Download Hearing Disorders

Hearing Disorders
Properties of Sound
• Intensity = loudness
– Unit of measure is the decibel (dB)
• Frequency = pitch, number of vibrations
per second
– Unit of measure is Hertz (Hz)
• Duration = time
– Unit of measure is seconds (s)
The Auditory System
Peripheral Auditory System (PAS)
The Auditory
System
Central Auditory System (CAS)
PAS: Outer Ear
• Auricle/Pinna
– Localisation
PAS: Outer Ear
• Ear Canal
– Funnels
sound
• Cerumen
PAS: Middle Ear
• Tympanic Membrane
– Amplifies
• Ossicular Chain
– Amplifies
• Eustachian Tube
– Equalises
The Eustachian
Tube
PAS: Inner Ear
PAS: Inner Ear
• Cochlea
– Hearing
• Vestibular Apparatus
(SemiCircular Canals)
– Balance
Physiology of the PAS
Central Auditory System
• Auditory Nerve
•30,000 fibres from
Cochlea
• Brain Stem Nuclei
•“cross-over point”
• Auditory Cortex
(Temporal Lobe)
Process of Hearing
Audiometry
The measurement of hearing
Testing the PAS: Air Conduction
• “Pure” tones at
various frequencies
(Hz) and loudness
levels (dB) are
presented.
• Determination of air
conduction
“threshold.”
Air Conduction Testing
Testing the PAS: Bone Conduction
• “Outer & Middle ears
are “bypassed” to
test Inner Ear.
Various Hz & dB
levels are presented.
• Determination of
bone conduction
“threshold.”
Bone Conduction Testing
Air Conduction & Bone Conduction
Hearing
Audiogram
• Results of audiometric
testing are displayed
on a graph (dB x Hz).
• Smallest numbers are
at the top of the graph
• Shaded areas
represent the general
range of normal
hearing
X = Left Ear
Normal range of human
hearing is 20 Hz to 20,000 Hz
O = Right Ear
Hearing Loss
X = Left Ear
O = Right Ear
Another Test of PAS: Otoacoustic
Emissions (OAE)
OAE Examples
Normal Emission
Impaired Emission
Testing the CAS
• Evoked
Responses
• Auditory
Evoked
Response
• Auditory
Brainstem
Response
(ABR)
ABR Examples
Testing the CAS: ABR
Types of Hearing Loss
Portion of Auditory System Affected:
Conductive Loss
Sensorineural Loss
Mixed Loss
Ear Affected:
Unilateral
Bilateral
An otoscope
Conductive Hearing Loss
Results from interference
of sound waves that
would normally pass
through the outer and
middle ear.
Can be completely
corrected (“reversed”) in
most cases.
Conductive Hearing Loss: Outer
Ear Atresia
Conductive Hearing Loss:
Perforated Ear Drum
Conductive Hearing Loss:
Impacted Cerumen
Conductive Hearing Loss: Otitis
Media
Myringotomy & Grommets
Sensorineural Hearing Loss
Results from damage
to the cochlea or the
auditory nerve and
upwards (CAS). The
electrical transmission
of the sound is
affected.
Can generally not be
fully corrected
(irreversible).
Sensorineural Hearing Loss:
Tumour
Sensorineural Hearing Loss: Noise
Induced
Sensorineural Hearing Loss:
Presbycusis
Sensorineural Hearing Problem:
Tinnitus
Mixed Hearing Loss
Results from
interference of
sound waves
through outer
and/or middle ear
AND the electrical
transmission of the
sound.
Hearing Loss: Demographics
• 10.5% of NZ population experience hearing loss (approx
450,000 people)
• NZ European 10%
• Maori 12%
• 2 per 1000 newborns (well-baby)
• 4 per 100 newborns (NICU)
• 4% of population below 45-years of age
• 30% of population over 65-years of age
• 36% of population over 70-years of age
Levels of Hearing Loss
Deafness
Defined: The permanent and profound loss of
hearing in both ears with an auditory threshold of
more than 90 decibels.
Hard of Hearing: Mild to Severe loss of hearing.
Types of Deafness
Congenital & Adventitious
Language & Deafness
Prelingual & Postlingual
Risk Factors for Hearing Loss
• Early Age Factors:
– Genetically inherited (50% of all
hearing impairments “run” in families)
– Prenatal Disease (rubella, meningitis)
– Prematurity (less than 37 weeks
gestation, LBW<1500 grams)
– Chronic Otitis Media
Risk Factors for Hearing Loss
• Later Age Factors:
– Noise (cochlear damage)
– Ageing (Presbycusis)
– Drugs (asprin, Lasix)
Management of Hearing Loss:
Amplification
• Typically any hearing loss greater than 25dB
is considered (uni- or bi-lateral)
Hearing Aid Components
• Microphone
• Amplifier
• Speaker
Types of Hearing Aids
Body Aid
Management of Hearing Loss: Implants
•
•
•
•
Bone-anchored Hearing Aid
Cochlear Implant
Brainstem Implant
Middle Ear Implant
• Involves bypassing or
artificially stimulating
structures of the auditory
system that are not
working properly.
Bone-Anchored Hearing Aid (BAHA)
A BAHA is an auditory implant
for people with hearing loss
who don't benefit from normal
(air conduction) hearing aids.
Most common reasons for
BAHA are:
– Chronic OM - when wearing normal
hearing aids makes the infection
worse
– single sided deafness due to tumours,
surgery or trauma
– children born with abnormal ears
Cochlear Implant
• Typically reserved for individuals with severe to profound
hearing loss by stimulating the auditory nerve. The implant
does not restore normal hearing.
Cochlear Implant
Middle Ear Implant
• External receiver delivers
sounds to a transducer
implanted in the middle
ear that causes the
ossicles to vibrate.
• Ideal for individuals who
cannot tolerate a
traditional type of hearing
aid that is inserted to the
ear canal.
Auditory Brainstem Implant
The first device
specifically designed
to bypass the cochlea
and the auditory
nerve to transmit
sound directly to the
brainstem.