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10 Middle Ear Measurement in Infants and Children
2
c B
V
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
If the system were mass dominated, θY would be negative and the
admittance vector would be pointed down in the bottom right
quadrant (Fig. 10.2).
To circumvent the problem of trying to measure the middle
ear admittance with the added admittance of the ear canal as
measured at the plane of the probe tip, we can use vector tympanometry, a measurement of Ya as a function of ear canal pressure
(Fig. 10.3). In theory, the middle ear admittance is reduced to near
zero with high positive or negative air pressure in the ear canal.
What is left is the admittance of ear canal space, Yec. We can then
subtract Yec from the total admittance measured at the tympanometric peak to arrive at the admittance of the middle ear Yme, also
referred to as peak-compensated static acoustic admittance, peak
Ytm.12 Another clinically useful measurement of the vector tympa-
nogram is its width (TW) in dekapascals (daPa) measured at half
the height of peak Ytm calculated from the positive tail (Fig. 10.3).
where ρ (rho) represents the density of air and c equals the speed
of sound. Vea varies with frequency and, when measured in adult
ear canals, is positive at low frequencies and becomes negative at
high frequencies. Vea for a low-frequency probe tone is useful for
determining such things as the patency of pressure equalization
(PE) tubes or the possibility of a t ympanic membrane perforation.
Several studies have shown that wideband measurement
of the acoustic power or energy transfer to the middle ear
may yield a family of ATFs useful in pediatric middle-ear
assessment.
the ratio of the reected pressure to the incident pressure. Middle
ears with low admittance tend to reect more sound pressure
than they absorb. The energy reectance is the square of the
magnitude of the pressure reectance. The absorbance equals 1 –
energy reectance and represents the ratio of the energy absorbed
by the middle ear to the incident energy. Energy reectance and
absorbance are approximately the same no matter where along
the ear canal they are measured, and thus, these measures have an
advantage over admittance, which is more significantly aected
by the ear canal volume. The recommended term wideband
acoustic immittance (WAI) is used to refer to the family of both
wideband power- and impedance-based measures.
comparing these wideband measures with 1-kHz tympanometry
in newborns and from other work will be presented in subsequent
sections.
13,14,15,16,17,18,19,20,21,22
The acoustic pressure reectance is
23,24
Results
Fig. 10.3 Measurements made with a tympanogram include Vea, which
is the equivalent volume in cm
sated static acoustic admittance in millimhos (mmho); and TW, the
ympanometric width, which is the width of the tympanogram in daPa
t
measured at one-half its height.
3
; peak Ytm, which is the peak-compen-
Pitfall
Tympanometric width (TW), as described in this chapter and illus-
trated in Fig. 10.3, is calculated dierently than tympanometric
gradient, a ratio, and the two measurements dier in clinical
utility; tympanometric width is more diagnostically useful. Be
aware that some equipment manufacturers are not always clear
in how width and gradient are labeled. One way to discern the
dierence is by the unit of measurement used; tympanometric
gradient is a ratio but may be expressed in units of mL on some
devices, while tympanometric width is measured in daPa.
Another useful quantity, the equivalent volume (V
calculated in terms of the susceptance as:
a
=
ea
2
fρπ
), may be
ea
10.3 Conducting Middle Ear
Measurements
10.3.1 Otoscopic Examination
An otoscopic examination is essential prior to undertaking the
admittance evaluation. For young children and infants, it is often
helpful if the child sits on the parent’s lap during otoscopy and
subsequent admittance testing. The parent should be advised
that if little hands make a grab for the ear, the parent should
intercept. Prior to otoscopic examination, children are often
comforted to be shown that the clinician is holding a “ashlight”
and they can see the light shining on them. A cursory look into
the parent’s ears by the audiologist may also be reassuring for
the child. It is best not to ask permission of the child to look in
his ear; rather, just go about your business in a confident and
comforting manner, letting the child know what you are doing.
If the child is reluctant to let you perform otoscopy, you may be
able to complete the task with the help of an assistant who can
distract the child momentarily with an interesting toy, similar
to the role of a test assistant in behavioral testing. This toy distraction technique may also be useful during tympanometry and
ASR testing.
The appropriately sized speculum should be selected based on
an observation of the child’s external ear. The best view will be
obtained with a speculum tip slightly smaller than the ear canal
diameter, allowing it to be inserted into the canal while providing
the maximum lumen for viewing purposes. It is important to
create a bridge between the scope and the patient’s head with
the pinky and/or ring fingers of the hand holding the scope. This
bridge will allow your hand to move with sudden movements of
111
II Diagnosing Hearing Disorders in Infants and Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
the patient’s head rather than dislodging the speculum or pushing
it uncomfortably against the canal wall. The other hand may be
used to straighten the ear canal by gently pulling horizontally
backward on the pinna. This last step should be undertaken with
great care, especially if there is a history of ear pain.
Once the speculum is positioned in the canal, you may move
your eye close to the scope to view the canal. As you may have only
a quick look with some pediatric patients, it is important to see
whether the ear canal is (1) clear enough to allow the insertion of
an admittance probe tip; (2) free from excessive cerumen; (3) free
from other obstructions such as PE tubes that have been extruded
from the tympanic membrane; and (4) not draining excessively so
as to plug the probe. It is also important in this quick look to see
whether (1) the normal landmarks of the tympanic membrane
can be seen (light reex, umbo, and short process of malleus); (2)
the tympanic membrane appears normal or is inamed or perforated; (3) a PE tube appears to be in place or not; and (4) there
is any scarring or tympanosclerosis of the tympanic membrane,
which could lead to abnormal tympanometry.
10.3.2 Tympanometry
Preparing to Test
Daily calibration of the tympanometer with the included calibration cavities ensures valid test data. It is also helpful to check that
instrument defaults are to your liking when you work with other
audiologists. A self-administered tympanogram is also useful in
that it provides a biologic check and ensures that the system has
not developed an internal pressure leak. For pediatric assessment, one should have an admittance instrument capable of
multiple probe frequencies, and the calibration of each should be
checked per the manufacturer’s recommendations. The standard
226-Hz probe tone specified by ANSI S3.3912 may be used from
age 7 months to adulthood, but higher-frequency probe tones are
required to test young infants, as discussed subsequently.
Many tympanometers allow the examiner to adjust other test
parameters in addition to probe frequency. A rapid pressure
sweep rate, often available in a screening-test mode, may be useful
in obtaining data quickly in children. Some systems oer a rapid
sweep rate, such as 600 daPa/s, except near the tympanogram
peak, where the rate slows to 200 daPa/s. Care must be taken to
duplicate the probe frequency and sweep rate if test results are
tm
increases with pressure sweep rate.25 Otherwise, locally collected,
age-specific normative data are preferable. Many commercial systems oer a standard ear canal pressure range (e.g., +200 to –300
daPa) and an extended pressure range (e.g., +300 to –600 daPa).
The extended range is useful in detecting a tympanogram peak
in cases of extreme negative middle ear pressure, where rising
admittance is often noted with increasing negative pressure in the
standard pressure range, but the pressure limit is reached before
the tympanogram peak is observed. Extreme negative middle ear
pressure could help to explain the presence of normal hearing
in an ear with a at tympanogram obtained within the standard
pressure range. However, the extended pressure range should
be used judiciously, as the standard range is sucient for most
ears and is more comfortable for the patient, which increases the
likelihood that both ears will be tested.
Obtaining a Seal
The otoscopic examination provides an opportunity to judge
the size of the probe tip appropriate for the patient. A standard
admittance probe tip will be inserted in the ear canal to obtain a
hermetic seal and, thus, should be large enough to aord a snug
fit. If the clinician uses a screening tip, this will be held against
the canal during the test and should be larger than the canal
opening, but smaller than the concha bowl, for a good fit. With
some systems, t he tympanometer itself is a hand-held device that
is used with a screening probe tip held against the opening of
the ear canal. As with otoscopy, gently pulling horizontally back
on the pinna straightens the ear canal and makes it less likely
that it will be collapsed when the probe tip is inserted. Although
beginning clinicians often have diculty obtaining a hermetic
seal to complete the test and may be notified repeatedly that
there is a “leak,” the art of consistently obtaining an appropri-
ate seal comes with practice. However, on occasion, even the
most seasoned clinician will have diculty obtaining a seal for
tympanometry. If selecting a dierent probe tip does not solve
the problem, reexamine the ear with the otoscope to make sure
you have the correct angle on the ear canal when inserting the
probe tip. Note that an ear with a patent PE tube or a perforation
may register a very large equivalent volume including middle
ear and mastoid air cells as well as the ear canal. This volume
may exceed the measurable limit on some equipment, causing
the instrument to register a leak. Similarly, some equipment may
register a blocked probe in the presence of a normal but very
small ear canal volume, such as in an infant ear. It is important
to know these limitations for your equipment and to know the
upper and lower limits of measurable equivalent volume.
Most systems default to a starting pressure of +200 daPa
and then sweep pressure from a positive to negative direction.
However, the diculty in obtaining a seal may be increased by
starting the sweep with positive air pressure, as this may act to
push the probe out of the ear canal. When having diculty maintaining a seal, changing to a negative starting pressure may allow
a tympanogram to be obtained, because in this case the starting
pressure is not acting to push the probe out of the ear. However, it
should be noted that negative-to-positive pressure sweeps might
result in increased complexity of tympanogram shape.
Considerations When Testing Infants
Based on results from several studies, low-frequency tympanometry measurements are generally considered valid and
reliable predictors of middle ear function by about 7 months of
26,27,28,29
age.
changes in traditional immittance measurements in infants to
elucidate this issue.
Two studies of infants and children, with participants ranging
in age from 6 months to 4 years, reported a small but statistically
significant increase in static acoustic admittance and a decrease
in tympanometric width as a function of age.
conducted a longitudinal study of multifrequency tympanometry
in newborn infants through 4 months of age. They reported that
Several studies have investigated the developmental
30,31,32
25
29,30
Holte et al31
112
10 Middle Ear Measurement in Infants and Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
admittance magnitude stayed approximately the same across
age for a 226-Hz probe tone but increased with age at higher
frequencies (400 to 900 Hz). However, at all frequencies above
226 Hz, irregular tympanometric patterns were observed that
were inconsistent with the Vanhuyse model, which demonstrates the progression of tympanogram shapes with increasing
probe frequency in multifrequency tympanometry.27 Holte et
al31 showed that, by 4 months of age, tympanograms followed
the Vanhuyse model fairly consistently up to 900 Hz. They also
reported that, while general changes in development of Ytm and θY
were observed, these responses were characterized by substantial
intersubject variability.
Pearl
Unsure about the Vanhuyse model? A good reading of the
discussion by Hunter and Margolis27 will go a long way toward
improving your understanding of this model and demonstrate
just how important it is in interpreting tympanometry results.
To investigate suggestions that pressure-induced changes in the
external ear canal inuenced middle ear measurements, Holte et
31
introduced positive and negative pressure pulses in the ear
al
canal and used video monitoring to determine a percent change in
ear canal diameter relative to resting diameter. They found that the
pressure-induced change in ear canal diameter steadily decreased
as a function of age, dropping from an 18% change at 1 to 7 days to
no change at 4 months of age. They reported that in some cases,
where no ear canal wall motion was observed, there were still
multiple peaks in the 226-Hz tympanograms. Correlations that
were computed to assess the relationship between complexity of
tympanometric patterns and amount of wall distention failed to
reach significance. Based on this result, the authors suggested that
ear canal wall mobility and tympanometric patterns were not
related.
Meyer et al32 documented changes in Ya tympanograms for a
single infant using 226-Hz and 1,000-Hz probe frequencies. They
reported results similar to those of Holte et al,31 in that resonant
frequency progressed from low to high frequency with age. This
was evidenced by more complex tympanometric shapes observed
with a 226-Hz probe tone at younger ages. Results when using
a 226-Hz probe tone showed gradual change from complex to
simple tympanometric shapes with age, indicating a shift from a
mass- to a stiness-dominated middle ear system with age. The
opposite eect was observed for tympanometric results for the
1000 Hz probe tone, with tympanograms gradually changing
from simple to more complex with age. In addition, Meyer et
al32 reported a at 1,000-Hz tympanogram in conjunction with a
normal 226-Hz tympanogram during a period of time when the
infant presented with middle ear pathology.
Tympanogram Interpretation
Children Older Than 7 Months of Age
Single-frequency 226-Hz admittance-vector tympanometry is
universally used in clinical assessment for adults and children.
Tympanograms were initially interpreted qualitatively in
terms of pressure continua.
single-peaked shape, normal amplitude, and normal peak pres-
sure is a Type A. Type B is at, indicative of ears with eusion
or tympanic membrane perforation; Type C displays a peak with
excessive negative pressure (usually exceeding –150 to –200
daPa). Other subtypes were used to describe various conditions,
such as Type AS, normal pressure peak but abnormally shallow
amplitude, often seen in otosclerosis. Many audiologists and
physicians continue to refer to tympanograms using this system.
However, in addition to describing the shape of the tympanogram, most audiologists provide a quantitative assessment made
possible with the advent of calibrated admittance instruments
and ANSI S3.39.12 This allows for a quantitative assessment of
peak Ytm, TW, Vea, and tympanometric peak pressure (TPP).
The next step is to determine whether the tympanogram is
within normal limits. Some general guidelines will be provided,
but normative data collected with preferred instrumentation
settings is ideal. For all ages, at tympanograms, where Ytm is 0
mmho, are abnormal, with the caveat that a at tympanogram
with a standard pressure range may be masking an ear with
extreme negative pressure. Flat tympanograms with large equivalent volumes (Vea ≥ 1 cm3) are suggestive of a patent PE tube or a
perforation, and if pre- and post-PE-tube insertion measurements
are available, a change in Vea ≥ 0.4 cm3 suggests that the tube is
patent.35 These criteria were obtained with insert-type probe tips
with a 226-Hz probe tone as measured at +200 daPa in children
ranging from infancy to 7 years. A large Vea in an ear without a
tube is suggestive of a tympanic membrane perforation, and thus
a medical referral is indicated.
A at tympanogram with normal ear canal volume and a
tympanogram with an abnormally low peak Ytm or abnormally
wide TW are suggestive of middle ear eusion (MEE). Specifically,
Nozza et al36 found that a TW criterion of > 275 daPa had the best
test performance for detecting MEE in children 1 to 12 years of
age. For ages 6 to 30 months, a value of peak Ytm < 0.2 mmho is
suggestive of MEE. This is also the case for ears with peak Ytm ≥
0.3 mmho but TW > 235 daPa.29 These criteria were obtained
with an automatic tympanometer with a 226-Hz probe tone and
a +200 daPa compensation. American Speech-Language-Hearing
Association (ASHA)37 screening criteria suggest that children 1
year to school age should be referred for retest if peak Ytm < 0.3
mmho with a +200 daPa compensation or with TW > 200 daPa
(see also American Academy of Audiology [AAA]38 and Margolis
and Hunter3). TPP is an indicator of middle ear pressure and
should be reported. However, eorts to use TPP as a screening tool
and basis for referral have not been successful.
33,34
A tympanogram with normal
3
Children Younger Than 7 Months of Age
As noted previously, the young-infant middle ear is dominated
more by mass contributions than by stiness. While the exact
developmental time course is not known, 226-Hz tympanometry
113
II Diagnosing Hearing Disorders in Infants and Children
2 2
pt
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
measurements are, for the most part, adultlike by about 6 to 8
months of age and are generally considered valid predictors of
middle ear function.
10,27,29
Although research suggests that 1,000-
Hz tympanometry is more sensitive to changes in middle ear
status in infants than 226-Hz tympanometry is,
39,40
there is no
consensus regarding a single method for interpreting 1,000-Hz
tympanometric data. As with strategies for interpreting 226-Hz
tympanometry, both quantitative and qualitative methods have
been proposed.
Margolis et al41 and Kei et al42 evaluated 1,000-Hz tympanometry results and reported normative data, including compensated
admittance magnitude values. Margolis et al41 suggested a low
cuto value (5th percentile for peak-to-negative-tail compensated admittance) of 0.60 mmho, while Kei et al42 suggested a low
cuto value (5th percentile for peak-to-positive-tail compensated
admittance) of 0.39 mmho. Margolis et al used their suggested
pass/fail criterion of 0.60 mmho and assessed 1,000-Hz tympanometric test performance in predicting whether a newborn infant
passed or failed a distortion product otoacoustic emission (DPOAE)
test. Using the DPOAE test outcome as the reference standard, the
1,000-Hz test had a specificity of 91% but a sensitivity of only 50%.
The 1,000-Hz Ya tympanograms of a neonate who was referred
for failing a newborn DPOAE hearing screening for the right ear
as well as a secondary ABR screening with a click stimulus at 30
dB normalized hearing level (nHL) are shown in Fig. 10.4. The
infant passed both screening tests for the left ear. Note that the
right tympanogram is essentially at, while the left tympanogram
shows a relatively normal shape. The infant is being followed for
right ear conductive hearing loss, which is expected to be transient. Application of normative data from Kei et al42 and Margolis
et al41 to these results would result in a similar classification for
the right ear, but peak Ytm for the left ear falls in between the two
suggested criterion of 0.39 and 0.60 mmho, respectively.
A dierent quantitative analysis method proposed by Margolis
and Hunter43 utilizes the individual admittance components (conductance, G, and susceptance, B) to generate compensated admittance component values. Instead of simply subtracting the
admittance magnitude at the positive tympanogram tail from the
admittance magnitude at the tympanogram peak, the individual
component (G and B) peak-to-tail values are calculated, and then
the component compensated admittance (Ycc) is calculated as:
2 2
where
Y G B= +
cc pt pt
and pt are the squared peak-to-tail values for
pt
conductance and susceptance, respectively. The rationale for
using the individual components lies in the fact that for adults,
when a 226-Hz probe tone is used, the uncompensated peak
admittance and admittance at the positive tail have a similar
phase angle. However, when a 1,000-Hz probe tone is used in
an infant ear, the phase angles may not be the same. To estimate the admittance of the middle ear most accurately, it is
necessary to calculate admittance using individual admittance
components. Several studies have reported data obtained using
this analysis method
40,44,45
and suggested that the larger mean
admittance values produced with the compensation method
(versus admittance magnitude) may allow greater separation
between data obtained from normal and abnormal middle ears.
This method requires the “extraction” of B and G component
data; however, some immittance systems calculate and display
component-compensated tympanograms for the user.
Baldwin46 used a qualitative analysis method similar to one
first proposed by Marchant et al47 and a traditional visual classification system (Type A, B, etc.)
33,34
to assess middle ear function
in 2- to 21-week-old infants. For the Marchant et al47 method, a
line was drawn between the susceptance (B) tympanogram tails
at +300 and –400 daPa, and a peak susceptance was measured
from the baseline to the susceptance peak. Baldwin46 modified
this method and, instead, drew a line between the admittance
tympanogram tails at +200 and –400 daPa (Fig. 10.5). A middle
ear generating either positive- or negative-going admittance
tracings (e.g., “peaks”) relative to the drawn line between pressure extremes was classified as having either normal or abnormal
middle ear function, respectively; “indeterminate” tracings (with
both positive and negative peaks) were put in the negative peak
Fig. 10.5 Tympanograms obtained from the left ear of a 15-day-old
Fig. 10.4 The Ya 1,000-Hz tympanograms for a neonate who failed
newborn hearing screening for the right ear (dashed line) and passed on
the left ear (solid line). The peak Y
either +200 or –200 daPa compensation.
b
on the right was 0.53 mmho with
tm
infant using both 226-Hz and 1000-Hz probe tones. The 1,000-Hz
tympanogram on the right illustrates a qualitative method of
interpreting 1,000-Hz tympanograms in young infants; in this case,
a positive-going admittance tracing (relative to the horizontal line)
would suggest a normal middle ear.
114
category and were classified as having abnormal middle ear func-
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
tion. Tympanometry results obtained with 226-Hz, 678-Hz, and
1,000-Hz probe tones from 107 infants were organized using the
Lidén/Jerger types
The infants were grouped as having either normal or disordered
middle ear function based on results from a combination of air
and bone conduction ABR results and behavioral assessments. The
Baldwin method for classifying 1,000-Hz tympanograms provided
the best results, with sensitivity of 0.99 and specificity of 0.89.
This qualitative approach to classifying 1,000-Hz tympanograms
showed excellent test performance for dierentiating between
normal and abnormal middle ears for infants 2 to 21 weeks of age
and is simple to perform.
Both 226-Hz and 1,000-Hz tympanograms from the left ear of
a 15-day-old infant who passed a DPOAE screening are shown
in Fig. 10.5. In this case, the presence of the positive peak would
suggest that this ear has normal middle ear function; the 226-Hz
tympanogram appears normal too. Tympanograms from the right
ear of a 39-day-old infant are shown in Fig. 10.6. In this case, the
226-Hz tympanogram appears normal, but the presence of a negative-going admittance tracing with the 1,000-Hz tympanogram
(right panel) would suggest middle ear dysfunction; this result is
consistent with a failed DPOAE screening for the right ear.
While the need to use 1,000-Hz probe tone tympanometry for
young infants is clear and some normative data and interpretation
strategies have been published, to date there is no consensus on
which specific strategy is best. For a more in-depth review of
these interpretation strategies and a summary of normative data,
see the individual cited studies above and that by Kei and Zhao.
33,34
and the alternative (“Baldwin”) method.46
48
10 Middle Ear Measurement in Infants and Children
Fig. 10.6 Tympanograms obtained from the right ear of a 39-day-old
infant using both 226-Hz and 1,000-Hz probe tones. The 1,000-Hz
tympanogram (right panel) illustrates a qualitative method of
interpreting 1,000-Hz tympanograms in young infants; in this case,
a negative-going admittance tracing (relative to the horizontal line)
would suggest an ear with middle ear dysfunction.
results in absent reexes in the majority of neonates, whereas
with a 1,000-Hz probe tone, nearly all neonates have a measur-
able reex. Second, ipsilateral ASR activator signals are typically
calibrated in a 2-cm3 coupler to establish a dB HL value. This
calibration is not appropriate for infant ears and underestimates
the level of the reex activator in the infant ear canal. Otherwise,
it has been shown that ASR thresholds for children are similar to
those for adults. For more in-depth discussions and case study
presentations of ASR testing in infant populations, see Mazlan et
al,45 Kei,49 and Kei and Zhao,48 respectively.
Pitfall
Be careful interpreting equivalent ear canal volume (Vea) data
when conducting 1,000-Hz tympanometry tests. The straightforward relationship between physical volume and admittance
when using a 226-Hz probe tone (e.g., 1 cm3 volume of air has
an admittance of 1 mmho) does not hold true when using other
frequencies. Clinicians can use 226-Hz probe tone tympanometry to obtain Vea data and 1,000-Hz probe tone tympanometry
to interpret the admittance characteristics of the middle ear.
Alternatively, some equipment uses a calculation method to
estimate Vea when using probe tones other than 226 Hz; know
what your equipment capabilities are and how to interpret the
data.
10.3.3 Acoustic Stapedius Reex Testing
ASR testing typically follows tympanometry, using the same
equipment and probe placement, with ear canal pressure
adjusted to peak tympanometric pressure for maximum sensi-
tivity. For screening purposes, many systems oer an automated
search for the presence of a reex at several levels, stopping
when a criterion admittance shift is obtained (typically 0.02 or
0.03 mmho for a 226-Hz probe tone). Two important caveats
are related to ASR testing in young infants. A 226-Hz probe tone
Pitfall
To avoid confusion, when reporting contralateral ASR results, it is
helpful to specify which ear received the activator stimulus (e.g.,
“with the probe in the left ear and activator in the right ear, ASR
results were within normal limits”).
10.3.4 Wideband Acoustic Immittance
Tests
While wideband acoustic immittance (WAI) has application for
individuals of any age, the prevalence of middle ear dysfunction
and heightened need for objective, diagnostic tests in pediatric
populations increases the potential benefits of improved pediatric-driven middle ear assessment tools. Studies investigating WAI
and middle ear disorders have included a variety of pediatric populations, including newborns, infants, and children.50 In addition
to detection of middle ear dysfunction, WAI is also sensitive to
developmental changes in the ear canal and middle ear.
In an NHS population, Sanford et al19 examined the test performance of 1,000-Hz tympanometry and wideband absorbance
in predicting the conductive status (e.g., ear canal and/or middle
ear) of ears that passed or were referred in NHS tests based on
DPOAEs. The tests of conductive status in newborn ears included
measurements of 1,000-Hz tympanograms and wideband absorbance at ambient pressure, as well as wideband tympanograms
21,51
115
II Diagnosing Hearing Disorders in Infants and Children
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
(e.g., wideband absorbance measured in the presence of pressure
changes in the ear canal). The Pass group of one-day-old infants
included 375 ears, and the Refer group included 80 ears. The
median and interquartile range of the absorbance at ambient
pressure from Sanford et al19 are plotted in Fig. 10.7 for both the
Pass and Refer groups. Ears that passed the DPOAE screening
tended to have higher absorbance than Refer ears in the frequency
range of DPOAE testing. A receiver operating characteristic (ROC)curve analysis for this data revealed that wideband absorbance
was more accurate than 1,000-Hz tympanometry in predicting
DPOAE test outcomes in an NHS program.
A similar study by Hunter et al,15 with data from a large number of
infants, revealed that wideband energy reectance at ambient pressure at and around 2 kHz had the best test performance in predicting
which newborn infants passed or referred on a DPOAE test; the WAI
tests were also significantly better predictors than 1,000-Hz tympanometry. Using data from their study, Hunter and colleagues15 cre-
ated confidence intervals to indicate normative reectance regions
(1–6 kHz) for newborns and suggested that changes in reectance
at the 2-kHz region be used to determine a pass or refer test result.
Relationships between conductive hearing loss (CHL) and WAI
have been investigated
52,53,54
as well as the eects of otitis media
with eusion on WAI responses.55 Overall, results from these
studies indicate that the most pronounced eects on WAI tend to
be in the mid frequency range (e.g., 1,000–3,000 Hz), suggesting
that these frequencies may be diagnostically useful in helping
distinguish normal from abnormal middle ear function.
Although these wideband tests show promise as potentially
useful diagnostic tools, additional quantitative decision criteria
are needed to assist clinicians with data interpretation, along with
more normative data across wider age ranges and from ears with
a variety of middle ear disorders.
When an ASR occurs, there is a frequency-dependent shift in
admittance. In adults, the reex causes a decrease in admittance
at frequencies below ~ 700 Hz and an increase in admittance
above this frequency, with a positive peak admittance shift
around 1,000 Hz56 (Fig. 10.8). This shift as a function of frequency
is age dependent, although the time course for the development
of an adultlike ASR shift is not known. Using WAI tests, Feeney
and Sanford14 showed that, for 6-week-old infants, there was a
maximal negative shift in admittance at 1,000 Hz during a con-
tralateral ASR reex, compared with the maximal positive shift
for adults at that frequency (Fig. 10.8). Although the time course
is not known, the zero-crossing point will shift down in frequency
with development and, at some point, would occur near 1,000 Hz,
presumably making the reex dicult to detect with a 1,000-Hz
probe tone. It is suggested that a wideband probe signal such as a
chirp or click would be more successful in detecting a reex across
development in infants than a single frequency would.
Keefe et al57 investigated the usefulness of including a wideband ASR test as part of a wideband ATF test battery aimed at
classifying ears that passed or referred on an OAE newborn
hearing-screening test. ASR thresholds were obtained in 97% and
90% of infants who passed or were referred on an OAE screening
test, respectively. A wideband test battery, which included ASR
tests, showed improved test performance in predicting an NHS
outcome, relative to 1,000 Hz tympanometry and a wideband test
battery without ASR tests. However, the wideband test battery
with ASR was not significantly better at classifying ears than were
wideband tests without ASR included. Although not incorporated
into clinical immittance systems at this time, research studies
aimed at gathering additional data on acoustic reexes in infants
across the first 6 months of life, when the middle ear is undergoing significant change, will help further our understanding of
infant auditory development and reveal potential uses of ASR in
audiologic evaluation of infants.
11,57
Fig. 10.7 Ambient energy absorbance from newborn ears that passed
or referred on a DPOAE screening test. Shaded areas represent the
25th to 75th percentile ranges, with the light gray shading representative of the Pass group and the dark gray shading representative of
he Refer group. Dashed and solid lines represent the 50th percentile
t
(median) for the Refer and Pass groups, respectively.
Fig. 10.8 The average shift in admittance as a function of frequency
during the contralateral ASR for ve infants from Feeney and Sanford
and 58 ears for 34 adults from Feeney et al.
normalized by dividing the shift by the baseline admittance (ΔY = [ |Y|
activator – |Y| baseline]/|V| baseline). Note that at 1,000 Hz there was
a maximal positive shift in admittance for the adults and a maximal
negative shift in admittance for the infants.
56
The reex shifts were
116
14
10.4 Conclusion
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
In this chapter we have covered the fundamental principles and
clinical components of the pediatric immittance test battery,
including tympanometry, stapedial acoustic reex, and wideband acoustic immittance tests. Because of the anatomic development of the conductive mechanism of the peripheral ear over
the first few months of life, alternative stimuli, test methods, and
normative data are needed to determine middle ear status in
infants and young children. Information regarding the application of these pediatric-based test procedures and methods may
be added to the clinician’s toolbox for implementing middle ear
measurements in infants and children.
Discussion Questions
1. What components constitute a vector tympanogram, and
how do they relate to the function of the middle ear?
2. What quantitative and qualitative descriptors should be used
to report on the results of vector tympanometry?
3. Is there a reason to obtain special middle ear measurement
equipment for pediatric assessment? Why or why not?
4. You are seeing a 5-year-old child who recently had PE tubes
inserted. His hearing has improved in one ear, but he continues to have a conductive hearing loss in the other ear. The
otoscopic examination reveals that the tubes appear to be
in place in both ears. What can admittance measurement
contribute to the assessment of this child?
5. An 18-month-old is referred to you for a hearing evaluation
by his pediatrician because of parental concern that he hasn’t
started to talk. You are unable to condition the child for VRA,
but you obtain normal 226-Hz tympanograms and normal
OAEs. In addition to rescheduling the child for repeat behavioral assessment, what additional test(s) should be conducted
or scheduled?
Acknowledgments
The authors thank Monica Feeney for the preparation of figures. The content of this chapter does not represent the views
of the Department of Veterans Aairs or of the United States
Government.
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11 Otoacoustic Emissions: Applications for Pediatric Audiology
Madell et al., Pediatric Audiology: Diagnosis, Technology, and Management, 3rd Ed. (ISBN 978-1-62623-401-7),
copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.
11 Otoacoustic Emissions: Applications for Pediatric
Audiology
Sriram Boothalingam, Uzma Shaheen Wilson, and Sumitrajit (Sumit) Dhar
Summary
Otoacoustic emissions (OAEs) have become an indispensable tool
for pediatric audiology. They are the only practical tool available to
the clinician for an evaluation of the cochlea in isolation. Their use
ranges from newborn hearing screening to dierential diagnosis.
The great advantages of OAEs revolve around the ease of testing,
the objectivity of the results, and the clear connection to active
processes in the cochlea. While OAEs are in widespread use in
pediatric audiology today, their full potential remains unrealized.
New knowledge related to the generation and propagation of OAEs
continues to be d iscovered. This new k nowledge is expecte d to yield
even more powerful clinical applications for OAEs in the coming
years. In this chapter, we review the current state of knowledge
about and application of OAEs in pediatric audiology. We focus
on clinical protocols for a variety of purposes and illustrate established methods of data interpretation. Various types of OAEs and
their clinical applications are discussed as well. We end the chapter
with a forward-looking section on anticipated developments.
Keywords
otoacoustic emissions, OAEs, cochlea, screening, dierential
diagnosis
Key Points
Otoacoustic emissions are an essential byproduct of the
•
cochlear amplication processes and thus serve as a very
sensitive indicator of general cochlear health.
Otoacoustic emissions can be classied either by the type of
•
stimulus us ed to record them or by t heir generation m echanism.
Although otoacoustic emissions reect cochlear health, they
•
are signicantly inuenced by the acoustics of the ear canal as
well as forward and reverse transmission through the middle
ear.
Otoacoustic emissions play a critical role in both screening
•
(e.g., newborn, school age) and diagnostic (e.g., ototoxicity)
protocols.
11.1 Physiology of Otoacoustic
Emissions
Otoacoustic emissions (OAEs), sounds generated in the cochlea
and recorded in the ear canal, provide us a window into the complex hydro-mechano-electrical puzzle that is the inner ear. Since
their discovery,1 OAEs have significantly boosted our understanding of cochlear physiology. Furthermore, they are noninvasive and quick, requiring neither much patient preparation
nor a voluntary behavioral response from the patient. OAEs have
proven to be particularly beneficial in newborn/infant hearing
screenings and other pediatric applications. The combined use
of OAEs and auditory brainstem responses (ABR) has revolutionized early detection and intervention for hearing loss, leading to
significantly improved language outcomes. In this chapter, we
aim to provide a reference for pediatric audiologists on utilizing
OAEs in screening and diagnosis of cochlear malfunction (often
associated with hearing loss). We start the chapter by discussing cochlear physiology pertinent to OAE generation; then we
describe OAE measurement techniques, highlight specific uses
in pediatric audiology, and present current clinical norms. We
recommend full textbooks
cation of OAEs for readers interested in diving deeper.
OAEs are an essential by-product of the cochlear amplification
processes and thus serve as a very sensitive indicator of general
cochlear health, particularly outer hair cell (OHC) electromotility.
Several lines of evidence demonstrate a strong relationship
between OHC health and OAEs. For instance, toxins that specifically target OHCs eradicate OAEs,
nerve and inner hair cells (IHCs) intact. Damage to the OHCs
due to noise exposure also manifests as a reduction, or complete
loss, of OAEs, sometimes in the presence of clinically normal
audiograms.
those evoked by the interaction of two pure tones) are produced
by the nonlinearities associated with stereociliary transduction in
OHCs,9 but their generation at low stimulus levels is dependent on
the presence of somatic electromotility.
7,8
More recent evidence suggests that OAEs (at least
2,3
dedicated to the science and appli-
4-6
while leaving the auditory
10
Pearl
OAEs are not a test of hearing. They reect the health of OHCs,
given that outer and middle ear function is also intact. The
clinical value of OAEs is high because hearing loss is commonly
related to OHC dysfunction.
Simply put, OAEs are essentially runaway energy that is
generated during the cochlear amplification processes. As this
energy travel backs through the middle ear, it can be measured
as acoustic energy in the ear canal using a sensitive microphone.
The following conditions must be met for OAEs to be successfully
recorded: (1) The external ear must be free of significant obstruction, (2) the middle ear must transfer energy forward (from the
ympanic membrane to the oval window for the evoking stimulus
t
to enter the cochlea) and in reverse (for the OAE to exit the cochlea
and vibrate the tympanic membrane), and lastly, (3) both passive
basilar membrane and active OHC mechanics must be operational.
Recording normal OAEs depends on much more than just healthy
OHCs. Particularly relevant to pediatric populations, experimental
manipulation of the ear canal and middle ear pressure significantly
119
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reduces OAE amplitudes at frequencies below 2 kHz.11 Injecting
saline or amniotic uid in the chinchilla middle ear, simulating
common middle ear conditions in humans, also causes reduction
in OAE levels.12 A clinician must be able to dierentiate absent OAE
due to conductive reasons from that due to cochlear or OHC pathology. This is especially important in infant hearing screening, con-
sidering newborns’ middle ears may be filled with uid. Specificity
for detecting normal cochlear function improves when newborns
are screened 24 to 48 hours postpartum, or when the vernix has
13,14
cleared.
first few months, or even years, of life, primarily because of the
dramatic developmental changes in the outer and middle ears.
We provide guidance on interpreting OAE test results in various
age groups later in the chapter. However, there is no denying the
importance of clinical insight and interpretation of results across
various tests to reach an audiologic diagnosis accurately.
OAE levels continue to uctuate significantly in the
15,16
11.2 Classication of OAEs
Traditionally, OAEs have been broadly classified as “evoked” or
“spontaneous,” with a further classification of evoked OAEs based
on the type of stimuli used to evoke the response. OAEs evoked by
a single pure tone are called stimulus frequency OAEs (SFOAEs),
while those evoked by the interaction of two pure tones are called
distortion product OAEs (DPOAEs). A third type, evoked by transient stimuli (e.g. click, chirp, tone bursts, tone pips), are called
transient-evoked OAEs (TEOAEs). Of the dierent types of emissions, TEOAEs and DPOAEs are most commonly used clinically.
11.2.1 Transient Evoked Otoacoustic
Emissions
TEOAEs were the very first OAEs reported in the literature1 and
have since become a routine clinical tool. TEOAEs are measured
in response to a train of clicks with strict response criteria that
segregate the OAE signal from noise. Several clinical instruments
also enable the clinician to set artifact rejection criteria and
keep count of the number of responses rejected for noisiness.
The waveforms recorded in response to each click stimulus are
compared to provide the clinician with an estimate of waveform
reproducibility, either globally or in specific frequency bands
(Fi g . 11.1). As will be discussed later, these metrics serve as
quality markers of the acquired data.
Clinical information about cochlear health is gleaned primarily
from the spectrum where TEOAE levels are displayed as a function
of frequency along with the noise oor. Many clinical instruments
will also condense this information into a single estimate of the
TEOAE level in a frequency band along with an estimate of the
noise oor. TEOAEs evoked using clicks have broad frequency
content between 0.5 and approximately 5 kHz, limited by the
frequency response of the transducers. Clinical norms for TEOAE
levels to expect from a functional cochlea are available
often can be displayed on the results of some clinical instruments.
Click levels between 70 and 90 dB peak sound pressure level
(peSPL) are typically used to record TEOAEs, which are almost
always absent once hearing loss exceeds 30 dB hearing level
17,19
(HL).
This property of TEOAEs makes them a rather sensitive
17,18
and
tool to dierentiate between normal hearing ears and those with
greater than mild or moderate hearing loss. However, like other
OAEs, TEOAEs are less accurate in identifying ears with mild
hearing loss. This is largely due to the variability in TEOAE levels
recorded from normal hearing ears and those with mild hearing
loss, resulting in significant overlap between these distributions.
11.2.2 Distortion Product Otoacoustic
Emissions
DPOAEs20 are generated when two tones, at frequencies f1 and f2
(where f1 < f2), simultaneously deect OHC stereocilia. Because
the receptor current is nonlinearly related to the magnitude
of stereociliary deection, intermodulation distortion of the
current is coupled into the basilar membrane or cochlear uid
vibrations. This distortion energy at many predictable combinations of f1 and f2 can be then recorded in the ear canal as
DPOAEs. Of main clinical interest is the DPOAE at the 2f1 – f2
frequency. The characteristic frequency place for this DPOAE
on the basilar membrane is apical to those for f1 and f2, as it is
lower in frequency than either of the stimulus tones. Thus, while
much of the distortion produced at the f2 place travels toward
the base of the cochlea, part of the distortion energy travels to
its characteristic frequency place on the basilar membrane (i.e.,
toward the apex). This secondary energy is then reected back,
and the DPOAE ultimately recorded in the ear canal is a mixture
of two DPOAE components, typically referred to as the distortion
and reection components (details later).
Clinical DPOAE recordings are made using an f2/f1 ratio of approx-
imately 1.22, as this frequency relationship has been demonstrated
to yield DPOAEs of significant amplitude21 between 1 and 4 kHz.
Moderate levels, 65 and 55 dB SPL for the lower (L1) and higher (L2)
stimulus tones, respectively, are typically chosen. Using stimulus
tones fixed in frequency ratio and levels, DPOAE recordings are
made at a number of frequencies, resulting in the DP-gram: the
prototypical display of DPOAE level versus f2 frequency, along
with the noise oor (Fig. 11.2). As with TEOAEs, clinical norms
have been established for DPOAEs22 and are typically displayed in
clinical instruments to help guide clinicians in their diagnosis.
In an alternate protocol that is growing in popularity, DPOAE
input-output (IO) functions can be measured at a fixed f2 frequency over a range of stimulus levels, spanning a range of 60
to 80 dB SPL. These DPOAE IO functions can be used to estimate
behavioral hearing thresholds, with this predictive accuracy
improving with the development of sophisticated data-processing
strategies.
ship between the two stimulus tones changes with overall level
in a frequency-specific manner.25 Generally, the lower the overall
level, the greater the desired dierence between L1 and L2. DPOAEs
recorded using dierent stimulus levels appear to be dierentially
sensitive to dierent pathologies. For example, DPOAEs recorded
using lower stimulus levels are often more sensitive to changes in
cochlear function due to noise exposure. On the other hand, using
higher stimulus levels allows the recording of DPOAEs even from
ears with mild to moderate hearing loss (often up to 50 dB HL).
compared, especially in newborn hearing screening, with results
indicating that neither test performs best at all frequencies, but
23,24
It is important to note that the ideal level relation-
The clinical sensitivities of DPOAEs and TEOAEs have been
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