Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Noise-induced hearing loss wikipedia , lookup
Audiology and hearing health professionals in developed and developing countries wikipedia , lookup
Sound from ultrasound wikipedia , lookup
Sensorineural hearing loss wikipedia , lookup
Olivocochlear system wikipedia , lookup
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: International Hearing Society 16880 Middlebelt Rd., Ste. 4 Livonia, MI 48154 • After your test has been graded, you will receive a copy of the correct answers and a certificate of completion. • All questions regarding the examination must be in writing and directed to IHS. • Credit: IHS designates this professional and development activity for one (1) continuing education credit. • Fees: $29.00 IHS member $59.00 non-member (Payment in U.S. funds only) ! TYMPANOMETRY Name ANSWER SECTION Address City State/Province Zip/Postal Code Email Office Telephone Last Four Digits of SS/SI# Professional and/or Academic Credentials Please check one: Payment: Charge to: o $29.00 (IHS member o $59.00 (non-member) o Check Enclosed (payable to IHS) o American Express o Visa o MasterCard o Discover (PHOTOCOPY THIS FORM AS NEEDED) Card Holder Name Card Number Signature 30 Exp Date (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