Transcript Physiologic Measures

Physiologic Measures
Physiologic Tests in Audiology
Otoacoustic Emissions
Evoked Potentials
Immittance Measures
Alphabet Soup of Audiology
OAE, DPOAE, TEOAE, AABR, ABR, MLR,
T-grams, MNR, P300…
WHAT in the WORLD are those tests?


When would they be used?
What do they mean?
Otoacoustic Emissions
Just About Everything You Want
To Know About OAE
Origin
Types of Tests
Interpretation
Otoacoustic Emissions
First reported by Dr.
David Kemp in
England in 1978(2)
Two types of emissions
are routinely measured


Transient Evoked OAE
Distortion Product OAE
 Benefits of each type
are beyond today’s
lesson
FYI…Spontaneous
Emissions are
present in 60% of
normal ears, present
in females twice as
often as males(3)
Structures of the Inner Ear(1)
Cochlea - Snail-shaped
organ with a series of
fluid-filled tunnels
Rests deep in temporal
bone of skull
Footplate of stapes rests
in oval window of
cochlea
cochlea of guinea pig
Hair Cells of Cochlea
Frequency-specific


High frequency sounds,
basal end of cochlea
Low frequency sounds,
apex of cochlea
So What IS an OAE?
(4)
OAEs are actually soft sounds generated
by the movement of the structures (outer
hair cells) in the cochlea
Stimulation is sent in through the middle
ear, emission occurs within the cochlea,
sound then must travel BACK OUT
through the middle ear, external ear and
be recorded by the microphone of the
device
What IS an OAE?
• OAE will likely be
observed if auditory
threshold is between 0dB
and 30dB/40dB HL(5)
• Variables influence OAE




Middle ear state
Noise in room
Noise of subject
Debris in EAC
Response is
calculated above the
noise floor

1-2dB, up to 20dB
Measured across
frequency range
TEOAE
Transient Evoked Otoacoustic Emission
Abrupt Click or Tone Burst activates the
cochlea across a wide frequency region, if
outer hair cells are normal, TEOAEs are
produced(4)
TEOAE amplitude/noise floor difference
calculated at individual frequencies, usually
1K Hz to 5K Hz
Stimulation usually presented at 80dB SPL
Transient Evoked OAE
•The patient has an
auditory threshold of
50dB HL at 4KHz in
the left ear, otherwise
hearing is within
normal range
Distortion Product Otoacoustic
Emission - DPOAE (6)
Stimuli for DPOAE are
two closely spaced pure
tones, called f1 and
f2…the calculated
response is actually the
intermodulation
distortion product
produced by the ear
when stimulated
DPOAE
Usual frequency range for
stimulation is 500 to 10,000 Hz
Due to noise floor, difficult to
obtain results below 1500 Hz
Variable stimulation, generally
55dB SPL and 65dB SPL for f2
and f1, respectively
Tones across frequencies
presented
Distortion Product OAE
•Auditory
thresholds 0-5dB HL,
each ear; patient
is 41 year old female
DPOAE with Hearing Loss
52 yr male; Audio results
Left
Right
2K: 15
2K: 30
3K: 35
3K: 80
4K: 35
4K: 85
6K: 40
6K: 60
8K: 15
8K: 60
Use for Otoacoustic Emissions
Sensitive measure of outer hair cell function
Important for early identification and
diagnosis of auditory dysfunction in pediatric
and adult populations
Useful for screenings in newborn nurseries
Can confirm soundfield results in toddlers
Can substantiate results that are
“questionable” in adult patients who attempt
to feign a hearing loss
How to Interpret OAE?
NOT A TEST OF HEARING…RATHER,
A TEST OF OUTER HAIR CELL
INTEGRITY
Results provided by frequency ranges,
found to correlate with hearing in
normal range
Report summary will state at which
frequencies the responses were
obtained
Auditory Evoked Potentials
Terms, Definitions and Reasons to
Request AEP Tests
Interpretation of AEP Tests
Auditory Evoked Potential Tests
ABR, ECochG, AMLR, ALR, P300, MNR, 40Hz
Tests are far field recordings of
neurophysiological responses to auditory
stimulation…in a bioelectric background!(4)
Alteration of time windows, filters, and/or
stimuli will change the response…for some
tests, special equipment is necessary
Auditory Brainstem Response
(ABR) Tests
The most well known, the ABR,
discovered in 1971(7)

Primarily used to evaluate neurological
disorders at level of auditory nerve and
brainstem
ABR not significantly affected by most
drugs or subject state of arousal
Auditory Evoked Potential Tests
ABR allows tracking of electrical energy
via the auditory neural pathway to level
of inferior colliculus(8)
Presence of Wave V found to be reliable
estimate of hearing ability in 2K-4K Hz
range(8)
Results tracked to within 10-15dB of threshold
Latency/Intensity functions can indicate conductive loss, high
frequency loss, severe to profound loss…BUT, will miss low
frequency loss(6)
Auditory Evoked Potentials
Can be used as auto screen
method, AABR for Pass/Refer
Patient must be quiet, relaxed;
infants asleep or sedated
Click stimuli provides
information about 2K to 4K Hz
region of cochlea
Can use bone oscillator to
perform bone conducted ABR
Auditory Evoked Potentials
Possible to construct an “audiogram”
based on ABR results obtained with
500Hz, 1000 Hz, 2000 Hz tone bursts
Used to identify auditory dys-synchrony
(auditory neuropathy), a dysfunction of
neural pathways(9,10)
Auditory Evoked Potentials
Likely abnormal in
Patients with Multiple Sclerosis
and other demyelinating processes
 Hyperbilirubinemia at levels requiring exchange
transfusion
 Patients with severe high frequency loss

ABRs, like OAE, NOT a test of hearing,
but of neural function, neural
synchrony
Auditory Evoked Potential Test
Subject variables that affect results(8)

Age
 Gestational age at least 27 weeks to observe ABR
 Latency, amplitude change in expected fashion
until 18-24 months, when ABR becomes adult-like
 Extensive normative data available by age range


Gender
Muscular artifact
Other AEP Tests
AMLR Auditory Middle Latency Response
ALR Auditory Late Response
P300 Event Related Response
40Hz Variation of MLR
On-going studies regarding clinical utility of
these tests continue
Most recorded since 1960s(6)
Not in widespread use outside of research sites
Why Request an Evoked Potential
Test?
Can be used to construct an audiogram in
patients incapable of voluntary responses
(infant, mentally handicapped)
In adults, rule out retrocochlear or
demyelinating process
More Reasons to Request AEP
To construct an audiogram in noncooperative adults (malingering)
To identify auditory dys-synchrony
(auditory neuropathy) (10)
To assess aided thresholds
when behavioral testing
not possible (13)
Auditory Evoked Potential Tests
Not necessarily first line of testing for
Audiologists!!
When referring children/infants for
auditory evaluation, evoked potential
tests may be the last needed, following
soundfield, OAE, BOA, VRA, etc.
Sedated ABRs can often be avoided,
use other methods first
Immittance Measures
Tympanogram
Acoustic Stapedial Reflex
External Auditory Canal
Approximately 2.5 cm
in length
“S” shaped
Lined with cerumen
and sebaceous glands
Outer 1/3 cartilage;
inner 2/3 temporal
bone(1)
What IS Immittance?
(6)
Combination of two words


Admittance is the reciprocal of Impedance
Acoustic admittance is a measure of the
flow of energy through middle ear and
impedance is the opposition to this flow
No better, quicker or less expensive
single audiologic procedure exists to
assess status of middle ear, cochlea,
eighth nerve and lower brainstem than
a complete Immittance Battery
Tympanic Membrane(1)
Thin membrane, made
of three layers
Forms boundary
between outer and
middle ear
Vibrates in response to
sound
Changes acoustical
energy into mechanical
energy
The Ossicular Chain(1)
A Malleus
B Incus
C Stapes



Ossicles are smallest
bones in the body,
fully formed at birth
Act as a lever system
Footplate of stapes
enters oval window
of the cochlea
Eustachian Tube(1)
Lined with mucous
membrane; connects
middle ear to back of the
throat (nasopharynx)
Equalizes air pressure
Normally closed except
during yawning or
swallowing
Not a part of the hearing
process, but status can
influence hearing ability
Stapedial Muscle
(11)
Connects the stapes to wall of middle ear
Contracts in response to loud sounds;
known as the “Acoustic Reflex”
Can be stimulated ipsilaterally or
contralaterally
Valuable Information/Simple Test
Test results reveal



Ear canal volume(6)
Children 0.42ml to 0.97ml
Adults 0.63ml to 1.46ml
Peak amplitude of tympanogram
Pressure point of peak
Normal values +/- 100mm H2O
Tympanogram Types
Modified
Jerger
Classification
System(6)
A(d)
A
A(s)
B
C
Some Thoughts in Closing…
•Physiologic test measures in Audiology
may be used on patients of any age and
provide valuable information about
auditory-neural functions
•While these tests are NOT direct tests
of hearing, information about the
auditory system is provided
•Otoacoustic Emissions
•Auditory Evoked Potentials
•Immittance Measures