20. Types and indications of hearing aids. Cochlear implantation

What are the principles of hearing aids

• amplify sound

• conductive HL- better treated with surgery

• significant HL- better treated with cochlear implantation

What are the indications

• Hypoacusis → partial or total inability to hear

• When there is no satisfactory medical/surgical treatment

• When patient prefers it over surgical treatment

• When speech audiometry of < 80% corrected responses at 65 dB SPL

What are the components of hearing aids

• microphone

• amplifier

• speaker

• energy source

• signal processing can be analog or digital

What factors do the choice of hearing aids depend on

• severity of hearing impairment

• cause of hearing impairment

• anatomical variability of auditory canal

• physical and mental skills of patient

• financial status

What are the types of hearing aids

• behind the ear- BTE

• In the ear- ITE

• in the canal- ITC

• completely in canal- CIC

• Bone anchored hearing aids- BAHA

• Contralateral routing of signals- CROS

• body worn

• open fit

Describe BTE hearing aids

• mild to severe hearing loss

• widespread use

• becoming less used due to newer ITE

• only type that can be used for small children

describe ITE hearing aids

• mild to severe hearing loss

• placed in concha

describe ITC hearing aids

• from mild to severe HL

• placed deeper within ear canal

• sound localisation is better

• noise created by wind is smaller

• cosmetically better

• can cause accumulation of ear wax

• not suitable in ear discharge

Describe CIC hearing aids

• placed deeply in ear canal

• only available for mid- moderate hearing loss- amplification limited

• most cosmetic- completely unseen

• no wind noise

• small battery requires removal with special tools

describe BAHA hearing aids

• attached to the skull

• surgically implanted hearing aids based on bone conduction

• used in CHL and mixed hearing loss who cannot wear conventional hearing aids

• has titanium implant, abutament and sound processor

• sound processor transmits vibrations through external abutment to titanium implant then directly to cochlea

Describe CROS hearing aids

• for unilateral hearing loss

• mostly replaced by wireless systems- eg BAHA

• takes sound from ear with poorer hearing and transmits it to ear with better hearing

Describe body worn hearing aid

• completely outdated, bad sound localisation, wind noise

• microphone and amplifier within a box worn around neck or in pocjet

• amplified sound through cord into speaker within auditory canal

describe open fit hearing aid

• placed in case behin d the ear and connected via tube and a soft tip to ear canal

• smaller than standard BTW- almost invisible

• advantageous in higher frequency hearing loss with normal low frequency hearing

  • high frequency sounds are amplified or enhanced better

What are cochlear implants

• subcutaneously implanted device that transforms sound waves into electrical impulses that directly stimulate the vestibulocochlear nerve with intracochlear electrodes

• in children- best results are obtained when implantation is before 1 year due to early brain plasticity

• requires functional auditory nerve

What are the indications for cochlear implants

• hearing loss that cannot be treated with hearing aids

• patients with complete or almost complete deafness due to absence of cochlear function → usually SNHL caused by no or few hair cells

how does a cochlear implant work

• microphone worn in ear receives sound and transmits it to speech processor worn on skull → transforms acoustic signal to electrical

• transmitting coil behind ear transmits the electrical impulses as radio frequencies through the skin to implanted cochlear receiver that stimulates auditory nerve

What are implantable hearing aids

• Bone anchored hearing aid

• middle ear implants

Describe middle ear implants

• implanted to one of the small bones in middl ear

• used in patients with CHL, SNHL, mixed hearing loss

• amplifier implanted under skin→ sound waves into electrical impulses

• converted into mechanical vibrations in transducer

• vibrations are transmitted directly to ossicles or cranial bone