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Continuing Education:
TYMPANOMETRY
Figure 1. The Middle ear is a closed space and thus, quite
inaccessible to scrutiny from the outside.
Written by: Ted Venema
continuing education
The purpose of this
article is to describe
the principles behind
commonly used
Tympanometry, how
it is done, and how to
interpret the results.
Take the Quiz
on page 30
to earn 1 Continuing
Education Credit
22
Tympanometry is a non-behavioral test
of middle ear function, which means it
Figure 1. The Middle ear is a
requires no voluntary response on the
inaccessible
to scrutiny
part
of the client being
tested. It canfrom
be
routinely utilized by the HIS clinician
in private practice, and should become
a regular part of a client test battery. As
health care professionals know, one cannot
base conclusions on one single test. As
math teachers always say, “It takes two
dots to make a line.” In our field, airbone gaps seen in Pure Tone Testing can
be backed up by a quick, five-minute
assessment of Tympanometry.
The purpose of this article is to describe
the principles behind commonly used
Tympanometry, how it is done, and how
to interpret the results. The general thrust
here is to familiarize clinical practitioners,
in the clearest way possible, with generally
known and widely accepted procedures of
Tympanometry.
I. Why Do We Have Middle
Ears in the First Place?
Figure 1 (above) shows the middle ear is a
closed space, filled with air. One purpose
of the middle ear is to change or transduce
incoming sound waves into mechanical
piston-like energy. The cochlea of the
inner ear is filled with fluids called
perilymph and endolymph. Perilymph,
closed
space and thus, quite
which fills the outer two boney labyrinths
theisoutside.
similar to the fluid that surrounds the
brain; namely, cerebral-spinal fluid. The
inner membranous labyrinth is filled
with endolymph, which has the opposite
chemical composition. The job of the
cochlea is to transduce fluid motion
energy into electrical energy, because this
is the “language” the brain understands.
The Middle Ear Increases
Sound Pressure
2.
2.
1.
3.
Buckling action
TM at rest
Umbo
1.
Figure 2. The Middle Ear Increases Sound Pressure 3 Ways:
1. TM is larger than footplate of Stapes (17:1)
2. Leverage action of ossicles (Malleus is 1.3:1 longer than Incus)
3. Buckling action of TM (2:1)
Figure 2 shows that the middle ear increases the pressure of airborne sound so
that it can activate the fluid-filled cochlea.
Airborne sound cannot otherwise activate
a fluid-filled cochlea. Think of having your
head under water in a swimming pool as
120
In Summary:
1. Eardrum – Stapes size:
2. Ossicles leverage action:
3. Eardrum buckling action:
100
you try to hear someone speaking who is
standing on the edge. You won’t hear much
because almost all of the airborne sound
will bounce off the water. The same would
happen if we didn’t have middle ears.
Almost all of the mechanical energy from
the middle ear would bounce off from the
cochlea. The middle ear increases sound
pressure in three ways. First, the working
surface area of the tympanic membrane
(TM) is 17 times larger than the footplate of
the stapes which sits inside the oval window,
the entrance to the cochlea. Pressure is
force over an area. To appreciate this, push
hard with your whole palm of your hand
against your cheek and feel the pressure.
Now push against your cheek with the same
force using just your finger tip. You’ll feel
lots more pressure. It’s the same reason why
a sharp knife cuts through bread. In the
middle ear, force upon the large TM area
is converged onto a much smaller area of
the stapes, and this increases the pressure
by 17 times. Second, the middle ear ossicles
are shaped the particular way that they are,
so they can act like a lever. The malleus
is 1.3 times as long at the long process of
the incus. This increases the pressure by
a factor of 1.3:1. Third, the TM itself does
not move as a whole in exactly the same
way. When activated by airborne sound, it
buckles, such that parts of it move more
than other parts. This increases the pressure
by a factor of 2:1.
Figure 3 (above top) shows how these
three pressure increases multiply together,
and also how this translates into a decibel
(dB) increase. The total pressure increase
(17 X 1.3 X 2) works out to something
close to 44:1. Readers may recall from past
studies of sound that if sound pressure is
increased by 10 times, there is a 20 dB
increase; if the pressure increase is 100:1,
there is a pressure increase of 40 dB. The
44:1 pressure increase offered by the
middle ear is between 10:1 and 100:1, and
80
dB
SPL 60
In Summary:
33dB
1. Eardrum – Stapes size:
2. Ossicles leverage action:
3. Eardrum buckling action:
80
dB
SPL 60
17:1
1.3:1
20
X 2:1
44:1
This corresponds to an increase between 30-35 dB
0
40
33dB
This corresponds to an increase between 30-35 dB
40
120
100
17:1
1.3:1
X 2:1
44:1
0
20
10
100
1000
10,000
100,000
1,000,000
44:1 1,000,000 Pressure
Pressure
44:1
Figure
3. The
must increase the pressure of air-borne
Figure 3. The
middle ear must
increase middle
the pressure ofear
air-borne
sound because the cochlea is filled with fluid!
sound because the cochlea is filled with fluid!
0
0
10
30
30
100
1000
10,000
100,000
30
30
Total Ear Canal
Total Ear
& Canal
&
Concha
Concha
20
20
+
20
20
10
10
30
10
0
10
10
0
0 250
250
Total Ear Canal
&
Concha
20
500
500
500
1000
100030
1000
2000
2000
4000 8000
4000
8000
Middle Ear
0
0 250
250
500
500
1000
1000
2000
2000
4000
4000
8000
8000
+4040
20
=
=
250
Middle Ear
Middle Ear
2000
40
dB 25
SPL10
Note how important speech Hzs
Note how important speech Hzs
dB
8000
500
1000 2000 4000 8000
are emphasized
dB
are emphasized
SPL10
SPL
Note how10
important speech Hzs
10
4000
25
0
25
250
are
0 emphasized
0
0
125
250
8000
500
Hz
125
125 2000
1000
250
250
8000
8000
4000
Figure 4. The resonances of the Outer and Middle ears serve to
create an equal loudness curve that shows our best hearing
sensitivity is between 1000 to 4000 Hz.
500
500
Hz
Hz
1000
1000
2000
2000
4000
4000
Figure
Figure 4.
4. The
The resonances
resonances of
of the
the Outer
Outer and
and Middle
Middle ears
ears serve
serve to
to
create
create an
an equal
equal loudness
loudness curve
curve that
that shows
shows our
our best
best hearing
hearing
sensitivity
is
to
it
mathematically
works out to 1000
an increase
be otitis media with fluid in the middle
sensitivity
is between
between
1000
to 4000
4000 Hz.
Hz.
of somewhere between 30-35 dB.
One might think then that the maximum
conductive hearing loss (HL) would
be between 30-35 dB HL. As we know
however, a conductive HL due to otitis
media (OM) or otosclerosis can easily be
more than this. How? Any pathology that
prevents the stapes from pushing into the
oval window, and consequently bulging
out the round window, will add even
more dBs to the HL than the middle ear
normally provides. Examples here could
ear space or otosclerosis. This is why
conductive HL can often be greater than
30-35 dB HL.
Outer and Middle Ear
Resonances and Speech
Figure 4 (above) shows that our outer and
middle ears actually improve our hearing
for the high-frequency consonants of
speech. The middle ear ossicles resonate
continued on page 24
23
continuing education ... cont’d.
Speaker
Tone in
Air Pressure
Speaker
changes
Tone in
Microphone
Air
Pressure
Tone
out
changes
Microphone
Tone out
Figure 5. Tympanometry enables examination of the closed
Middle ear space from the Outer ear canal.
Figure 5. Tympanometry enables examination of the closed
Middle
ear space
from thethat
OuterTympanometry
ear canal.
Figure
5 shows
involves the use of a probe inserted into
the ear canal with a tight seal, so that
no air can leak out. The assumption
behind Tympanometry is that in order
for the middle ear to be most efficient at
passing incoming sounds through it, air
pressure should be even on both sides
of the TM. Contrary to common belief,
Tympanometry does not determine “how
much the eardrum wiggles.” The probe
has three holes in it to provide: 1) a tiny
speaker, 2) a tiny microphone, and 3) a
way to change air pressure. The client
can feel these air pressure changes during
the test. During the air pressure changes,
a steady low-frequency tone at 70 dB
sound pressure level (SPL) is presented
through the probe speaker, and the probe
microphone picks up whatever sound
bounces back off from the TM. If the least
amount of sound bounces back off the TM
when the air pressure in the outer ear canal
is at regular room air pressure, this means
24
Why Does Tympanometry
Typically Use a LowFrequency Tone?
With Tympanometry, we test the compliance of the middle ear by measuring the
amount of low-frequency tone reflecting
off the stiff middle ear as a function
of air pressure changes. Compliance
is the opposite or inverse of stiffness.
Tympanometry uses a low-frequency tone
because the middle ear is a “stiffness
dominated system.” The middle ear system,
which involves the TM and ossicular chain,
is always stiff, but it is least stiff when
the air pressure is even on both sides of
the TM. The middle ear ossicles are tiny
and therefore, do not have much mass.
Stiffness is therefore the main source of
opposition to the passage of sound through
the middle ear. Stiffness opposes the
passage of low frequencies and resonates
with high frequencies, while mass opposes
the passage of high frequencies and
1.  Middle ear is most efficient High
when air pressure is equal
on both sides of the TM.
2. When least probe tone
SPL is picked up by
probe microphone,
Least SPL picked up
probe microphone
most
is High
gettingbythrough
1.  Middle ear is most
efficient
when air pressure is equal
the
on both sidesto
of the
TM. Middle ear.
2. When least probe tone
SPL is picked up by
probe microphone,
most is getting through
to the Middle ear.
3.
resonates with low frequencies. A lowfrequency tone is used so that some sound
will bounce off from the TM, even when
the middle ear is least stiff. If it didn’t,
the sound would pass through the TM
and there would be nothing left for us to
measure!
Now consider the normal situation, when
the air pressures inside the outer ear
canal and the middle ear space are both at
regular room air pressure. When the lowfrequency Hz tone is presented at 70 dB
SPL, some of it will pass through the stiff
middle ear system, but because the middle
ear is a stiffness dominated system, some
of it will bounce back off the TM. With
positive or negative air pressure in the
outer ear canal however, the air pressure
is made to be different from that inside
the middle ear space, and this makes the
normally stiff middle ear system become
stiffer yet. In these situations, even more
sound bounces off the TM and less goes
through it. In other words, with uneven
air pressure on both sides of the TM, the
Middle ear is made temporarily more
stiff than it usually is and therefore, less
efficient. Consequently, more of the lowfrequency sound bounces off the TM.
Least SPL picked up
by probe microphone
Compliance
II.Tympanometry and the
Middle Ear
the air pressure behind the TM is the same.
In this way, Tympanometry measurement
in the outer ear canal tells us about the
middle ear air pressure behind the TM!
Compliance
best at around 2000 Hz, and the middle
ear space has two other resonances of 750900 Hz and 1200 Hz. The outer ear canal
resonance falls roughly between 1500 and
4000 Hz. Together, the outer and middle
ears thus serve to create the human
hearing sensitivity curve, which shows our
very best hearing sensitivity to be between
1000-4000 Hz. This all contributes to
better hearing for speech.
3. At this peak, the air
pressure behind the
At this peak, the air
TM must therefore
be
pressure behind the
Most SPL picked up
TM must therefore be
Low
by probe mic
the same
Low as that in the
the same as that in the
Outer ear canal.
Outer ear canal.
Negative
0
Positive
Air Pressure
Most SPL picked up
by probe mic
Negative
0
Air Pressure
Positive
Figure 6. The normal Tympanogram is shaped like a Tent.
Figure 6. The normal Tympanogram is shaped like a Tent.
Type A
High
Type C
Why we don’t simply use “dB SPL
bouncing back” as a unit for the vertical
axis? Tympanometry measures the
reflectance of a 226 Hz tone with air
pressure changes, so one might ask why
the vertical axis of the Tympanogram
does not simply read in “dB SPL bouncing
back.” The purpose of Tympanometry
Type A
High
Type C going to Type B
Type C
Compliance
Figure 6 (below left) shows the
Tympanogram as a “tent-shaped” graph.
The horizontal axis shows negative,
neutral, and positive air pressure. The
air pressure units on the horizontal axis
are either mm H2O or dekaPascals (daPa).
These pressure units are essentially
the same in value. The vertical axis
shows compliance (inverse of stiffness),
from minimum at the bottom towards
maximum as you go up the axis. The
compliance units have often been
designated in millilitres (ml) or cubic
centimetres (cc’s) of air. These units are
rather confusing however, because they
don’t intuitively convey stiffness to the
average clinician. We thus use a different
term today. Recall that middle ear
stiffness opposes the passage of the lowfrequency tone. The Ohm is a unit used to
describe opposition and resistance. Since
compliance is the inverse of stiffness, the
word “ohm” is simply flipped around to
read “mho.” The ear is small however, and
so the “mho” is too large a unit to use.
This is why we use thousandths of a mho
or millimhos (mmho’s) to indicate units
for compliance on the vertical axis of
the Tympanogram. Incidentally, the lowfrequency tone used in Tympanometry
has the specific frequency of 226 Hz. This
is mainly done for calibration reasons.
At regular sea-level air pressure, the
compliance of a 1 cc of air to a 226 Hz
tone is exactly one mmho.
Compliance
The Tympanogram
Type B
Low
Type C going to Type B
Type B
Low
Negative
Negative
Air Pressure
Air0 Pressure
0
Positive
Positive
Figure 7. Tympanogram progressions with various stages of
Otitis Media
Type A = normal, Type Cprogressions
= early OM with
Figure
7. (OM).
Tympanogram
with various stages of
negative Middle ear pressure, Type B = advanced OM with fluid.
Otitis Media (OM). Type A = normal, Type C = early OM with
negative
Middle
ear pressure,
B = 226
advanced
fluid.
is to examine
the physical
propertiesType
of
Hz tone atOM
70 dBwith
SPL went
through
the middle ear. As a stiffness dominated
system, we want to test its stiffness (or
compliance) per se. Also, if we reported
the Tympanogram in terms of amount of
dB SPL bouncing back, the amount would
vary hugely across individuals, and so
would the size of resultant Tympanograms!
This is because different probe insertion
depths change the ear canal volume in
any one person; furthermore, ear canals
themselves vary in size across individuals.
Measuring compliance in units of mmhos
renders similar sized Tympanograms
independently from the depth of probe
insertion or ear canal size. It allows for a
fairly standard range of Tympanogram size
and shape to be used as normative. The
thing to remember is that changes in dB
SPL bouncing back off the TM correspond
to changes in compliance; the less sound
that bounces back, the more compliance
you have.
The normal Tympanogram has a peak
showing greatest compliance over
neutral or 0 regular room air pressure.
Compliance increases (stiffness decreases)
as you go up the vertical axis. The normal
Tympanogram indicates that when the
air pressure in the Outer ear canal was
at neutral room air pressure, some of the
the TM and some of it bounced back and
was picked up by the probe microphone.
The “tails” of the normal Tympanogram
are situated at positive and negative air
pressures. These show that when Outer
ear canal air pressure was made either
positive or negative, relatively more sound
bounced off the TM and less went through
it. If we follow this logic, to the client
being tested, audibility of the 226 Hz tone
would normally be greatest at 0 regular
room air pressure, and softest at positive
and negative air pressures.
III.Four Tests Done with
Routine Tympanometry
There are four tests that are performed
during routine Tympanometry. These are:
1) classification of Tympanogram Types,
2) Static Compliance, 3) Physical Volume
testing, and 4) Acoustic Reflex testing.
Tympanogram Types
The top of Figure 7 (above) shows several
Tympanograms. The top-most one is the
normal Tympanogram, and it is called a
“Type A.” It shows the good news that the
air pressure behind the TM is at regular
continued on page 26
25
continuing education ... cont’d.
neutral room air pressure, and that there
is no Middle ear vacuum or pressure
buildup. Middle ear pathology of almost
any kind will instantly become apparent
with Tympanometry. For example, in
early stages of otitis media, there is
negative air pressure behind the TM.
Negative air pressure in the outer ear
canal therefore, will make air pressure
even on both sides of the TM. The top
left Tympanogram shows this negative
middle ear pressure, because it has a peak
that hovers over negative air pressure.
This Tympanogram is called “Type C.”
As otitis media advances, fluid becomes
built up behind the TM. As a result, the
Type C Tympanogram begins to develop a
rounded peak, as is shown by the middle
left Tympanogram. When increased fluid
buildup behind the TM continues, the
Tympanogram will begin to show no
peak at all. This is a “Type B” Tympanogram, and it is shown at the bottom left.
A “Type B” Tympanogram means that
no air pressure change in the outer ear
canal can result in maximum middle
ear compliance.
Static Compliance
Tympanograms show other middle ear
pathology besides otitis media. Otosclerosis and other types of middle
ear pathology such as damaged TMs
and disarticulated ossicles can also
be indicated. Here we get into what is
known as “Static Compliance.” Static
compliance can be described as the
difference between maximum and
minimum compliance of the middle ear.
First, the compliance of the middle ear
is determined at positive + 200 daPa air
pressure. Next, compliance is determined
at the air pressure where greatest compliance is found. Normally, this would
be at an air pressure of 0 daPa. Static
compliance thus works out to be the
26
height of the Tympanogram.
As a middle ear pathology, oto-sclerosis is
a hereditary condition where soft porous
boney growth surrounds the footplate of
the stapes, which prevents it from moving
easily in and out of the oval window. In
this case, it is not negative air pressure or
a fluid buildup that causes an abnormal
Tympanogram; Oto-sclerosis creates
Figure 8. Physical Volume (PV) of ear canal is n
1.0 to 1.5 cc. A large PV might indicate a perfor
excessive middle ear stiffness. Unlike
Type B Tympanogram has normal PV. If Type B
otitis media, the air pressure is even on
then probe tip is against Outer ear canal wall.
both sides of the TM. Tympanometry
Figure 8. Physical Volume (PV) of ear canal is normally between
thus reveals a Type A Tympanogram with
1.0 to 1.5 cc. A large PV might indicate a perforated TM. True
Type B Tympanogram has normal PV. If Type B with tiny PV,
an abnormally low static compliance;
then probe tip is against Outer ear canal wall.
the resultant short or squat
Type
A
Figure
8. Physical
Volume (PV) of ear canal is normally between
to 1.5As.”
cc. AOn
large PV might
perforated
TM.
True
Tympanogram is called 1.0
a “Type
It canindicate
also bea useful
when
interpreting
a
Type
B
Tympanogram
has
normal
PV.
If
Type
B
with
tiny
PV,
the other hand, disarticulated middle ear
Type B Tympanogram. Maybe the Type
then probe tip is against Outer ear canal wall.
ossicles or a scarred and damaged TM
B Tympanogram isn’t showing fluid
which has become abnormally thin, will
build-up behind the TM. If the Type B
cause an abnormally over-compliant
Tympanogram is accompanied by an
middle ear system. This is seen as a Type
abnormally small volume, it is possible
A Tympanogram with abnormally high
that the probe tip may be lodged against
static compliance; the resultant tall Type
the client’s ear canal wall. That Type B
A Tympanogram is called a “Type Ad.”
Tympanogram is then suspicious to begin
with. Then again, it is possible to see a
Type B Tympanogram along with an
abnormally large ear canal volume. This
The was originally intended to imitate
might suggest a perforated TM, because
the acoustic impedance of the closed ear
the
abnormally large volume might just
canal. Most of us also know that when
include not only the air space in the
the adult ear canal volume is closed with
closed ear canal, but also the middle
an insert headphone or a hearing aid in
ear space too!
place, its physical volume is smaller, and
Physical Volume Testing
actually closer to 1.5 cc’s. Since the 2cc
coupler is larger than the typical adult
closed ear canal, 2cc coupler measures
with a hearing aid tend to underestimate
the amount of SPL that the same hearing
aid would actually produce in the ear
canal.
Figure 8 (above) shows Physical Volume
testing during Tympanometry. This test
can be especially useful to get an instant
awareness of the client’s ear canal size.
Acoustic Reflex Testing
Acoustic Reflex (AR) testing utilizes
Tympanometry in a unique way. Instead
of stiffening the middle ear system with
positive or negative air pressures, AR
testing stiffens the middle ear system with
loud, low-frequency pure tones. When
the loud tone causes an AR, the result
is a temporary decrease in middle ear
compliance. The AR is read as a decrease
in static compliance. One could think of
Brain Stem
CN
TT
TT
VIII
nerve
SOCs
V
Nerve
Loud
Sound
Brain Stem
CN
TT
VIII
nerve
S
VII
TT
Nerve
SOCs
Afferent
Route
V
V
Nerve
Nerve
Loud incoming
sound
Loud
Sound
Middle
ear
VII
VII
Nerve
Nerve
Cochlea
S
S
VIII
Nerve
Afferent Route
Efferent Route
Loud incoming sound
V Nerve
Cochlear
Nucleus
(CN)
Middle ear
VII Nerve
Cochlea
Tensor Tympani muscle
(TT)
Superior Olivary Complexs
(SOCs)
VIII Nerve
Stapedius muscle (S)
V
Nerve
VII
Nerve
S
Efferent Route
V Nerve
VII Nerve
Tensor Tympani muscle (TT)
Stapedius muscle (S)
Figure 9. The Acoustic Reflex arc includes an afferent (going to
the brain) path and an efferent (going from the brain stem) path
back to the Middle ears. Note the crossover; a loud sound to one
ear causes an AR in both ears.
Cochlear Nucleus (CN)
Superior Olivary Complexs (SOCs)
Figure 9. The Acoustic Reflex arc includes an afferent (going to
the brain) path and an efferent (going from the brain stem) path
back to the Middle ears. Note the crossover; a loud sound to one
ear causes an AR in both ears.
the AR as causing a temporary decrease
in the height of the Tympanogram.
Figure 9 (above) shows the AR arc. The
AR test can be best appreciated with an
understanding of the AR itself, and its
anatomy and physiology. As an arc, the
AR has a loop or circuitous route, with
an ear-to-Brain Stem going (afferent)
section and a Brain Stem back-to-ear
(efferent) section. If a loud (85 to 110 dB
HL) low-frequency sound hits the TM, the
normal reaction is to have an AR. What
is the AR? It is a reflex which is always
an involuntary reaction to something. In
the case of an AR, a loud low-frequency
sound causes the reaction of two middle
ear muscles that pull on the ossicles. The
smaller but stronger of the two muscles is
the stapedius. It pulls outward on the neck
of the stapes to keep it from going in and
out of the oval window. The weaker and
yet larger of the two is the tensor tympani.
It pulls inward on the malleus to reduce
the vibration of the TM. The AR thus
works to momentarily tense the whole
middle ear system. For a split second, the
AR thus renders the middle ear more stiff
(less compliant and thus less efficient) at
conducting its mechanical energy to the
cochlea.
The AR involves nearly all parts of the
ear; namely, the outer, middle, inner, VIII
nerve, and brain stem. Note that three
cranial nerves are involved in the AR:
the V, VII, and VIII. As we know, the
VIII nerve is a sensory afferent nerve,
sending neural information of sound to
the brain. It takes cochlear information
from the afferent Inner Hair Cells (IHCs)
and sends this information to the cochlear
nucleus of the brain stem. From there,
neural information goes to the Superior
Olivary Complex (SOC) of the same side
(ipsilateral) and also to the opposite SOC
(contralateral). This crossover is called
“decussation,” and it explains why a loud
sound to one ear normally causes an AR
to occur in both ears. From the brain stem
SOC’s, an efferent message is sent to the
V and VII cranial nerves. The V nerve is
partially sensory (afferent) for feeling in
the face, and partly motor (efferent) for
activating muscles, one of them being the
Tensor Tympani. The VII nerve is a totally
efferent motor nerve activating the cheek
muscles as well as the stapedius muscle.
Incidentally, Bell’s palsy is a compromise
of the VII nerve. At any rate, this whole
afferent/efferent loop is known as the
AR arc.
The AR is a low-frequency phenomenon,
which helps to explain why we have
ARs in the first place. The AR is elicited
or caused by loud low-frequency tones,
such as 500 or 1000 Hz. Many clinicians
believe that the AR works as a natural
protection against loud sounds and that
it helps to reduce noise induced hearing
loss. Actually, the AR helps to reduce
what is known as the “upward spread of
masking.” Low frequencies mask high
frequencies better than highs mask lows.
This is why background noise which is
mostly low in frequency content, serves as
an unfortunately effective masker for the
high-frequency consonants of speech.
Have you ever noticed when you hear a
recording of your own voice, you are the
only one who thinks you sound so weird?
Others however, think the recording
sounds just fine. This is because when
you hear yourself in a recording, you
hear yourself in the way that others hear
you. While you talk, you hear yourself
by air conduction and also by bone
conduction. Others hear you only by way
of air conduction. The intensity of normal
ongoing speech by air conduction is about
65 dB SPL. You hear the intensity of
your own air plus bone-conducted voice
however, closer to 85 dB SPL, and this
is enough to cause an AR. The vowels
of speech are the loudest, and these are
mainly low in frequency. We basically
have AR’s to help reduce the upward
spread of masking from the vowel sound
of our own voices. The AR therefore
allows us to better hear high frequencies
continued on page 28
27
continuing education ... cont’d.
around us while we talk. The AR is also
caused by chewing, and also of course by
other outside intense low-frequency pure
tones and noise.
st to
Contralateral
Developed
Contralateral
ARsARs
werewere
1st 1to
bebeDeveloped
Figure 10. AR stimuli: 500 or 1000Hz tones at 85 to 110 dB HL.
These are presented with headphone.
Ongoing 226 Hz tone at 70 dB SPL in opposite ear
measures AR. SPL increase at probe microphone indicates an AR.
AR. If the 85 dB HL tone does not cause
an AR, the intensity is increased to 90
dB HL, than to 95 dB HL, etc., until an
AR is elicited. AR’s are always reported
according to the ear that received the loud
low-frequency pure tone. For example, a
loud sound put into the left ear causing an
AR in the right ear, is called a “Left ear
Contralateral AR.”
Figure 11 (below) shows the Ipsilateral
AR. When looking at these, it is easy
to see why the Ipsilateral AR’s were
developed later on. Here, the ongoing
226 Hz probe tone at 70 dB SPL, and
also the loud, brief low-frequency AR
stimulus tones are put into the same ear
canal at the same time! The challenge for
Ipsilateral AR testing is to eliminate any
phase interaction between the probe tone
and the AR stimulus tones. As with the
Contralateral AR, the Ipsilateral AR is
said to occur if there is a sudden increase
of the 226 Hz tone picked up by the probe
microphone.
threshold for 500 Hz is 30 dB HL however, then the AR is reported as present
at 70 dB SL. In any client and in any ear,
the AR findings might be reported as:
1) Present at normal SLs (85 – 110 dB HL),
2) Present at reduced SLs (from 20 to 85
dB SL), or 3) Absent.
AR Findings and HL. In general, normal
hearing renders both contralateral and
ipsilateral AR’s present at normal SLs.
Conductive HL most often results in
Absent ARs. Conductive HL tends to
obliterate AR’s for two reasons: a) like
a plug in the ear, the Conductive HL
prevents the AR stimulus tones from
being heard loudly enough to cause an AR,
or b) the middle ear pathology prevents
the mechanical muscle contraction of
the AR itself. Mild-to-moderate SNHL
often presents with AR’s at reduced SL’s,
and this is consistent with recruitment.
Recall that with SNHL, there is nothing
mechanically wrong with the middle
ears. As such, present AR’s at reduced
SL’s is a very good and normal finding for
SNHL. In general, the greater the SNHL,
the less the SL at which an AR will be
found. There is an almost direct inverse
relationship with degree of SNHL and the
SL for an AR. This relationship continues
until the SNHL becomes greater than
about 60 dB HL. Once the SNHL gets
to be worse than about 60 dB HL, the
AR’s are often absent. This is because
the severe degree of SNHL in that ear
prevents the AR stimulus from being loud
enough to cause an AR. VIII nerve and
low brain stem tumors also tend to result
in Absent AR’s.
Figure 10 shows the Contralateral
AR. The earliest AR’s were elicited
contralaterally, and it is easy to see why.
The manner in which ARs are tested
is actually quite amazing. With the
probe held in place in the ear canal, the
Tympanometer automatically adjusts
Reporting AR Findings. The AR stimulus
the air pressure in the outer ear canal to
tones are calibrated and recorded on the
whatever it was when the greatest middle
Tympanometer in dB HL. AR findings
ear compliance was found. Normally, this
or results however, are reported in dB
would be regular room air pressure (0
sensation level (SL). If an AR is recorded
daPa). As in regular Tympanometry, the
with a 500 Hz tone at a stimulus level of
226 Hz tone at 70 dB SPL is sent on into
100 dB HL, it is reported in reference to
the ear canal while the probe microphone
the client’s own hearing threshold for 500
records some amount of the tone that
Hz. If the client’s threshold for 500 Hz is
bounces back off from the TM. At the
0 dB HL, then the AR is reported as
same time, a loud low-frequency pure
present at 100 dB SL. If the client’s
tone of 500 or 1000 Hz at 85 dB HL is
briefly delivered by a separate headphone
Ipsilateral
ARs Came
Later
On Later On
Ipsilateral
ARs
Came
Ipsilateral ARs Came Later On
to the opposite ear. Recall that due to
226 Hz tone
Hztone
tone
ARHz
neural decussation or crossover, an AR isto measure226
226
to
AR
to measure
measure AR
caused in both ears even though only one
AR Patterns. From our previous discussion
ear is stimulated. Recall also that the AR
of contralateral and ipsilateral AR’s, one
causes a temporary stiffening or reduced 500 or 1000 Hz
AR stimulus
500tone
or 1000 Hz
AR
stimulus
tone
can
see that there are then four sets of
compliance, of the middle ear system. If
500 or 1000 Hz
AR stimulus tone
AR’s that can be tested on a client: right
there is a sudden increase of the 226 Hz Figure 11. AR stimuli: 500 or 1000Hz tones at 85 to 110 dB HL
AR at
stimuli:
tones
at 85 to
110 dB HL
measure
AR!
226 Hz11.tone
70 dB500
SPLorin1000Hz
same ear
tone picked up by the microphone in the OngoingFigure
ear contralateral & ipsilateral, and left ear
Ongoing
226 Hz
tone at 70indicate
dB SPLan
in AR.
same ear measure AR!
SPL increase
at probe
microphone
Figure
11.
AR
stimuli:
500
or
1000Hz
tones
at
85
to
110
dB
HL
SPL increase at probe microphone indicate an AR.
probe ear, the Tympanometer records an
contralateral & ipsilateral. In the heady
Ongoing 226 Hz tone at 70 dB SPL in same ear measure AR!
SPL increase at probe microphone indicate an AR.
28
About Ted Venema:
days of the 70’s and 80’s, audiologists
were required to memorize patterns of
AR findings and relate these to unilateral
versus conductive HL, unilateral versus
bilateral SNHL, VIII nerve tumors, etc.
Today we have CT scans and MRI’s that
can help to detect the presence of various
types of pathology but in the 70’s and early
80’s these procedures were only beginning.
Consider now the following AR patterns
with the following types of pathology:
a) B
ilateral Conductive HL:
contralateral and ipsilateral AR’s will
likely be absent for both ears.
b) Unilateral Conductive HL: ipsilateral
AR would likely be present at
normal SL’s for the normal ear; all
other AR’s would be absent. When
the loud stimulus tone is given to
the good ear, the contralateral AR
won’t occur in the bad ear due to
the mechanical problems in that
ear. The contralateral AR’s and
ipsilateral AR’s from the bad ear
are both absent because the hearing
loss in that ear prevents the AR
stimulus tones presented to that ear
from being heard loudly enough to
cause an AR.
c) B
ilateral Mild-to-moderate SNHL:
contralateral and ipsilateral AR’s
often present but at reduced SL’s for
both ears.
d) Unilateral Mild-to-moderate SNHL:
contralateral and ipsilateral AR’s
present at normal SL’s for the good
ear. For the bad ear, contralateral and
ipsilateral AR’s will likely be present
but at reduced SL’s.
e) B
ilateral Severe-to-profound SNHL:
contralateral and ipsilateral AR’s will
likely be absent for both ears.
f) U
nilateral Severe-to-profound
SNHL: contralateral and ipsilateral
Ted Venema earned a BA in Philosophy at Calvin College in 1977, and an
MA in Audiology at Western Washington University in 1988. After working
for three years as a clinical Audiologist at The Canadian Hearing Society
in Toronto, he went back to school and completed a PhD in Audiology
at the University of Oklahoma in 1993. He was an Assistant Professor at
Auburn University in Alabama for the next two years. From 1995 until
2001, he worked at Unitron Hearing in Kitchener Ontario Canada, where he
conducted field trials on new hearing aids and gave presentations, domestically and abroad.
He also taught in the Hearing Instrument Specialist (HIS) program at George Brown College in
Toronto Canada, from 1995 until 2004. From 2001 until 2006, Ted was an Assistant Professor
of Audiology at the University of Western Ontario. As of 2005, Ted created and began
Canada’s 4th and most recent HIS program at Conestoga College in Kitchener, Ontario. This
full time program is now 5 years old. He continues to give presentations on hearing, hearing
loss and hearing aids. Ted is the author of a small textbook, Compression for Clinicians.
This book was updated and released as a 2nd edition in 2006.
AR’s present at normal SL’s for the
good ear. Contralateral and ipsilateral
ARs would be absent for the bad ear.
g) VIII Nerve Tumor: The AR pattern
would be similar to that for the
unilateral severe-to-profound SNHL.
h) Low Brain Stem Tumor: ipsilateral
AR’s would be present at normal
SL’s, but due to decussation or neural
crossover problems, the contralateral
AR’s would likely be absent.
Figure
Figure 12
12
Normal
Normal
Inner
Inner
&
&
Outer
Outer
Hair
Hair Cells
Cells
From
FromVenema,
Venema,T.
T.
Compression
Compression for
for
Clinicians
Clinicians22ndnd edition,
edition,
Cengage
Cengage2006
2006
AR’s and Speech Discrimination. Figure
12 shows normal IHC’s and Outer Hair
Cells (OHCs). Recall from the previous
discussion on the AR arc that the IHCs
of the Cochlea are afferent, meaning
that they send information to the VIII
nerve, toward the brain. The OHCs are
very different, in that they serve to help
the afferent IHCs sense soft input sounds
below 50 dB SPL. Most cases of mildto-moderate SNHL result from damage
primarily to the OHCs, and these hair
cells are not at all involved in the AR arc.
Severe SNHL results from damage to both
IHC’s and OHCs, and this is why ARs are
absent in these cases.
As clinicians, we have all encountered
people with similar degree of hearing
loss who have vastly different Speech
Discrimination (SD) scores. Have you
ever wondered why? Consider two people
with the same degree of mild-to-moderate
SNHL; one has good SD scores while
the other has poor SD scores. It is very
possible that the person with the better SD
performance has mainly OHC damage.
This client will likely have AR’s that are
present at reduced SL’s. Some cases of
mild-to-moderate SNHL however, result
from a mixture of IHC and OHC damage,
and here there is some involvement in
the AR arc. IHC damage implies that
the cochlea sends a mixed-up message
towards the brain. This client will likely
also have absent AR’s. n
continued on page 30
29
IHS Continuing Education Test
1.
The normal Tympanogram should show
a peak at:
a) 0 mmho
b) 0 cc’s
c) 0 ml
d) none of the above
2.
The leverage action of the middle ear
ossicles increases sound pressure by a
factor of:
a) 1.3:1
b) 17:1
c) 44:1
d) 2:1
3.
As you go down the Y axis of a
Tympanogram:
a) audible probe sound gets softer for
the listener
b) the amount of sound bouncing back
to the probe decreases
c) the amount of sound going though
the TM increases
d) admittance increases
4.
Otosclerosis may show a type
Tympanogram
a) Ab
b) Ac
c) Ad
d) As
5.
If you could look at the Tympanogram
when AR’s occur, you’d actually see a
temporary:
a) increase in the height of the
Tympanogram
b) decrease in the height of the
Tympanogram
c) negative air pressure
d) none of the above
6.
For
normal hearing, AR’s occur for
sounds that are about
dB SL.
a) 100-120
b) 80-100
c) 60-80
d) 40-60
7.
What AR findings would likely
occur with a unilateral moderate
Conductive HL?
a) absent ipsilateral AR’s with present
contralateral AR’s for both ears
b) present ipsilateral AR’s for the normal
ear, all other AR’s absent
c) absent contralateral AR’s with present
ipsilateral AR’s for both ears
d) present ipsilateral & contralateral
AR’s for the normal ear only
8.
What AR findings would likely occur
with a unilateral severe-profound
SNHL?
a) absent ipsilateral AR’s with present
contralateral AR’s for both ears
b) present ipsilateral AR’s for the normal
ear, all other AR’s absent
c) absent contralateral AR’s with present
ipsilateral AR’s for both ears
d) present ipsilateral & contralateral
AR’s for the normal ear only
9.
Severe SNHL in both ears is most often
associated with:
a) AR’s at normal SL’s for both ears
b) AR’s at reduced SL’s for both ears
c) absent AR’s for both ears
d) AR’s at elevated SL’s for both ears
10. Two people have the same flat 50dB
SNHL; one has AR’s, the other does
not; the 1st will probably:
a) show worse speech discrimination
b) have a negative Tympanogram
c) show better speech discrimination
d) have a Type B Tympanogram
For continuing education credit, complete this test and send the answer
section at the bottom of the page to:
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• After your test has been graded,
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correct answers and a certificate
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examination must be in writing
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(Circle the correct response from the test questions above.)
1. a
b
c
d
6. a
b
c
d
2. a
b
c
d
7. a
b
c
d
3. a
b
c
d
8. a
b
c
d
4. a
b
c
d
9. a
b
c
d
5. a
b
c
d
10. a
b
c
d