Download OAEs

Advanced Issues in
Otoacoustic
Emissions
Thierry Morlet, Ph.D.
Outline
 Cochlear Physiology
 OAE definition, Types and Characteristics
 Interpretation of OAEs
 OAE measurements
 OAEs variation in Clinical Populations
 Clinical Applications of OAEs
Organ of Corti
12,000 Outer Hair Cells
Scala Vestibuli
4,000 Inner Hair Cells
Scala Tympani
Hair Cells
Tallest stereocilia are embedded into
The tectorial membrane
The IHC stereocilia can be
considered freestanding
in the subtectorial space
Innervation
20 cochlear
afferents
nerve
endings per
IHC
L. Andrade and B. Kachar, NIDCD/NIH
Afferent Innervation
 The vast majority of the afferent
auditory nerve fibers form one-to-one
connections with a single IHC after
entering the cochlea
 A minority (about 5%) of the afferent
neurons cross the organ of Corti and
connect with groups of OHC
 The afferent innervation of OHC and
IHC has little, if any, impact on OAEs
Efferent Innervation: The olivocochlear
System
Cochlear Potentials
 Endocochlear potential
 Cochlear microphonic
 Summating potential
 Compound action potential
 Otoacoustic emissions
OHC Electromotility
 There is a constant drive of potassium
from the endolymph into the OHC.
 When stimulated, the stereocila will bend
which opens more ion channels into the
OHC and lead to their depolarization.
 The depolarization is the trigger for the
activation of electromotility.
 Hyperpolarization causes OHC elongation
 Depolarization causes OHC contraction
Cochlear Active Mechanism
Dr Ashmore, 1987
Amplification/Fine Frequency Discrimination
Otoacoustic Emissions
 First discovery by Kemp (1978)
 Discovery of motile characteristics of OHCs:
Brownell et al., 1985
 The origin of OAEs is ascribed to processes
associated with the mechanical motion of the
OHCs, and OAEs are thought to be modulated
by the efferent auditory pathways via the
olivocochlear system.
 OAEs appear sensitive to subtle changes in
cochlear function that are not revealed in the
octave interval behavioral audiogram.
 OAEs have high test-retest reliability, which
contributes to their clinical utility.
The OAE Story (by Dr Kemp)
 Nobel Prize winner George von Bekesy first explained
how sound created travelling waves on the basilar
membrane in the 1940s.
 The travelling wave separated frequency components in
the cochlea but the degree of frequency separation seen
by Bekesy in human ears post mortem was quite poor.
 In contrast, recordings made in auditory nerve fibers
themselves showed that the healthy cochlea somehow
managed to achieve sharp frequency division.
 As early as 1948, Thomas Gold argued that to achieve
simultaneously both high sensitivity and high frequency
selectivity there must be a biological vibration amplifier.
As in primitive radio receivers, this extra energy could be
applied as positive feedback to the travelling wave to
overcome the natural viscous loss of energy.
 Gold explained his ideas to von Bekesy but neither he nor
any other auditory researcher took Gold’s ideas seriously.
The OAE Story

“In July of 1977 the crucial experiment was performed. I placed a
miniature microphone salvaged from a hearing aid over the
opening of my ear canal and then closed the ear canal with silicone
putty to keep the ear’s sound in. I fed the output of the microphone
into a hetrodyne analyser - an instrument which allows you to tune
in to a very narrow frequency band (10Hz) at any frequency. Via a
headphone I then applied a single pure tone at a frequency and
level that I knew would give rise to a clear aural distortion tone as
the external tone combined with the (supposedly) internal
oscillation. I knew the frequency of the combination tone exactly by
applying the formulate 2f1-f2 to the external tone (f1) and the
internal tone (f2) and I accurately tuned the analyser to this
frequency. Immediately there was a reading on the dial!

As I changed the frequency of the external tone, the frequency of
the combination tone in the ear canal changed exactly as the
formula predicted. The internal tone was therefore physically
present - not a neural phantom - and so should it also be detectable.
I turned off the stimulus tone and tuned the analyser to the
frequency of the supposed internal tone. It was there. A signal of
85dBSPL at 1253Hz was continuously present in my left ear canal.
And another at 1760Hz. What’s more, they were still there the next
day at exactly the same frequency - within 1 or 2Hz. Such stability
was difficult to obtain even with high quality electronic equipment
in those days - and to find it in a biological system was hard to
believe. But the evidence was incontrovertible.”
The OAE Story
 “In 1977, it seemed that, as in 1948, the true
significance of these experiments for auditory
science might be lost due to entrenched thinking
and misunderstandings about the highly technical
acoustic experiments. To help overcome this, one
final experiment was performed. The reasoning was
that if sound energy reverberated inside the cochlea
as it did in a large room, then applying a short click
to the ear would, like a clap in a room, resulting an
echo. The hetrodyne analyser was replaced by a
physiological signal averager and the pure tone
stimulus was replaced with a click. Sure enough, the
ear gave an evoked response to the click – a long
complex emission of sound lasting 16 milliseconds
and more. It was like nothing seen before from the
auditory system. It was a cochlea echo.”
The OAE Story
 The first scientific presentation of acoustic
emissions was in April 1978 at a meeting of
the British Society of Audiology in Keele
University. The new discovery was
received with great skepticism, not least
because the concept of waves travelling in
reverse in the cochlea contradicted firmly
held views at the time.
 Many physiologists also doubted the early
evidence that OAEs came from the
cochlea.
Types of OAEs
 After their discovery, the otoacoustic
emissions (OAEs) were classified on the
basis of the nature of the stimuli used to
evoke them.
 2 main categories:
– Spontaneous otoacoustic emissions (SOAEs) are
recorded in the absence of external stimuli.
– Evoked OAEs: OAEs recorded with stimuli.
Classification of OAEs
 Among the OAEs generated by a stimulus, we distinguish 3
categories:
– Distortion product otoacoustic emissions (DPOAEs): OAEs evoked using
tonal pairs. They appear at frequencies consistent with intermodulation
distortion of the 2 stimulus tones.
– Transient (or click-evoked) otoacoustic emissions (TEOAEs, CEOAEs): OAEs
generated with a very brief stimulus (click).
 A subcategory is the toneburst OAEs (TBOAEs): OAEs generated by a
very brief sound that contains less frequencies than a click (tone-burst).
These TBOAEs are mostly used in research and have less of a clinical
application.
– Stimulus frequency otoacoustic emissions (SFOAEs): evoked by a single
tonal stimulus. The frequency of the SFOAE is identical to that of the
stimulus.
Spontaneous Otoacoustic Emissions (SOAEs)
 Occur without external stimuli
Transient Otoacoustic Emissions (TEOAEs)
 Elicited by brief pulses (clicks or tonebursts or
even amplitude modulated tones, etc.).
Distortion Product Otoacoustic Emissions
(DPOAEs)
 Recorded in response to pairs of tones
Classification of OAEs
 The classification of OAEs based on the
sound (or absence of sound) used to
generate them is still in use today.
 Another way of classifying the OAEs has
emerged more recently.
 OAEs can be classified based on their
mechanisms of generation (according to
Kemp and his colleagues):
– Wave-fixed OAEs: when their generators
move or translate along with the envelope of
the travelling waves of the stimuli.
– Place-fixed OAEs: when their generators are
fixed in place along the basilar membrane.
Classification of OAEs
 A more formal model has been developed by
Shera and Guinan (1999). In this model, OAEs are
generated by 2 mechanisms:
– Reflection (roughly similar to place-fixed OAEs)
– Distortion (roughly similar to wave-fixed OAEs)
 OAEs recorded in the ear canal could also be due
to the 2 different mechanisms (mixed OAEs) when
contributions of each mechanism are present.
Transient Evoked OAEs
TEOAEs
 Equivalent to click-evoked OAEs (or CEOAEs)
 Recorded with clicks of very short duration
(80 microseconds).
 Depending on the intensity of the click, 2
different protocols are available:
– Non linear
– Linear
 The first few milliseconds of the post-stimulus
window are discarded before transforming
the data to the frequency domain.
 The level of the TEOAEs in comparison to the
noise floor is analyzed by frequency bands.
Absent TEOAEs
TEOAEs
Linear Recording from a preterm neonate
Quickscreen recording from a preterm neonate
TEOAEs elicited by Tone Bursts
2 kHz
4 kHz
Characteristics of TEOAEs
 The prevalence of TEOAEs is close to 100% in normally
hearing adults.
 Highest amplitude from 1000-2000 Hz in adults; more higher
frequency components in infants.
 Noise tends to be concentrated in the lower frequencies
 Show a unique “signature” in individuals, based on
characteristics of ear.
 Higher amplitude in females than in males.
 Higher amplitude in many individuals in right than left ears.
 Amplitude decreases with age. Neonatal subjects have
significantly stronger emissions than adults and under
normal conditions a lower average of stimuli is sufficient to
obtain a good response.
Age and Otoacoustic Emissions
• Highest amplitude in infants and
children than in adults.
• More high frequency components in
infants. Higher response from 10002000 Hz in adults.
• Criteria to interpret
absence/presence of OAEs
essentially similar in newborns,
infants, children and adults (i.e.,
signal to noise ratio).
• However, the normative data used to
decide if OAE amplitude at specific
frequencies is normal or abnormal
are different.
TEOAEs and Hearing
 TEOAEs are usually not present when the average pure tone
threshold is higher than 35 to 40 dB HL.
 TEOAEs cannot predict the auditory threshold. The reason is
the fact that auditory perception involves other parts of the
auditory system than just cochlear mechanisms.
 Nevertheless when:
– The external and middle ear functions are
normal.
– There are no inner hair cells and/or
retrocochlear hearing complications
The audiometric outcomes and the information
from the TEOAEs are in agreement.
Distortion Product OAEs

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The DPOAEs are recorded by stimulating the cochlea simultaenously
with 2 pure tones.
The cochlea generates additional tonal signals at frequencies
arithmetically related to those of the stimulus tones.
The pure tones which stimulate the cochlea are called primaries and
they are assigned as F1 and F2 and their corresponding amplitudes
are assigned as L1 and L2.
The most prominent and mostly used in clinical practice is the cubic
difference distortion product denoted as 2F1 - F2.
The healthy cochlea generates other DPOAEs: 3f1-2f2, 2f2-f1, 3f2-2f1,
etc.
The primaries should have frequencies which are close to one
another. The ratio of the F2 / F1 frequencies is called frequency ratio.
The choice of the frequency ratio has an effect on the amplitude of
the DPOAEs at different tested frequencies. Most prominent DPOAE
for FR between 1.20 and 1.22.
DPOAEs
 Two main types of DPOAE protocols:
– Primaries with equal intensities (L1 = L2), for example 70-70
dB SPL.
– Unequal primary intensities (L1 > L2), for example 65-55 dB
SPL. The latter can identify better cases with hearing
impairment and they are used in most screening programs.
 When asymmetrical DPOAE protocols are used, the
intermodulation components are generated close to
the F2 primary tone. Therefore the DPOAE information
is referenced to F2. When symmetrical protocols are
used the DPOAE information is referenced to the
geometric mean, which is defined a the square root of
F1 * F2.
DPOAEs
 There are two ways to present the DPOAE
information:
– In the DP-gram modality we measure the 2F1 - F2 amplitudes
at various F2 frequencies, having fixed the stimulus
intensities, for example F1=65 dB and F2=55 dB SPL.
– In the Input -Output (IO) modality, we measure the 2F1 - F2
at a fixed F2 frequency, varying the primary stimulus levels.
 For screening applications a small number of
frequencies is tested, such as 2.0, 3.0 and 4.0 kHz
(referenced to F2). For ototoxicity- monitoring
applications the bandwidth of the measurements
extends up to 8-10 kHz (referenced to F2).
DPOAEs
DPOAEs
DP-gram: measure the 2F1 - F2 amplitudes at various F2 frequencies,
having fixed the stimulus intensities, for example F1=65 dB and F2=55
dB SPL.
Input/Output Function
Input -Output (IO)
modality:
measure 2F1 - F2 at a
fixed F2 frequency,
varying the primary
stimulus levels.
DPOAE Microstructure
Number of points per octave depends on time available and desired frequency
resolution.
DPOAE Characteristics
 The prevalence of DPOAEs is close to 100% in normal adult ears.
 Highest amplitude at 1000-2000 Hz.
 Responses from the left and right ears are often correlated
(that is, they are very similar).
 For normal subjects women have higher amplitude DPOAEs.
 Aging process has an effect on DPOAE responses by lowering
the DPOAE amplitude and narrowing the DPOAE response
spectrum ( i.e. responses at higher frequencies are gradually
diminishing).
 DPOAE amplitude is dependent on frequency relationship
between the two tones.
 DPOAE amplitude is dependent on intensity relationship
between the two tones.
DPOAE Characteristics
 The relationship between DPOAEs and Audiometric
outcomes (mainly with the Pure Tone Audiometry) has
been also a debating issue from the early days of
otoacoustic emissions. While it is known that hearing
impairments higher than 30 to 40 dB HL cause a
significance decrease of the TEOAE responses, the same it
is not valid for DPOAE recordings. Due to the efficiency of
the DPOAE stimulation schemes it is possible to record
responses even from cases presenting hearing losses as
high as 50 dB HL.
When:
– The external and middle ear functions are normal.
– There are no retrocochlear hearing complications
The audiometric outcomes and the information from the DPOAEs
are in agreement.
Spontaneous OAE
 SOAEs are low level tonal
signals that can be recorded in
the external auditory meatus in
the absence of any stimulus.
 SOAE are recorded using the
same equipment as other types
of OAEs. The same sensitive
microphone is required.
 SOAEs can be recorded at any
time, even during sleep
(babies).
SOAEs
SOAE Characteristics
SOAE Number
8
6
4
2
0
The prevalence of SOAEs
has been shown to be higher
in newborns and infants
than in adults.

Newborns
Adults
SOAE Frequency
Higher frequency in
newborns and infants than
in adults.

0.5
2.5
4.5
Gender Prevalence
The
SOAEs demonstrate a
gender-prevalence, in that
they are significantly more
prevalent in women than
men and with higher
numbers of SOAEs in
females than in males.
Right Ear Advantage
There
is a higher
prevalence of SOAEs and a
greater SOAE number in
the right ear than in the
left ear.
 SOAE presence is
suggested to be linked to
higher auditory sensitivity.
Vincent van Gogh.
Self-Portrait with Bandaged Ear
1889; Oil on canvas; Courtauld Institute
Galleries, London
TEOAEs and SOAEs
 SOAEs are an indicator of strong and robust TEOAEs.
SOAE Characteristics
 The prevalence of SOAEs was first estimated at less than
40%.
 The prevalence is now estimated at approximately 80%,
with more SOAEs recorded in newborns and infants than
in adults.
 The increase in prevalence is mostly due to the
improvement in instrumentation leading to lower noise
floors. Low level SOAEs can now be unrevealed.
 In a laboratory setting, it is now expected to record
SOAEs in almost all normal-hearing young adults.
 SOAEs are very stable with time and do not fluctuate
much in frequency, making them a good indicator of
trauma that can occur in one ear, as with other types of
OAEs. However, the amplitude of each SOAE can
fluctuate by as much as 10 dB depending on the time of
recording.
SOAE Characteristics
 SOAEs are though to reflect the activity of the cochlear
amplifier.
 Absence of SOAEs does not signify that the subject has a
hearing loss.
 However any insult to the cochlear amplification process
will adversely affect the SOAEs.
 In fact, there seems to be a significant correlation between
the global presence of SOAEs and good hearing sensitivity.
 There is no known correlation between SOAE number and
audiological assessment.
 Many studies suggest that SOAEs are markers of cochlear
damage.
 The functional relevance of the presence of SOAEs is far
from clear.
Two Different Types of SOAEs?
 To reconcile the presence of SOAEs in subjects with
high auditory sensitivity and SOAEs due to cochlear
damage (noise for example), some hypothesized
that they may represent 2 distinct classes of SOAEs.
– SOAEs recorded in normal-hearing individuals are the
result of the active cochlear mechanisms and a
phenomenon of global resonance in the cochlea.
– Isolated, high-level SOAEs associated with cochlear
damage could be a result of artificial punctate
boundaries produced along the cochlear partition,
which act as barriers or reflectors creating SOAEs.
 Because SOAEs are not present in 100% of normalhearing adults, their clinical use remains uncertain
at the present time.
 SOAEs are commonly not recorded in clinical
settings, except in specific situations (tinnitus, etc.).
Interpretation of OAEs
Interpretation of OAEs
 Stimulus stability: 80 or 90% or greater
 Overall amplitude: Above noise
– S/N of 3 to 6 dB used
– Absolute amplitude varies widely
 TEOAE reproducibility
– Overall or by frequency bands
– Adults: 80% or greater
– Infants: 50-60% or greater acceptable
 Main criteria: Presence or absence of OAEs.
 OAEs can be absent with functioning Outer Hair
Cells.
 No correlation between OAE amplitude and ability
to hear.
Interpretation of OAEs




Main criteria: Presence or absence of OAEs.
OAEs can be absent with functioning Outer Hair Cells.
No correlation between OAE amplitude and ability to
hear.
Misconception: DPOAEs are more frequency sensitive
than TEOAEs. This misconception has been generated by
the familiar audiological representation of the DPgram.
In reality, both types of OAEs provide frequency specific
information for a particular cochlear segment.
PASS
FAIL
?
?
Pass?
Interpretation of OAEs:
what are YOUR criteria?
Diagnostic OAEs
 Obtain a high degree of frequency specificity on
the function of the Outer Hair Cells.
 For DPOAEs: at least 5-8 frequencies per octave
over the range of 500 to 8000 Hz.
 TEOAEs: are usually covering all available
frequency bands from 0 to 5000 Hz.
 The test will define:
– Normal amplitude (within a frequency region)
– Present OAEs but with abnormal amplitudes
– OAEs not present
Diagnostic OAEs
 Verify that the recording parameters were
adequate:
– Stimulus intensity closed to the target level
– Noise within the normal range
– OAEs above the noise floor (6 dB) for all
frequencies or only some frequencies?
– TEOAE reproducibility above 90%
– OAE amplitude within normal limits (if not,
OAEs could be absent or present but abnormal)
OAE Measurement

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Status of the external and middle ears
Fitting of the probe
Stimulus characteristics and stability
Noise
– Physiologic
– Environment
 It is easy to misinterpret OAE results if these factors
are not controlled properly.
 Identify the presence of a response.
 Determine whether criteria for an acceptable
response have been met.
 Interpret the amplitude and frequency
characteristics of the response.
Screening/Diagnostic Equipment
 Screening:
– Usually only display a “pass/refer” outcome.
 Diagnostic:
– Display the stimulus, OAEs and noise levels
– Number of artifacts
– Artifact rejection limit
 Other significant differences:
– TEOAE and DPOAE frequency and intensity
ranges usually much smaller for a screening
than a diagnostic system.
– Results may not be stored with a screening
system.
OAE Probe
 Size and shape do matter:
– will it be easy to fit the probe in a variety
of ear canals?
– Will the probe be comfortable for the
patient?
 Choose an OAE probe with a design to
safeguard against easy entry of
cerumen or debris.
 Choose an OAE probe that is easy to
clean.
Calibration
 Standards for calibration of OAE equipment are
not well established.
 It is important to understand the calibration
method used with the equipment in obtaining
norms.
 Normative data may be built-in the system. How
were they obtain?
 When starting using a new piece of equipment,
obtaining your own norms on a subset of patients
in your specific environment would be ideal.
Calibration
 Proper calibration is important to ensure that the
desired stimulus is being presented to the
patient’s ear.
 Proper calibration also ensures that the recorded
signal is a reasonable approximation of the
physical signal that was present in the ear canal.
 Proper (and consistent) calibration allows us to
compare a patient’s result over time with
confidence.
 Proper calibration also allow us to compare a
patient’s result with those published.
Recording Considerations
 Equipment:
–
–
–
–
Calibration of the probe.
Try the probe every day.
Clean the probe.
Visual inspection before and after every
procedure is important.
– Check noise level during recording.
Probe Fitting
 Probe fit is assessed with an analysis of
the response to a broadband signal
presented in the ear canal.
 Specific features will detect a leak in
the fitting of the probe, a blocked
probe or other anomalous conditions.
 Usually the equipment doesn’t allow
the recording to proceed if the fitting is
not appropriate (check your manual).
Probe Fitting
 The cable of the probe should be directed 45°
towards the top of the head. Experience has
shown that this angle is not feasible with
neonatal subjects, where a wider angle is
used.
 The position of the probe into the external
auditory canal is a crucial component of the
proper conduction of the test especially in
newborns.
 Deeper insertion of the probe tip within the
ear canal and tighter probe tip coupling
within the ear canal will decrease the ambient
noise.
 Experience is key!
Probe fitting
A standard click stimulus is applied
and the sound in the ear canal is
displayed as a waveform and
spectrum so that the operator can
adjust the fit of the probe and
ensure proper stimulation for
performing correctly the
test.
Probe Fit
 Although the probe is unlikely to move in older
children and adults during the recording as long
as the probe was well fit at first and the patient is
still, it is a likely scenario in young infants.
 Visual inspection of the probe and of the stimulus
and noise values should be done periodically
during the recording.
 Clinical devices usually give an indication if the
stimulus characteristics or the noise level are
changing during the recording.
Recording Considerations
 Environment:
– Depends on the age of the subject (sound treated booth, quiet
room, noisy nursery….).
– Will define the setting of the recording: noise level considered as
adequate in a booth setting will not be in a nursery.
– OAE amplitude is higher in newborns than in adults; therefore, a
higher level of noise will still allow OAE recordings in neonates –
except for low frequencies.
– Night Time?
 Subject:
– Relaxed, comfortable
– OAE can be recorded from sleeping or sedated children.
Noise
 High noise level in the ear canal affects the OAE
recording and can obscure partially or totally the
response.
 Low frequency noise (below 1-1.5 kHz) is
inevitable, because it is linked to body functions.
 By looking at normative data, it is possible to have
an idea of an “acceptable” noise level.
 Noise levels will however vary considerably
depending of factors linked to the equipment, the
patient population and the test setting.
Minimizing Noise Level
 Turn off equipment not in use in the test setting.
 Ask colleagues and family members that the recording will
start and to stay quiet.
 Ensure quiet environment outside the testing room.
 Adequate probe and tip size.
 Tight coupling between the tip and the ear canal with probe
deeply inserted.
 Position the tested ear away from running equipment
(computer fan, general ventilation, etc.)
 Replicate OAE recordings for some frequencies if they are
obscured by noise if possible.
 If patient is old enough, instruct to remain still and quiet (no
chewing).
 For younger infants, maintain their attention in one direction
to avoid motion.
 Always monitor the noise level during the recording: if it
changes suddenly, something is going wrong!
Stop criteria

The stop-criteria for the test vary.
 Can be set up for a specific protocol / clinical
population.
 The majority of programs use a pre-specified
number of sweeps for each subject category
(neonates, NICU residents, children, young
adults, adults).

Can be adjusted manually in some circumstances if
needed.
Stop Criteria
 It is also common to stop the recording when a variable
reaches a specific value.
 Several factors to take into account:
–
–
–
–
OAE amplitude level
Noise floor level
Signal-to-noise ratio
Maximum recording time
 Examples
– when the overall TEOAE reproducibility exceeds 75%.
– when the S/N ratio at certain frequencies is above a pre-determined
level (6 dB).
– when the DPOAE level reaches a predetermined level (10 dB SPL).
– when the noise floor reaches a predetermined level (-20 dB SPL).
 General rule: reduce the testing time to a minimum (define
optimal recording conditions).
 With a screening equipment, the outcome are preset. However,
several changes can be made if needed (know your screening
machine).
Artifact Rejection
 OAEs in the ear canal are easily contaminated by
ambient and physiologic noise.
 Clinical equipment incorporates built-in functions
to recognize and reject artifacts.
– The ambient noise that is not with the frequency range of
interest can be eliminated by filtering.
– Very large level signals can be rejected automatically. This
option is usually controllable. The threshold for rejection
will vary depending on the environment (NICU, sound
proof room) and the patient (quiet child, moving infant).
Ideally, the rejection limit will be set up to avoid including
too much noise while minimizing the duration of the test.
Outer Ear
 Plays a crucial role in the stimulus delivery and
otoacoustic emission recording
 Any debris or excess of cerumen will influence
the OAE recording
 The ear canal acoustics influence the stimuli used
to generate the OAEs.
 Importance of calibration (clinical systems do it
automatically)
 A variety of pathologic and nonpathologic
conditions of the external ear can affect the OAE
recording
Influence of External Ear Conditions
 Visual inspection is important when possible.
 Removal of any debris, foreign objects,
excessive cerumen, etc. will not only change
the OAE results but also improve the patient’s
comfort.
 Cerumen or debris
– Occlusion of stimulus and/or microphone ports in
the OAE probe.
– Blockage of stimulus energy delivery or return
from the probe to the tympanic membrane.
 Otoscopic inspection is not necessary if
patient was just seen for an otologic
inspection and in most newborns (unlikely to
have pathology, foreign objects or cerumen).
Middle Ear
 Both the stimuli and the OAE have to travel into
and from the cochlea through the middle ear
 The middle ear condition is thus very important in
OAE recording
 Middle ear dysfunction will lead to either OAE
reduced in amplitude or OAE not detectable at all
in the external ear canal
 Middle ear dysfunction SHOULD be ruled out
before concluding that OAE abnormalities are
secondary to cochlear dysfunction
Influence of Outer Ear and Middle Ear
Conditions
 TM perforation
 Eustachian tube dysfunction
 Negative or positive pressure
 Middle-ear effusion
 Ventilation Tubes.
– OAEs can be recorded in presence of tubes, but not in
100% of ears.
 Always eliminate the possibility of external or
middle ear problems when interpreting abnormal
OAE results.
Influence of Middle Ear Function
 When OAEs are abnormal (partially or totally in
terms of frequency), the middle ear function must
be evaluated.
 The status of the Outer Hair Cells can only be
inferred if the middle ear status is known and
middle ear pathology ruled out.
 Inversely, normal OAE findings (normal amplitude
for the entire frequency range) argue strongly for
normal middle ear function (no need for middle
ear evaluation, notably in newborns).
Ventilating Tubes
 OAEs can be recorded in presence of
tubes, but not in 100% of ears.
 Fritsch et al., 2002: 81% of ears (out of 385)
showed TEOAEs postoperatively.
 Insufficient stimulus energy at 4 kHz.
 Owens et al., 1993: Ears with ventilating
tubes exhibited DPOAE amplitude lower
than amplitudes from healthy ears, but
higher than those of the untreated
diseased ears.
New Trend
 Combined OAE and tympanometry
devices (using the same probe).
OAE Analysis
 Not difficult if OAEs (TEOAEs and DPOAEs) were
first recorded with good technique under optimal
testing conditions (appropriate protocol, quiet
setting, quiet patient).
 The story is different if OAE testing was done in a
neonatal intensive care unit with a restless infant.
In that case, not only the data recording is more
difficult, but the interpretation of the test is also
more complicated.
Clinical
application of
OAEs and
Protocols
Cross-Check Principle
 Drs Jerger and Hayes, 1976: “no audiologic test
result should be accepted until it is confirmed
by an independent measure”.
 Principle was first based on behavioral
audiometry, immittance measures and ABR.
 The principle now incorporate the OAEs.
Triage
 Every new patient should be tested first with:
– Tympanometry (high frequency probe tone in
infants)
– Middle ear muscle reflex
– OAEs
Newborn Hearing Screening
Goal: Screen all types of Hearing Loss
Outer hair cells
Inner hair cells
Auditory
nerve
INSERM, Montpelier
Promenade ‘round the cochlea
Karl White, Ph.D.
Utah State University
Newborn Hearing Screening
 Is it necessary to evaluate the hearing
status of all newborns (NICU, full-term
babies)?
 How can we evaluate their hearing?
– Behavioral testing
– ABRs
– OAEs
 Are some protocols more useful than
others?
 Which equipment is the best?
High Risk Infants
Karl White, Ph.D.
Utah State University
Which OAEs for a good screening?
 For screening purposes both TEOAEs and
DPOAEs convey the same information .
Estimates at the frequencies of 2.0, 3.0 and
4.0 kHz have been established as good
descriptors of healthy peripheral
functioning.
 SOAEs: are not a useful tool as they are not
present in 100% of ears.
 OAEs are frequency-specific.
 OAEs are not modified by sleep stages.
 Possibility to record OAEs in less than a
minute
How to judge if the acquired OAE
response is normal (screening criteria)
 There is still no consensus on the screening criteria or their
corresponding values. Experience has shown that it is better to
divide the evaluation of the responses into two categories:
PASS or REFER.
 For the TEOAEs the majority of the UNHS programs utilize the
values of the S/N ratio as indicators, or the TEOAE
reproducibility at the frequencies of 2.0, 3.0, and 4.0 kHz. For a
PASS the reproducibility at ALL three frequencies should be
higher than 75% and the S/N ratios higher than 6 dB.
For the DPOAEs the screening criteria are protocol dependent
(65-55 is considered the default option). Usually the DPOAE S/N
values are estimated at 2.0, 3.0 and 4.0 kHz and if ALL three are
higher than 6 dB the case is assigned as a PASS.
Reducing Referral Rates
 To avoid high referral rates various
methods have been used, including:
 Maintaining an experienced group of
screening personnel (Spivak et al., 2000).
 Reducing ambient noise (Rhoades et al.,.
1999).
 Delaying age of testing as neonates older
than 24 hours are less likely to have
occluding vernix caseosa (Maxon et al.,
1997).
 Combined OAE and ABR screening (Prieve
and Stevens, 2000).
Limitations of OAE Screening
 OAEs are sensitive to outer hair cell dysfunction.
 OAEs can be reliably recorded in neonates in response to
stimuli in the frequency range above 1500 Hz. The OAE is
known to be sensitive to outer ear canal obstruction and
middle ear effusion and therefore, temporary conductive
dysfunction can cause a "refer" outcome in the presence
of normal cochlear function.
 Hearing screening in the neonatal period cannot identify
acquired or progressive hearing loss occurring
subsequently (also true for ABR screening).
Limitations to Newborn Screening
 Some infants with hearing loss will pass the newborn
hearing screening.
 Both ABR and OAE technology can show false-negative
findings, depending on whether hearing loss exists in
configurations that include normal hearing for one or
more frequencies in the target range. These would include
isolated low-frequency (i.e., below 1000 Hz) hearing loss or
steeply sloping high-frequency (i.e., above 2000 Hz)
hearing loss.
Auditory Neuropathy and Newborn
Hearing Screening
 If only OAEs are used as an initial screener, 10% of
children with HL who have normal OAEs also may have
serious auditory synchrony problems.
 Similarly, if only alternating polarity or single polarity
ABR is used as an initial screener, approximately 10% of
children with flat or abnormal ABRs will have normal
OAEs and may misdiagnosed.
 Children with ANSD are currently being found more
frequently because of the proliferation of newborn ABRbased hearing screening programs.
Genetic Hearing Loss
 OAEs can detect early cochlear dysfunction (site
specific).
 OAEs can detect subclinical auditory dysfunction
before it becomes apparent on the pure tone
audiogram.
 Early evidence of OAE abnormalities could help
predict which family member(s) is likely to
develop hearing loss in the future.
 OAEs are very useful for regular monitoring of
auditory dysfunction in individuals at risk for
hearing loss.
DPOAEs in Usher Carrier
and Matched Control Subject
From Hood et al., 1999
TEOAE Amplitude in Cx26 Carriers and
Matched Control Subjects
Cx 26 (n=15)
Control (n=15)
18
16
DPOAE Amplitude in dB
14
12
10
8
6
4
2
0
-2
-4
Right
Left
Ear
From Hood et al., 2001
Noise Induced Hearing Loss
 Noise causes changes in the function of the inner ear which
results in hearing loss: Noise Induced Hearing Loss (NIHL).
 Noise can also produce tinnitus.
 NIHL depends on duration of exposure and intensity.
 Noise Induced Hearing Loss can be
– Temporary: temporary threshold shift (TTS)
– Permanent: threshold stabilize at an elevated value: permanent
threshold shift (PTS)
 When NIHL is temporary, recovery occurs after hours, days
or weeks depending on initial severity.
 Noise-induced hearing loss (NIHL) is a major health problem
because opportunities for overexposure abound, and
exposures that damage hearing are not necessarily painful
or even annoying (music).
Kujawa and Liberman, 2009
Managing Musicians: The Use of Otoacoustic
Emissions in Monitoring Acoustic Trauma and
Counseling
Young woman with fifteen years of noise exposure to classical music
Acoustic Trauma
Similar audiogram with a much more robust transient OAE tracing of a young woman
of the same age with no history of noise exposure.
Counseling Musicians
The most effective demonstration is to personalize the effect of noise by testing a
musician's emissions before and after a loud concert thus demonstrating to them their
own temporary loss of outer hair cell function.
DP-gram of a young woman with
normal hearing.
Emissions the morning after a concert that
was reported to be "very loud". Note that
the reduction in DP amplitude is most
different between 3 and 4 KHz where
noise
has
its
biggest
effect.
Ototoxicity
 Two main classes of drugs that can cause permanent
hearing loss:
– Aminoglycoside antibiotics
– Platinum-based chemotherapeutic agents
 Chronic generation of reactive oxygen species (ROS)
 Drugs: Antioxidants and ROS scavengers
 Problem: Systemic administration of otoprotective
agent may interact with the drug and inactivate it.
 Cochlear targeted drug delivery is extremely difficult:
– Transtympanic injections
– Direct intracochlear application
Monitoring Ototoxicity
 OAEs:
– Highly sensitive to OHC dysfunction which are very
often affected first in ototoxicity.
– Earlier detection than behavioral audiometry
– Can be performed in young and sick patients
 DPOAEs are superior to TEOAEs because of their
extended high frequency limit. However, if time
allows, both TEOAEs and DPOAEs should be
performed (they represent 2 different mechanisms
of generation).
 One limitation is the higher incidence of otitis media
of patients receiving ototoxic medications.
 Some changes in OAEs might not be visible right
away. Follow-up recordings should be schedule even
months after administration of the drug.
Tinnitus
 Could be related to cochlear dysfunction
associated with either aging or noise exposure.
 Damage to outer and inner hair cells can lead to
disruption in the normal resting activity of
afferent auditory neurons. Subsequently,
reorganization of the function of higher auditory
centers may lead to tinnitus.
 OAE abnormalities are a common finding in
patients with tinnitus.
 But keep in mind that OAEs can also be normal in
some instances.
Pseudohypacusis
 OAEs are useful when an individual will not or
cannot voluntarily perform behavioral
audiometry.
 OAEs allow to resolve conflicts in findings (but
only after ruling out technical explanations, non
pathologic factors (patient didn’t understand the
task) and pathologic factors (IHC or neural
dysfunction).
 Pediatric patients with history of emotional
trauma and/or abuse are an example of patients
at risk for malingering.
OAEs and Neural Hearing Loss
 OAEs may or may not be present in patients with
space-occupying lesions affecting the VIIIth nerve
and/or caudal brainstem.
 Some patients with such neural lesions demonstrate
an absence of OAEs, most likely due to the restriction
of blood flow to the cochlea, which limits the oxygen
and nutrients needed by the cochlea.
 In addition to the effects on blood supply, neural
lesions may destroy cochlear fibers by pressure,
atrophy, or invasion and contribute to biomechanical
degradation of the fluids of the inner ear, thus
affecting hair cell and other cochlear processes.
 OAEs are usually present in cases of auditory
neuropathy.
Summary: Clinical Applications of OAEs
 OAE advantages:
–
–
–
–
–
–
–
–
Relatively short test time.
Ear specific audiologic information.
Frequency specific information.
Assesses cochlear function specifically.
Physiologic, not dependent on behavioral responses.
Can be recorded from sleeping and sedated children.
Monitoring ototoxicity: many ototoxic drugs exert their effect on OHC function.
Noise-induced HL: OHCs are extremely vulnerable to sound over-stimulation and
are the first to be affected amongst the hair cells.
– OAEs can detect cochlear dysfunction before it is evident by pure-tone
audiometry.
– Valuable contribution to the “cross-check principle.”
Summary: Clinical Applications of OAEs
 Pitfalls:
– Presence dependent on normal middle-ear function
– Need quiet test environment. OAEs are affected by
ambient and physiological noise which can limit use in
lower frequency ranges.
– Present in individuals with mild cochlear hearing loss,
neural losses.
– The fact that a subject has acceptable OAE responses at
the tested frequencies (PASS) does not IMPLY
automatically that the subject CAN HEAR.