Transcript The Basic Audiologic Evaluation

The Basic Audiologic Evaluation
An introduction to audiometry
and impedance testing
Nicole J. Lanthier, MA, CCC-A
Clinical Audiologist, Reg. CASLPO
What is an Audiologist?
• A professional holding a Master’s degree in
Audiology, as well as a professional license
or certification, who is educated in the areas
of hearing measurement, hearing disorders,
aural rehabilitation, amplification, &
hearing conservation
– Otolaryngologist ~= Opthalmologist
– Audiologist
~= Optometrist
– HearingAid Dispenser ~= Optician
Who Needs Audiologic Testing?
• Infants, children, and adults
• people known to be at risk through genetics,
noise exposure (ongoing or episodic), ototoxic drug exposure, aging, related health
issues or trauma, those who are concerned
about difficulties hearing (or friends/family
are concerned about their hearing)
• age = birth - 130 years
The Basic (Adult)
Audiologic Evaluation
•
•
•
•
•
history, reason for referral
otoscopy
tympanometry
stapedial reflexes
pure tone audiometry
– air and bone conduction; masking
• speech testing (speech audiometry)
Tympanometry
• tympanometry = an objective measure of
eardrum compliance change as air pressure
is varied in the external ear. An assessment
of eardrum mobility. Also called dynamic
compliance
• tympanometric curve = pressurecompliance function
The Tympanogram
• Measured on an “impedance bridge”
• A tympanogram will give an indication of
the status of the middle ear, in terms of
compliance
– is the middle ear system “stiff” or “floppy”
– what is the pressure in the middle ear space
– is the eardrum intact
Tympanometric Norms
for Compliance
• typically ~ 0.3 cc - 1.5 cc WNL for adults;
~ 0.2 - 1.0 cc for children
• lower than this indicates high impedance,
higher than this indicates high compliance
– low compliance may indicate middle ear
effusion or stiffening (otosclerosis)
– high compliance could indicate TM scarring
(flaccid monomeric areas), ossicular
discontinuity
Tympanometric Norms from Margolis &Heller, 1987
•
•
•
•
•
Compliance
(mmho or cc)
ADULTS
0.3 - 1.4
(X = 0.8)
Vol.
(cc)
Width
(daPa)
0.6 - 1.5
(X=1.1)
50 - 110
(X= 80)
• CHILDREN (age 3 - 5 years)
• 0.2 - 0.9
0.4 - 1.0
• (X = 0.5)
(X = 0.7)
60 - 150
(X= 100)
Liden-Jerger Classification
of Tympanometry
• categorical classification of tympanograms
• the most commonly used of classification
systems; uses “alphabet” category names
• normal tympanogram (normal
compliance, pressure, morphology) is
“Type A”
Type A with Subscript
• Type Adeep (Ad) denotes a tympanogram
with a peak and normal peak pressure, but
increased compliance
– e.g. peak pressure + 15 daPa, compliance 1.9cc
• Type Ashallow (or As) denotes a
tympanogram with a peak and normal peak
pressure, but reduced compliance
– e.g. peak pressure - 25 daPa, compliance 0.2cc
The Flat Tympanogram
• A flat or “type B” tympanogram can
indicate
– occlusive obstruction in the ear canal
• look for smaller EAC volume; otoscopy
– a TM which is not moving due to high middle
ear impedance
• look for normal EAC volume; otoscopy
– a perforated TM
• look for large volume; otoscopy
Type C Tympanogram
- Negative Pressure
• When peak pressure is lower than - 150
daPa this is a “Type C” tympanogram
• indicates negative middle ear pressure;
usually associated with eustacian tube
dysfunction
• compliance may be normal or reduced
– “type C” can be concomitant with, a precursor
to, or occur during resolution of middle ear
effusion
Stapedial Reflexes
(aka Acoustic Reflexes)
• Loud acoustic stimulus will cause bilateral
contraction (reflex) of stapedius muscles
• measured on an “impedance bridge”
• loud stimulus delivered to one ear, can
measure reflex response on the ipsilateral or
contralateral ear - measurement of both
“ipsi” and “contra” gives best info
Acoustic Reflex Pathways
• START: outer ear -> middle ear -> inner
ear -> VIII nerve -> cochlear nucleus ->
ipsilateral superior olivary complex
•
THEN
– IPSI - ipsi facial nerve - > ipsi middle ear
–
OR
– CONTRA - contra superior olivary complex ->
contra facial nerve -> contra middle ear
Stapedial Reflexes
(aka Acoustic Reflexes)
• use to detect non-organic hearing loss,
investigate facial nerve function, investigate
possible retrocochlear pathology
• reflex can be also be absent due to middle
ear dysfunction or severe hearing loss
• look at reflex threshold norms compared to
hearing levels
Reflex Decay
• reflex decay test - present stimulus tone 10
dB higher than the patient’s reflex threshold
for 10 seconds; 500 or 1000 Hz stimulus
• measure the amplitude of the reflex for 10
seconds, if it is reduced 50% or more in this
time period this is “reflex decay”
– suggestive of retrocochlear pathology
Pure Tone Audiometry
• Typically tested frequencies include 250 Hz
- 8000 Hz
• humans can hear ~ 20 Hz - 20 000 Hz but
this tested range of frequencies is the area
of our most sensitive hearing and the
frequencies most used in human speech
• may include ultra high frequency testing
(>8000 Hz) if monitoring high risk
individuals (noise, cisplatin exposure etc.)
Pure Tone Audiometry
• A calibrated audiometer is required to
ensure that the presented sounds are the
proper frequencies and intensities
• calibrated earphones required to deliver the
sounds
• quiet testing area required to ensure
detection of sounds is not masked
Earphones
• Earphones are sound transducers
• Common styles or earphones include
– supra-aural earphones
– circumaural earphones
– insert ear phones
• bone conduction transducer/headband
• speakers for sound-field presentation
Advantages of Insert Earphones
•
•
•
•
•
reduces chance of collapsing ear canals
best reduction of environmental noise
improved comfort
hygiene - usually disposable/cleanable tips
increased inter-aural attenuation
– less need for masking
– fewer masking dilemmas
Pure Tone Testing
• Typically used protocol is a bracketing
technique, beginning at 30 dBHL when
thresholds unknown, or ~10 dB above
known thresholds
• if no response at 30 dB, go to 50 dB
• bracket “10 down & 5 up”
– e.g. response at 30, go to 20, response at 20, go
to 10, no response at 10, go to 15; recheck 2-3x
Pure Tone Testing
• good idea to test better ear first
• if there is an asymmetry in hearing of over
60 dB when using insert phones, or 40 dB
using supra-aural phones, you may have
problems with crossover and inadvertently
stimulate the non-test ear
– inter-aural attenuation ~60 dB w/ insert
earphones, ~ 40 dB w/ supra-aural headphones
Crossover
• E.g. - thresholds of 10 dB left and
thresholds over 50 dB right will require
masking w/ supra-aural headphones
• e.g. thresholds of 10 dB left and thresholds
over 70 dB right will require masking with
insert earphones
• if you do not mask, the sound will cross
over via bone conduction
Crossover
• To prevent getting responses from the nontest ear in these situations you must use
masking noise
• for pure tone testing use narrow band noise
• for speech testing use speech weighted
noise
• remember crossover is by bone conduction
even if stimulating via air conduction
Masking
• Various equations used - example here
• For masking for air conduction
– threshold of non-test ear, plus 15 dB
– want to plateau 15 dB to ensure real threshold
– ideally want 30 dB effective masking
• remember that masking can also cross over, so you
don’t want to overmask and elevate threshold of
test ear- remember inter-aural attenuation
Masking Example - AC
• E.g. threshold left ear 10 dB, right 75 dB
• begin with masking left 25 dB, present tone
again right - if response obtained from right,
increase masking 5 dB, if no response,
increase presenting level to test ear by 5 dB
• follow this until you are able to increase
masking three times in non test ear with
reliable responses from test ear
Bone Conduction
• Bone conduction testing uses a vibrating
sound generator held to the head to
stimulate the inner ear ~ directly
• “bypasses” outer and middle ear systems
• usually test 250 or 500 - 4000 Hz with BC
• usually use pure tone stimuli
• typical placement on mastoid, (not touching
pinna) can use forehead, teeth, nose
Bone Conduction
• Use bone conduction when air conduction
thresholds are elevated & want to
differentiate b/w conductive and
sensorineural hearing loss
• conductive hearing loss - hearing loss due to
pathology of outer or middle ear systems
• AC thresholds elevated, BC thresholds
WNL = conductive hearing loss
Air-Bone Gap
• The difference b/w the AC and BC
thresholds is called the “air-bone gap”, or
the “conductive component”
• e.g. AC threshold 45 dB, BC threshold 5 dB
– air-bone gap, or “conductive component” 40dB
• this indicates normal function of the inner
ear and auditory CNS, problem OE or ME
Conductive Hearing Loss
• Conductive hearing loss associated with
–
–
–
–
–
–
otitis media
otitis externa
TM perforation
ossicular discontinuity
otosclerosis
occluded ear canal/stenosed ear canal
Sensorineural Hearing Loss
• if elevated AC and BC thresholds are the
same (or very close, 5 dB, together) then the
hearing loss is sensorineural
• e.g.AC threshold 45 dB, BC threshold 45dB
• OR
AC = 45 BC = 40
– no air-bone gap, bypassing the OE and ME
does not improve threshold, so hearing loss is
sensorineural - due to IE/possibly retrocochlear
Sensorineural hearing loss
• Called sensorineural since can be sensory or
neural: typically sensory, due to IE/cochlea
– popular but incorrect, “nerve deafness”
• Sensorineural hearing loss associated with
– noise exposure
– aging
– ototoxic drugs
-retrocochlear pathology
-illness (e.g.meningitis)
-labyrinthitis
Mixed Hearing Loss
• if there is an air-bone gap, but the BC
thresholds are not WNL, then it is a mixed
hearing loss
• the degree of hearing loss is partly due to
OE or ME and partly due to IE
• e.g AC threshold 75 dB, BC 40 dB
– air-bone gap 35 dB, BC threshold elevated out
of normal range (>25 dB)
Mixed Hearing Loss
• MHL has a component of CHL and SNHL
• Mixed hearing loss can be associated with:
– otosclerosis
– SNHL with otitis media,
• SNHL with cerumen occlusion
• SNHL with TM perforation
• SNHL with overlay of etc. etc. etc.
– post-surgical e.g. cholesteatoma removal
Speech Reception Threshold
• SRT - lowest dB HL at which (closed set)
speech can be understood
• usually obtained by presenting descending
levels of spondaic words (spondees) until
only 50% score is obtained
• use a list of 10-15 familiarized words
• spondee - two syllable word with equal
emphasis on both syllables (e.g. hotdog)
Speech Reception Threshold
• SRT is usually within ~ 6 dB of the pure
tone average (PTA = average threshold
using 500, 1000, and 2000 Hz)
• if hearing loss is steeply sloping or has a
“notch” SRT may be lower than PTA,
closer to “best threshold”
• quick reliability check - if SRT better than
thresholds would indicate - ? test validity
Speech Discrimination Testing
• Present a list of published phonetically
balanced words, usually 25 - 50 words at a
level allowing good audibility and comfort
• usually ~ 35 - 40 dB over PTA/SRT
• NU-6, W-22
• PBK for “kindergarten age” children
• modify for special needs (board, write etc.)
Hearing “Sensitivity”
vs. Hearing “Clarity”
• speech discrimination testing gives an idea
about the “clarity” of hearing
• patients with identical audiograms
(thresholds/sensitivity) may differ
significantly in their functional auditory
abilities depending on their speech
discrimination abilities
• unusually poor or asymmetric “discrim” can
suggest retrocochlear pathology
Infants/Toddlers
• Below age of 6 months use ABR and OAEs
• from age ~ 6 - 24 months use visual
reinforcement audiometry = VRA
• usually done “in the soundfield”, child
seated on parent’s lap between loudspeakers
in a soundbooth; reinforcing toys hidden
behind smoked glass on either side of child
• condition child to turn to sound & reinforce
Young Children
• Age ~ 2 1/2 - 5 years use play audiometry
• usually with earphones, condition child to
respond to perceived sounds with a “play”
response such as dropping a block in a
bucket or putting a sticker in a book
• can usually accomplish some speech testing
• children/adults with “younger functional
ages” can be tested in this manner as well
Amplification?
• people with hearing loss affecting the
frequency/intensity ranges of spoken
language will often benefit from
amplification (hearing aids or other varieties
of amplification)
• good speech discrimination allows better
amplified performance
• ensure appropriate hearing aid prescription
Other Audiologic Tests
•
•
•
•
•
ABR/BAER
ECOG
OAEs
CAP testing
tinnitus counselling
Re-Cap
•
•
•
•
otoscopy
tympanometry
stapedial reflexes
pure tone audiometry
– air and bone conduction; masking
• speech testing
• other tests as needed to follow up
Abbrevations Used
•
•
•
•
•
•
•
EAC = external ear canal
WNL = within normal limits
TM = tympanic membrane (eardrum)
SRT = speech reception threshold
PTA = pure tone average
OE = outer ear
ME = middle ear
Abbrevations Used
•
•
•
•
•
•
SNHL = sensorineural hearing loss
CHL = conductive hearing loss
MHL = mixed hearing loss
ABG = air bone gap
AC = air conduction
BC = bone conduction