Blocked tubing-condensation in tube
• Insert small vent into air mould to improve air circulation
• replace tubing

Question 13

What are the problems associated with sweat and what can be done to fix it?

Answer 13

• Some users complain of blocked, sweaty ear canals

- narrow bore vent into mould to allow better air circulation

Question 14

What are the problems associated with loudness/sound/etc and what can be done to fix it?

Answer 14

• Aid too loud
  > reduce overall gain below recommended levels
  > once Pt has acclimatised then increase
• Aid too noisy
  > reduce low frequency gain
  > add vent to mould
• Aid too tinny
  > reduce high frequency gain
• Problems with background noise
  > program HA to allow for directional microphone and increase noise reduction algorithm strength