Continuing Education: TYMPANOMETRY Article...assessment of Tympanometry. ... Concha 250 500 1000 2000 4000 8000 20 10 0 . Figure 4. The resonances of the Outer and Middle ears serve

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Tympanometry is a non-behavioral test of middle ear function, which means it requires no voluntary response on the part of the client being tested. It can 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, air-bone 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 MiddleEars 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, which fills the outer two boney labyrinths is 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

Figure 2 shows that the middle ear in-creases 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

The purpose of this article is to describe the principles behind commonly used Tympanometry, how it is done, and how to interpret the results.

continuing education

Written by: Ted Venema

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)

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Figure 1. The Middle ear is a closed space and thus, quiteinaccessible to scrutiny from the outside.

Continuing Education:

TYMPANOMETRY

Figure 1. The Middle ear is a closed space and thus, quite inaccessible to scrutiny from the outside.

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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

it mathematically works out to an increase 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

be otitis media with fluid in the middle ear space or otosclerosis. This is why conductive HL can often be greater than 30-35 dB HL.

Outer and Middle Ear Resonances and SpeechFigure 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

Figure 3. The middle ear must increase the pressure of air-borne sound because the cochlea is filled with fluid!

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In Summary: 1. Eardrum – Stapes size: 17:1 2. Ossicles leverage action: 1.3:1 3. Eardrum buckling action: X 2:1

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Figure 3. The middle ear must increase the pressure of air-borne sound because the cochlea is filled with fluid!

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In Summary: 1. Eardrum – Stapes size: 17:1 2. Ossicles leverage action: 1.3:1 3. Eardrum buckling action: X 2:1

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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.

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best at around 2000 Hz, and the middle ear space has two other resonances of 750-900 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.

II. Tympanometry and the Middle Ear

Figure 5 shows that Tympanometry 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

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!

Why Does Tympanometry Typically Use a Low-Frequency Tone?With Tympanometry, we test the com-pliance 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

resonates with low frequencies. A low-frequency 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 low-frequency 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 low-frequency sound bounces off the TM.

continuing education ... cont’d.

Figure 6. The normal Tympanogram is shaped like a Tent.

Negative 0 Positive Air Pressure

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1.  Middle ear is most efficient when air pressure is equal on both sides of the TM.

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SPL is picked up by probe microphone, most is getting through to the Middle ear.

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pressure behind the TM must therefore be the same as that in the Outer ear canal.

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Figure 6. The normal Tympanogram is shaped like a Tent.


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1.  Middle ear is most efficient when air pressure is equal on both sides of the TM.

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SPL is picked up by probe microphone, most is getting through to the Middle ear.

3. At this peak, the air

pressure behind the TM must therefore be the same as that in the Outer ear canal.

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Figure 5. Tympanometry enables examination of the closed Middle ear space from the Outer ear canal.

Speaker Tone in

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Figure 5. Tympanometry enables examination of the closed Middle ear space from the Outer ear canal.

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The TympanogramFigure 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 low-frequency 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 low-frequency 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.

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

is to examine the physical properties of 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

226 Hz tone at 70 dB SPL went through 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 TypesThe 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


Figure 7. Tympanogram progressions with various stages of Otitis Media (OM). Type A = normal, Type C = early OM with negative Middle ear pressure, Type B = advanced OM with fluid.


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Figure 7. Tympanogram progressions with various stages of Otitis Media (OM). Type A = normal, Type C = early OM with negative Middle ear pressure, Type B = advanced OM with fluid.


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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” Tympano-gram, 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 ComplianceTympanograms show other middle ear pathology besides otitis media. Oto-sclerosis 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 com-pliance is found. Normally, this would be at an air pressure of 0 daPa. Static compliance thus works out to be the

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 excessive middle ear stiffness. Unlike otitis media, the air pressure is even on both sides of the TM. Tympanometry thus reveals a Type A Tympanogram with an abnormally low static compliance; the resultant short or squat Type A Tympanogram is called a “Type As.” On the other hand, disarticulated middle ear ossicles or a scarred and damaged TM which has become abnormally thin, will cause an abnormally over-compliant middle ear system. This is seen as a Type A Tympanogram with abnormally high static compliance; the resultant tall Type A Tympanogram is called a “Type Ad.”

Physical Volume TestingThe was originally intended to imitate the acoustic impedance of the closed ear canal. Most of us also know that when the adult ear canal volume is closed with an insert headphone or a hearing aid in place, its physical volume is smaller, and 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.

It can also be useful when interpreting a Type B Tympanogram. Maybe the Type B Tympanogram isn’t showing fluid build-up behind the TM. If the Type B Tympanogram is accompanied by an abnormally small volume, it is possible that the probe tip may be lodged against the client’s ear canal wall. That Type B 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 might suggest a perforated TM, because the abnormally large volume might just include not only the air space in the closed ear canal, but also the middle ear space too!

Acoustic Reflex TestingAcoustic 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


Figure 8. Physical Volume (PV) of ear canal is normally between 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, then probe tip is against Outer ear canal wall.



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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

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.

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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.

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Efferent Route V Nerve VII Nerve Tensor Tympani muscle (TT) Stapedius muscle (S)

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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.

Reporting AR Findings. The AR stimulus tones are calibrated and recorded on the Tympanometer in dB HL. AR findings or results however, are reported in dB sensation level (SL). If an AR is recorded with a 500 Hz tone at a stimulus level of 100 dB HL, it is reported in reference to the client’s own hearing threshold for 500 Hz. If the client’s threshold for 500 Hz is 0 dB HL, then the AR is reported as present at 100 dB SL. If the client’s

threshold for 500 Hz is 30 dB HL how-ever, 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.

AR Patterns. From our previous discussion of contralateral and ipsilateral AR’s, one can see that there are then four sets of AR’s that can be tested on a client: right ear contralateral & ipsilateral, and left ear contralateral & ipsilateral. In the heady

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.

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 the air pressure in the outer ear canal to whatever it was when the greatest middle ear compliance was found. Normally, this would be regular room air pressure (0 daPa). As in regular Tympanometry, the 226 Hz tone at 70 dB SPL is sent on into the ear canal while the probe microphone records some amount of the tone that bounces back off from the TM. At the same time, a loud low-frequency pure tone of 500 or 1000 Hz at 85 dB HL is briefly delivered by a separate headphone to the opposite ear. Recall that due to neural decussation or crossover, an AR is caused in both ears even though only one ear is stimulated. Recall also that the AR causes a temporary stiffening or reduced compliance, of the middle ear system. If there is a sudden increase of the 226 Hz tone picked up by the microphone in the probe ear, the Tympanometer records an


226 Hz tone to measure AR

500 or 1000 Hz AR stimulus tone

Ipsilateral ARs Came Later On

Figure 11. AR stimuli: 500 or 1000Hz tones at 85 to 110 dB HL Ongoing 226 Hz tone at 70 dB SPL in same ear measure AR! SPL increase at probe microphone indicate an AR.









Contralateral ARs were 1st to be Developed

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.

Contralateral ARs were 1st to be Developed

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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) Bilateral Conductive HL:contralateral and ipsilateral AR’s willlikely be absent for both ears.

b) Unilateral Conductive HL: ipsilateralAR would likely be present atnormal SL’s for the normal ear; allother AR’s would be absent. Whenthe loud stimulus tone is given tothe good ear, the contralateral ARwon’t occur in the bad ear due tothe mechanical problems in thatear. The contralateral AR’s andipsilateral AR’s from the bad earare both absent because the hearingloss in that ear prevents the ARstimulus tones presented to that earfrom being heard loudly enough tocause an AR.

c) Bilateral Mild-to-moderate SNHL:contralateral and ipsilateral AR’soften present but at reduced SL’s forboth ears.

d) Unilateral Mild-to-moderate SNHL:contralateral and ipsilateral AR’spresent at normal SL’s for the goodear. For the bad ear, contralateral andipsilateral AR’s will likely be presentbut at reduced SL’s.

e) Bilateral Severe-to-profound SNHL:contralateral and ipsilateral AR’s willlikely be absent for both ears.

f) Unilateral Severe-to-profoundSNHL: contralateral and ipsilateral

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 patternwould be similar to that for theunilateral severe-to-profound SNHL.

h) Low Brain Stem Tumor: ipsilateralAR’s would be present at normalSL’s, but due to decussation or neuralcrossover problems, the contralateralAR’s would likely be absent.

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 mild-to-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

About Ted Venema:

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.

Normal Inner

& Outer

Hair Cells

From Venema, T. Compression for Clinicians 2nd edition, Cengage 2006

Figure 12

Normal Inner

& Outer

Hair Cells

From Venema, T. Compression for Clinicians 2nd edition, Cengage 2006

Figure 12


30

1. The normal Tympanogram should showa peak at:a) 0 mmhob) 0 cc’sc) 0 mld) none of the above

2. The leverage action of the middle earossicles increases sound pressure by afactor of:a) 1.3:1b) 17:1c) 44:1d) 2:1

3. As you go down the Y axis of aTympanogram:a) audible probe sound gets softer for

the listenerb) the amount of sound bouncing back

to the probe decreasesc) the amount of sound going though

the TM increasesd) admittance increases

4. Otosclerosis may show a typeTympanograma) Abb) Acc) Add) As

5. If you could look at the Tympanogramwhen AR’s occur, you’d actually see atemporary:a) increase in the height of the

Tympanogramb) decrease in the height of the

Tympanogramc) negative air pressured) none of the above

6. For normal hearing, AR’s occur forsounds that are about dB SL.a) 100-120b) 80-100c) 60-80d) 40-60

7. What AR findings would likelyoccur with a unilateral moderateConductive HL?a) absent ipsilateral AR’s with present

contralateral AR’s for both earsb) present ipsilateral AR’s for the normal

ear, all other AR’s absentc) absent contralateral AR’s with present

ipsilateral AR’s for both earsd) present ipsilateral & contralateral

AR’s for the normal ear only

8. What AR findings would likely occurwith a unilateral severe-profoundSNHL?a) absent ipsilateral AR’s with present

contralateral AR’s for both earsb) present ipsilateral AR’s for the normal

ear, all other AR’s absentc) absent contralateral AR’s with present

ipsilateral AR’s for both earsd) present ipsilateral & contralateral

AR’s for the normal ear only

9. Severe SNHL in both ears is most oftenassociated with:a) AR’s at normal SL’s for both earsb) AR’s at reduced SL’s for both earsc) absent AR’s for both earsd) AR’s at elevated SL’s for both ears

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10. Two people have the same flat 50dBSNHL; one has AR’s, the other doesnot; the 1st will probably:a) show worse speech discriminationb) have a negative Tympanogramc) show better speech discriminationd) have a Type B Tympanogram

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