Our expert presenter today, Dr. Ted Venema, Ph.D., professor at Conestoga College in Kitchener, Ontario. Ted earned his B.A. in Philosophy at Calvin College in 1977 and his M.A. in Audiology at Western Washington University in 1988. After working for three years as a clinical audiologist at the Canadian Hearing Society in the University of Oklahoma in 1993. He was an assistant professor at Auburn University in Alabama from 1993-1995 and taught the Hearing Instruments Specialist Program at George Brown College in Toronto, Canada from 1995-2004. From 2001-2006, Ted was assistant professor of Audiology at the University of Western Ontario. In 2005, Ted created and began Canada's fourth and most recent Hearing Instruments Specialist Program at Conestoga College in Kitchener, Ontario, where he currently teaches. Ted is also the author of a textbook, Compression for Clinicians. We are very excited to have Ted as our presenter today. But before we get started, we have a few housekeeping items. Please note that we are recording today's presentation so that we may offer it on demand through the IHS website in the future. This webinar is available for one continuing education credit through the International Hearing Society. You can find out more about receiving continuing education credit at our website, IHSinfo.org. Click on the webinar banner on the home page, Choose Webinars, from the Professional Development menu on the left side of the page. There you'll find the CE quiz and information on how to submit it for credit. Also on the webinar page, IHS site, you'll find a note-taking guide to help you gather the information you'll need for the CE quiz. If you haven't already downloaded it, feel free to do so now. Tomorrow, you will receive an email with a link to a survey on this webinar. It is brief and your feedback will help us create valuable content for you moving forward. Today, we'll be covering the following topics along with Q&A within a 60-minute presentation. Learn why we have middle ears in the first place. Discover the principles behind tympanometry and how it is done. Discover how to interpret tympanograms to discern what type of conductive hearing loss is indicated. At the end, we'll move on to a Q&A session. You can send us a question for Ted at any time by entering your question in the question box on your webinar dashboard, usually located to the right of your webinar screen. We'll take as many as we can in the time we have available. Now I'm going to turn it over to Ted who will guide you through today's presentation. Ted? Hello, and welcome to the seminar, everybody. We'll be talking about tympanometry and why it should be used by the hearing instrument practitioner. I'm going to try and advance my slides, but for some reason I'm having difficulty doing it. Now I got her. At any rate, we'll move through these house keeping things that were already covered here. Everyone still with me? What we want to talk about is why we've got middle ears in the first place. That's something people don't speak about often enough, in my opinion. We can discover the principles behind tympanometry and how it is done, and learn how to interpret tympanograms to discern types of conductive hearing loss as would be indicated. See, the nice thing about tympanometry is it can be used by the clinician to back up the finding of an air bone gap, air conduction versus bone conduction. When you see a difference, tympanometry is a quick, five-minute, non-behavioral test whereby to further explain what's going on in that middle ear. So question and answers of course at the very end. Tympanometry impedance, sometimes it's called impedance, sometimes tympanometry, sometimes emittance, all kinds of terms, but it normally consists of a family of about four different tests. Tympanogram types is the first test or area that we'll look at regarding tympanometry. Secondly, we'll briefly discuss static compliance. And thirdly, the physical volume of the external auditory meatus, also known as the ear canal. Now these first three tests are done rapidly in succession on the instrumentation you've got when you're running a tympanogram. You don't separately run each of these. The probe in the ear just automatically cycles right through these. Now the fourth one, acoustic reflexes, that's a slightly different kettle of fish. And we unfortunately will not be covering that one today because there simply isn't the time slot in this time slot whereby to do that. Mind you, if IHS is kind enough to invite me back again, I'd gladly do another webinar on acoustic reflexes. But for now today, let's look at tympanometry regarding types of tympanograms, static compliance, and physical volume of the ear. The middle ear and what it does. Why do we have a middle ear? Well, let's look at people, let's look at people, let's look at critters that don't have middle ears. You've got four lizards here. Look at the little yellow spot on the lizard closest to you. That's its tympanum. That's the origin of its hearing organ. Lizards don't hear very well. They don't have middle ears. See, the middle ear is really, really a system. And it's a tightly comprised little system, elegantly designed. Here's why we've got middle ears in the first place. And some people might laugh at why we're even mentioning this, but check this out. The cochlea, inner ears, filled with fluid. It's got cerebrospinal fluid, paralymph. It's got endolymph in the scala media. It's filled with fluid. The cochlea is Greek for cochlea. Now, airborne sound, how the heck is that going to activate a fluid-filled cochlea? Think about it. If you have, if we're at a swimming pool and you put your head under the water, you dive into the pool and swim under the water. If I talk to you for a second from standing outside the pool, are you going to hear me? Of course not. 99.9% of the sound I utter is going to fly through the air, bounce off the water, and you're not going to hear a thing. This is what would happen if airborne sound was trying to stimulate a fluid-filled cochlea without a middle ear. The middle ear, oh, my dears, is interesting for us mammals. Now, this little critter has come for your hard drive, as you can see. It's a little lemur. It's a small little mammal, and mammals like mice and chinchillas and humans, we have middle ears. See, you might even think way back in evolution or the great designer who made us, mammals have middle ears so that we can hear a lot better. Maybe that's how animals got away from the terrible lizards called the dinosaurs. The dinosaurs couldn't hear a squat compared to what these little scuttling little critters could hear. The middle ear has a system of working. Let's take a peek at what it is. Let's look at the structures of the middle ear. You'll see this kind of pale green area, the middle ear, being a closed space and thus quite inaccessible to scrutiny from the outside. I always tell my classes that the middle ear is like government offices, closed unless forced open. That tube going down at the bottom right is the eustachian tube continuing down to the throat. Now when we swallow, we temporarily open up that eustachian tube so as to allow new air to come into that middle ear space. That middle ear space is lined with capillaries and it's always absorbing oxygen at a slow rate and when we swallow, we crack that eustachian tube open for just a wee second so that new air can get in there. Or if you blow your nose really hard, you can force air up into the middle ear. They tell you when you go up a mountain or fly in a plane to chew gum or swallow, again to equalize the air pressure. So the middle ear is a closed space and thus quite inaccessible to scrutiny from the outside. The function of the middle ear is really to increase the sound pressure so that airborne sound can activate a fluid-filled cochlea and it does this increase of sound pressure. It does this in three different ways. You can see on the screen here ones, twos and threes. Look at the ones first. Look at how big the eardrum is compared to the footplate of the scapes. Now that's the main way in which the middle ear increases the pressure of sound just for the heck of it. Take your hand, open your palm and put your left hand hard against your cheek. I can't see you do it so I don't know if you're doing it or not, but try. Push with your wrist against your hand against the cheek, against your cheek and push fairly hard. Now stop that. Now stop that. Now do it again with your fingertip. Push with the same amount of force against your cheek, but this time just with your fingertip. You can feel the definite difference. You've increased the pressure. Pressure is force over an area. Skinny bike tires have more air pressure than car tires. The main way in which the middle ear increases the pressure of sound is because airborne sound hitting that large drum, all that force is converged onto a small area. The workable area of the tympanic membrane or eardrum is 17 times larger than the area of the footplate of the stapes. So the TM is larger than the footplate of the stapes by roughly 17 to 1. Now look at number 2. You'll see the two main larger ossicles, the malleus and the incus. The malleus is of course attached to the back of the TM or eardrum and the incus is the second bone. Now look at the manubrium in the head of the malleus. Notice how it's just a little bit longer than the long process of the incus. Importantly now, look at the lines that connect the two number 2s. In other words, the line going straight horizontal from the head of the malleus to that little point, the short process of the incus to the right. Now you can think of that line as like the fulcrum upon which the teeter-totter or seesaw of those two bones works. Think of a teeter-totter or seesaw. Notice how when you give, when you're on a teeter-totter or seesaw with a child who's smaller than you are, you're going to give that child the longer end of the teeter-totter or the seesaw so that that child has the working advantage. And that's the same thing here. The manubrium and the head of the malleus are 1.3 times as long as the length of the incus. And so when these bones work together as a unit, sound pushing against the drum is activating the movement of the ossicles and the ossicles are twisting. Think of your two, put your two fists together, line them up so that your elbows stick about 45 degree angles from each other. Imagine one of your forearms being a little bit longer than the other one. And that's the issue here. That longer length of the malleus just makes, exerts a little bit more pressure against that incus. The pressure increase here is about 1.3 to 1 because the length of the malleus is 1.3 times longer than the length of the incus. And so you've got that little bit of a teeter-totter or seesaw edge that increase of pressure. The last thing is number three. I've pulled the eardrum toward the left here so you can see it sitting in the ear canal but notice the dotted or dashed lines. See how they indicate that the movement of the drum is not equal across the entire surface. It tends to bulge or bend a little bit more in the middle. Not at the umbil and not at the annulus areas that are indicated by the little round white circles. But mostly you can see the uneven ways in which it bends. That's called the buckling action of the tympanic membrane and that serves to increase the pressure by a factor of about 2 to 1. So now let's put the whole thing together. Look at the results in decibels. Anyone studying the decibels whether it's at IHS or whether at another place always will recall the decibel from hell. Let's look at it. What does this pressure increase of the ear of the middle ear? What does it result in in terms of decibels? Well look at the middle of the screen in terms of summary. Eardrum to stapes size that increases pressure by 17 to 1. The leverage action of the middle ear ossicles 1.3 to 1. The eardrum buckling action 2 to 1. Multiply these together and you've got a pressure increase of about 44 to 1. Now look at the bottom horizontal axis. Pressure increase. You know the interesting thing about the middle ear? It's phenomenal. The middle ear moves or I should say the eardrum moves about the width of a hydrogen atom when 0 dB SPL hits it. What's 0 dB SPL? That's the softest it takes for a normal hearing person to hear a 1000 Hz tone at 1 meter distance with two ears. Well that's softest pressure. That wiggles the drum by about the width of a hydrogen atom. We're talking small. And yet the middle ear can handle without much distortion pressures that are a million times as great as this. Now we can't sit there dealing in millions when we talk about sound pressure because we'd lose our mind among the decimals and the zeros. So that's why the decibel was invented. So if you look at a pressure increase, look at the horizontal axis. If you increase the pressure by a factor of 10 you've gone up 20 dB. The vertical axis is dB SPL. So if you've increased the pressure by 100 fold you've gone up 40 dB. So if you've taken a 0 dB SPL sound and increased the pressure by 100 times you're now at 40 dB SPL. And if you've increased the pressure by a factor of 1,000 times you've increased sound by 60 dB. And 10,000 you've increased it by 80 and so on. When you've made a pressure against the eardrum of a million times that of 0 dB SPL now you're up at 120 dB SPL. So really this whole system as you know is based on logarithms. That way we can deal with numbers between 0 and 120 instead of between 0 and a million. That's why the decibel works for us. So now when you look at the red lines on this picture here showing the 44 and 33 well look at a pressure increase of 10 corresponds to 20 dB SPL. A pressure increase of 100 corresponds to an increase of 40 dB. So look at 44 to 1. If the middle ear increases pressure by 44 to 1 that's somewhere between 10 and 100. That results in a total pressure increase of somewhere between 20 and 40 dB and yes it does. About 30 to 35 dB pressure increase is offered by the middle ear. So you know instead of making everything abstract there's an eloquent demonstration of this and all of us who've listened to tuning forks can do this for ourselves. Look at the Rene tuning fork test. If you have a tuning fork ding the tuning fork and put the stem of the tuning fork against the mastoid bone and you'll hear the tuning fork through bone conduction. So when you hear that then instantly pull the tuning fork away and hold the vibrating air conduction and you'll notice a distinct increase in the loudness of that tone. Once again ding the tuning fork hold it against your mastoid now pull it away and hold the tuning fork near your outer ear. You'll notice a drastic sound loudness increase and that increase is the increase offered by the middle ear. It's really quite an amazing structure the middle ear. Look at the resonances of the outer and middle ears. That aside but I think it's always interesting for us to know hey we are the curators and the custodians of the ear. It is we who need to have the story to tell. So I just I'm offering this just because we're on topic with things like this and think of this whole seminar this webinar as a way of just ingesting knowledge you may already have digesting what you've already got or ingesting look at the resonances of the outer ear on the top left you'll see this red increase of about 20 centimeters you can see that the outer ear canal and the concha those are offering about 20 db of a lift somewhere between 1500 hertz and 4000 hertz you're getting a big delight in every bite you're adding a little bit of juice there and that's important for hearing speech I mean that's for the high frequency the consonants of speech are softer than the vowels of speech vowels are loud and low consonants are like gentle dainty little china teacups easily masked by background noise and this outer ear if you think of the way your outer ear looks I mean it's such a weird looking thing why do we have ears looking like the way we do why are our ears having these weird creases in it and this shape like that with an ear canal that's about two and a half centimeters or about an inch in length that length of that ear canal and shape of the outer ear those give us the particular resonance offered by the middle ear or the outer ear and that resonance serves to amplify the high frequencies by about 20 db so you can really the outer ear is literally made for speech it's buried together and it's our ears are shaped the way they are because they have to be look at the right you'll see the top right you'll see the resonances or the transfer function of the middle ear and you can see where it is adding energy that's coming in or resonating so to speak now if you're adding those two things together, look at the bottom light green curve. That light green curve shows the loudness or intensity required for normal hearing humans to just barely hear all the various tones with one ear under a headphone. That curve is often called minimal audible pressure or MAP. And it is important to note that that curve is IS, underlined, bold, italics, however you want to do it, that curve is 0 dB HL on the audiogram. So, which is why we get our audiograms, our audiometers calibrated every year to make sure they're spitting out those particular different decibels across all the frequency range. So, to make a long story short, our outer ear canal and the resonance of the outer ear plus the middle ear, those two things together give us that light green curve below, the sweet spot. They enable our greatest hearing sensitivity to occur between 1,000 and 4,000 Hz, which is the home of the high frequency consonants of speech. And you can see that curve, meaning that it's ducking down near 1,000 and 2,000 Hz especially, although we're almost down to zero. And that's minimal audible pressure created by the resonances of the outer and the middle ears. We can and should move on from here, looking at the middle ear being a closed space. It is a closed space, and yet tympanometry enables examination of a closed middle ear space from an outer ear canal. This is the cool thing about tympanometry. Without ever going into the middle ear space, just by changing air pressure in the outer ear canal, we can check out the function of what's taking place behind the drum. It's the most fascinating procedure we have in our pure tone battery. So, let's look at what it involves. Tympanometry involves impedance. What's impedance? Impedance is the opposition offered to the passage of sound. The middle ear is a structure, and so it too is going to carry sound through it. All structures carry sound through, but they also impede sound. Nothing comes in this life for free. Things are pushed through, and there's always some impedance. Well, the middle ear impedance is comprised of three things. The opposition due to its mass, the opposition due to its stiffness, and the resistance it offers to sound passing through. Think of mass first. Mass resonates with low frequencies. Think of, to get this through, you're sitting down in your apartment and the people upstairs above you are playing the stereo loudly. What's coming through your ceiling? The bass guitar and the drums. Why? Because your ceiling is mainly dominated by mass, and mass resonates with lows. So, lows are going to get through. Think of it another way. You're standing in front of a locomotive. Do you think you're going to be able to grab that locomotive and jiggle, wiggle, wiggle it and move it back and forth quickly? No. You're going to be pushing with about 200 people to make it move one way and then pulling slowly with 200 people trying to stop it and pull it and move it the other way again. Mass resonates with low frequencies. The opposite is true for stiffness. Stiffness, if you think of it as hard, thick springs sticking out of a wall, you're going to run into a lot of opposition if you grab that spring with both hands and try to push it slowly and pull it slowly. But if you stand with both feet on the ground and you grab that thing with both hands and move it back and forth quickly, you're going to notice a lot less opposition. Stiffness resonates with highs. The middle ear is a stiffness-dominated system. The ossicles are tiny, so it doesn't have much mass. They don't contribute much mass at all. They're the smallest bones in the body, and the stapedius is the smallest of the three bones. The middle ear is dominated by stiffness. The ear drum is tight as a drum. The middle ear ossicles are all connected tightly to each other and to the back of the drum, and the load of fluid in the cochlea, that's creating a whole stiffness of that entire middle ear system that precedes it. The resistance of the middle ear, resistance in any object is like simple friction, and it's equal for all frequencies in any sound passing through. The best resistors, I can think, are any dampened peaks in a frequency response. Resistors dampen or reduce frequencies anywhere that peaks may be. Well, the resistance of the middle ear is offered by its ligaments, and the ligaments of the ossicles are tiny and offer little resistance. So let's move on to some terms encountered in tympanometry. What we're doing here is just laying down some foundation. We're almost there so that we can start talking about tympanograms, but these are key concepts to keep in mind before we go there. There's terms encountered in tympanometry. One of them is called impedance, which we've discussed, and the two words often given are reactance and resistance. Reactance is the opposition due to something's mass and the opposition to passage of sound due to something's stiffness. We've discussed those already, and those two terms together are often called reactance. Resistance, as we said, is like simple friction independent of frequency. But let's flip impedance around. Let's talk about what the ear passes through instead of what it impedes or blocks. And if you take impedance and you flip it right side over, a frown is an upside-down smile. What the ear passes through is called its admittance. That's the inverse of impedance. In the middle ear, this is mostly the compliance of the ear. And what is compliance? Well, compliance is the inverse of stiffness. Remember we said the middle ear is a stiffness-dominated system? Well, if you talk about what the middle ear passes through, we're going to talk about the opposite then of its stiffness, a compliance system. So tympanometry is testing the middle ear's compliance, what it passes through. Immittance is a generic term to encompass all of the above. But to quickly summarize again, all objects offer impedance to the passage of sound. Admittance is just the flip side of impedance. Back to impedance again, the stiffness is the main component of impedance. When we've been talking about the middle ear, so to flip stiffness upside down and talk about what the middle ear passes, we're going to be speaking mostly of its compliance. So these concepts regarding the middle ear have to be kept close to our hearts. There you go. Key concept behind tympanometry. For the middle ear to be most efficient, the air pressure has got to be even on both sides of the tympanic membrane. Look at the outer ear canal. The air pressure there has to be equal to the air pressure in the green area called the middle ear. In that way, the middle ear, although it's a stiff system, it will be least stiff. The middle ear, although it offers compliance, it's admittance. Well, the middle ear is most compliant when air pressure is even-steven on both sides of that drum. It's always stiff, but it's least stiff when the air pressure is even on both sides. Tympanometry is really a test of this middle ear efficiency. We're checking to find out when the air pressure is even on both sides. It's really a test of this middle ear efficiency. We're checking to find out when the middle ear offers the least impedance and when it offers the least stiffness. Conversely, we're trying to find out when the middle ear is offering most admittance or when it is most compliant. So what we've got in tympanometry is a three-holed probe, a probe with three holes. Air pressure has got to remain sealed. When that probe is stuck into the ear canal, it's got to be able to make sure that there's a tight seal and that no air can escape. You've got three holes. One's a speaker. Some people call it a receiver. That, to me, is always confusing, even in hearing aids. A receiver is a speaker. I think engineers call it a receiver because it receives all the electrical current. But in practical terms, a receiver is a speaker. Another probe hole on the bottom is the microphone. And it's measuring whatever's being picked up. And the third hole is an air pressure changer. It allows for changes in air pressure. So the speaker emits the tone. Look at the arrows heading toward the eardrum. And whatever bounces back off the eardrum is picked up by the mic. And what we're doing is we're keeping the tone constant, and we're changing the air pressure in that outer ear canal. And we're finding out, is there any changes in the amount of sound bouncing back as a result of changing the air pressure? Let's see. With greatest middle ear compliance, the middle ear is the least stiff, and it offers the least overall impedance. This means more sound will be able to go through and less sound will be impeded by it. And tympanometry measures exactly this. How it is done. Low frequency tone is used. It's a 226 hertz tone. Why is it a low frequency tone? Because the middle ear is a stiffness-dominated system. It's not going to naturally like to pass a low frequency tone through it, remember? Mass resonates with lows. But the middle ear is a stiffness-dominated system. We deliberately use a low frequency tone in tympanometry because we want that sound bouncing back. If too much of it went through, we wouldn't have anything to measure. So we always want sound bouncing off the drum so that we've got something to measure. That's why we use a low frequency tone. It's because the middle ear is a stiffness-dominated system, which would naturally want to pass a higher frequency. Now, why is it 226 hertz? Why not 250? Why not 225? Well, that's done for reasons of calibration. And I'll tell you something, I don't even want to go there this time. I mean, blah, blah, blah, whatever. It's a calibration issue. Suffice to say, it's a low frequency tone. And the intensity of the tone is about 70 dB SPL. That's what comes out of the speaker. And that will normally bounce off a stiff middle ear system. It's supposed to. That's what you want. Otherwise, you've got nothing to measure, laddie. Alrighty then. Now, tympanometry is determining external auditory meatus air pressure where the greatest middle ear efficiency occurs. Well, look at this weird-looking graph with a green-looking V in it. The decibel SPL of a tone at the probe mic is measured while air pressure changes from positive to negative. If we look at this slide again, I'm going back a slide here, look at the air pressure changes. What tympanometry does first is it adds positive air pressure to that outer ear canal. When you're adding positive air pressure to that outer ear canal, look at the horizontal axis now on this graph. You'll see positive. When the air pressure is positive in the outer ear canal, now the air pressure behind the drum is at room air pressure. So you've made the air pressures uneven on purpose. Positive air pressure in the ear canal, regular room air pressure in the middle ear space. So you've made that stiff middle ear system even more stiff. You've made it really stiff. Because you've done that, the middle ear is not prone to pass much of that sound through. In fact, look at the vertical axis where you'll see less and on the top, lots. The vertical axis reads in amount of dB SPL bouncing back off the drum. So as you change the air pressure from positive to zero, meaning regular room air pressure, to negative air pressure in that ear canal, what effect does that have on the amount of dB SPLs of the sound bouncing back? Well, at positive air pressure in the ear canal, you have whoppingly uneven air pressures on both sides of the drum. So lots of the sound will bounce back. As you move, make the air pressure like room air pressure. We'll just call that zero. At room air pressure, now the air pressure on both sides of the drum is even. And then less of the dB SPL is bouncing back. Some of it is actually going through. And now when you continue to make the air pressure negative, toward negative now, you're once again making the air pressures uneven on both sides of the drum. And because of that, what's happening is you've got more and more sound bouncing back off the drum. Some of you might be going, well, this doesn't look like a tympanogram. They look more like tenths. Well, let's check it out. A funny thing about tympanometry is that while we actually measure dB SPL picked up by the drum, we do this in order to quantify something else on the y-axis, namely compliance. So we're talking, why are we doing this? Why is the vertical axis not simply called dB SPL that bounces back off the drum, like in this picture? Well, the answer is it used to be. When tympanometry was just being developed, that's the way they drew a tympanogram. There's a reason we don't do that, though. We now call the vertical axis compliance instead of amount of dB SPL bouncing back. Look at the blue letters here. How come? Why is the vertical axis not simply called dB SPL that bounces back off the drum? The big reason is this one. There would be so much variation among people in the amount of SPL bouncing back as you changed air pressure. This is because people have different sizes of ear canals, different properties of ear canals. Look at all these 4Vs. You could just surmise maybe these were taken from four different people who had normal middle ears. You'd have so much variation. There's a second reason, so I would write this down. There's a second reason why we call the vertical axis compliance. It's because that's actually what we're interested in. We're interested in examining the physical property of the middle ear itself. We're clinicians. We want to understand is the middle ear abnormally stiff or not. So let's talk about what we want to talk about, namely the middle ear's compliance. So for these two reasons, variation among people plus the fact that we really want to address the physical property of the middle ear, namely its compliance. Now the tympanogram is drawn much like a pop tent. Same issue, same kind of shape. It's just inverted. We're putting a probe in, positive air pressure on the lower right ear, and what's happening here is most of the sound is bouncing back off of the drum because you've made that ear really stiff. But we say now that it has low compliance. Look at the vertical axis reading compliance. Most sound is bouncing back at positive air pressure, so you have very little compliance. You've got a lot of stiffness. As we move the air pressure to zero, now the air pressure is even-steven on both sides of the drum. Now less sound is bouncing back, more sound is getting through, and we say you have high compliance. As we continue to change the air pressure to negative, you've made the air pressures uneven on both sides of the drum. You've now stiffened that stiff system even more, so you have low compliance. More compliance means less stiffness. The middle ear is a stiffness-dominated system, but we're looking at its compliance. The units of measurement, the horizontal x-axis reads in air pressure. It's measured in units of decapascals or millimeters of water. These units are essentially equal in value. The vertical axis reads in terms of compliance. It's measured in units of milliliters or cubic centimeters. That's kind of a strange thing, though, because they are essentially equal in value, but they're not very intuitive in terms of reading stiffness or compliance. What we do is we'll say the milliliters or cc's of air do not intuitively convey compliance, so we use a unit based on opposition or resistance. You'll remember how the ohm is an electrical measure of resistance. Well, if compliance is the inverse of stiffness, and stiffness is what's offering most of its opposition, okay, we'll look at the ohm. But we're measuring compliance, which is the inverse of stiffness, so we flip it around to read mo, M-H-O. The ear is small, however, so mo, being as a unit, is too large, so we use thousands of a mo, millimholes, M-M-H-O's, to indicate units of compliance. The normal tympanogram is shaped like a tent. When the middle ear is most efficient, air pressure is equal on both sides of that eardrum. When least probed tone SPL is picked up by the probe mic, most is getting through. At this peak, the air pressure behind the TM must, therefore, be the same as that in the outer ear canal. Look at this picture carefully. The bottom of the tent, most SPL is picked up by the probe mic, the tails of the tent, that is. The peak of the pup tent, least SPL is picked up by the probe mic. In fact, you can listen to this. When you're getting tympanometry done on yourself, you're going to hear the tone starting at positive air pressure, being very soft, and you'll hear it get louder, as the air pressure changes to zero, and then to minus 200 decapascals. Tympanogram types. Look at this slide showing progression, stages of otitis media. Type A, being a normal tympanogram, the peak is over room air pressure. Type C indicates early otitis media with negative middle ear pressure. Now look at here, the type C, the peak is over negative. That means you were able to get highest middle ear compliance, least middle ear stiffness, when you made the air pressure in the ear canal negative. That means the air pressure behind the drum must also be negative, because now you've made the air pressure even-steven on both sides of the drum, but to do that, you've had to make the air pressure in the ear canal negative. If your peak is over negative air pressure, it means that the air pressure behind the drum is also negative. Now, that's early otitis media that occurs because the eardrum is sucked back. You're getting a vacuum in the middle ear space. Remember we said earlier, the middle ear space is lined with capillaries. They're always absorbing oxygen. Sore throat, swollen mustache and tubes, when you swallow, no new air gets up in there. So you're getting a vacuum in the middle ear space. You'll get a type C tympanogram, peak over negative air pressure. If you leave that untreated, now the middle ear space fills with fluid, serous otitis media, uninfectious, and then it gets pus-filled, infectious, turning to separative or purulent otitis media. Then your type C tympanogram will start looking like a type B. So if you look at now the third one down, type C turning into a type B, now your peak is starting to disappear because the middle ear is filling up with fluid. When your middle ear is filled with fluid now, as that process continues, you're getting a type B. And a type B indicates no peak at all. Air pressure can't compete with fluid. So when you've got a type B flat tympanogram, you know you've got advanced otitis media with fluid. You know how long tympanometry takes to do? Five minutes. It's astounding to me how few people use it, and it should be used. Not for state funding or God knows what. It's for you as a clinician to get a grip of your own test and to back up a finding. Hey, your teachers told you in high school, two dots makes a line. Well, an air bone gap is one dot. This is another dot. Now you've got a story to tell. Enough on that tab. Move to the next slide. There's lots of complicated explanations about static compliance. And static compliance also addresses types of tympanogram. People come up with all these weird definitions, and they're quite true, but they're so scientific. I don't know. I look at it as it's basically the height of your tympanogram. How tall is your pup tent? Some people have abnormally squat pup tents. Now we've already said we're using compliance on the vertical axis so that everybody's tympanogram will be roughly the same size, but I mean roughly still. So normal static compliance is a relatively normally tall tympanogram. Various pathologies, however, affect static compliance. One type is otosclerosis, a tympanogram with unusually small static compliance. That's going to be called a type AS. Now importantly, notice how first it's squatter than normal. Note also how the peak is still over zero, so there's no problem with air pressure behind the drum. Air pressure isn't the issue. The pressure behind the eardrum being uneven with that of the ear canal, room air pressure in the ear canal, that's not the issue. That was more of an issue with otitis media. But now, if your peak is still over zero, but your tympanogram is abnormally squat, that's called a type AS tympanogram, type A, but stiff, consistent with otosclerosis. Now otosclerosis is a pathology. It's kind of a silly name. Sclerosis means hardening, and actually otosclerosis is a soft, porous growth of bone around the footplate of the stapes. But it's a hereditary pathology, more common in Caucasians, more common in women, especially during pregnancy, hits in young adulthood, and treatments often are stapedectomy or wearing hearing aids. Anyway, the point here is otosclerosis stiffens the middle ear system more than it should normally be. As a result, you will get a type A tympanogram, but you will not get very much compliance. It is overly stiff because of the pathology affecting the footplate of the stapes. Moving on to a type AD, you might look at the top here, you'll notice a type AD tympanogram is off the chart. You can't even find the peak. It's a stovepipe. A type A is shown there as normal, but a type AD is an overly tall pup tent or tympanogram, and it's consistent with disarticulated ossicles or a monomeric eardrum. Now, disarticulated ossicles means ossicles that are no longer stuck together as they should be. So your whole middle ear system is abnormally flaccid or compliant. It's not at its usual stiffness. A monomeric TM is mono means one that's a single layer of tissue comprising someone's eardrum or parts of it. So that might be caused by repeated middle ear pathology. A monomeric TM also results in an abnormally flaccid or overly compliant middle ear system, a type AD for disarticulating. So these are your tympanogram types. We've gone over otitis media, early otitis media, advanced otitis media, static compliance now being another issue, and we've addressed two more pathologies, otosclerosis or other middle ear pathologies, disarticulated ossicles or a monomeric eardrum. So there's five different pathologies looked at right then and there. But tympanometry is a rapid way of discovering things. The last test that's done quite automatically by tympanographic equipment is physical volume of the ear canal. Now look at the left picture here. Normally a closed ear canal, see the probe tip stuck in the left side of it and you can see the ear canal there, sort of a grayish area. The normal physical volume of air trapped between a probe or a hearing aid for that matter and an eardrum is about one to one and a half cubic centimeters. Now in Canada we do metrics. So centimeters, about two and a half of them fit into an inch, okay? Basically a 2cc coupler overestimates the physical volume of a closed ear canal space. A closed ear canal space doesn't normally have two cubic centimeters. It's a little bit less than that. So 2cc coupler readings on ANSI measurements, those always underestimate the sound pressure that's really taking place from a hearing aid. When you take a hearing aid and stick it in someone's ear, there's less distance between the end of the hearing aid and the eardrum and so your sound pressure in a smaller area is going to be more. Now this is a talk on tympanometry, but let's look here for the same type of concept. A closed ear canal space is one to one and a half cubic centimeters. So if you have a true, look at the black sentence, the second black sentence, a true type B tympanogram, if you get that and you see a normal physical volume, you really do have a type B. But if you have a, look at the blue line just above it. If you have a type B tympanogram and you have an overly large physical volume, look at the right graphic below. You're going to see a hole in the drum. Now the probe is measuring the air not only in the outer ear canal, but also continuous with the air in the middle ear space. So you're going to have an abnormally large physical volume. If you have a hole in your drum, you won't be able to get a tympanogram and you will have a type B tympanogram with an overly large physical volume. Can you see how we fit the tests together like a sleuth? You've got to use your cues and you'll find out what's going on. If you're getting a type B tympanogram with no peak and you have an abnormally tiny physical volume, then your probe tip is probably jammed against the outer ear canal. Do your tymp over again. Now I'm going to finish. I've got a minute left to go here, but acoustic reflexes, I'm just going to announce this to you. Just something, we're not talking about it today, but it is also part of tympanometry. The acoustic reflexes involve inner hair cells. Look at the top hair cells there. They're like the American side of the falls. Not with the horseshoe or V-shaped, they're like the Canadian side of the Niagara Falls, I always say. At any rate, inner hair cells send all sound info to the brain. Without them, you're deaf as a post, but they have a fundamental flaw. They cannot pick up sounds below conversational speech. The outer hair cells are needed to do this. The cochlea is not a one-way street. Inner hair cells send info to the brain and outer hair cells pick up sound from the brain or from other parts of the workings of the cochlea to help the inner hair cells pick up softer sounds than conversational speech. The acoustic reflexes involve a whole arc or loop. Sound from the outer to the middle ear to the inner hair cells to the eighth cranial nerve to the brain stem and then a message is sent back down the fifth cranial nerve, back down the seventh cranial nerve to the tensor tympani muscles and to the stapedius muscles respectively. Those muscles are tightening the middle ear system, making it more stiff. The acoustic reflexes occur with loud sounds. They will also affect your tympanogram, so without air pressure, just by changing sounds and making them loud, you can cause a change in the compliance of the middle ear as well. That's why acoustic reflexes are part of tympanometry, but I mention this here. Look closely. Look, for example, two people with the same sensory neural loss. If one has excellent or good speech discrimination and the other one has poor speech discrimination, chances are the person with the better speech discrimination will have acoustic reflexes at reduced sensation levels. The person with poor speech discrimination will probably have absent acoustic reflexes. This is especially the comparison to make if it's mild to moderate or moderate sensory neural loss. Beyond moderate, when you start getting a severe sensory neural loss, you shouldn't have acoustic reflexes anyway. But this is a food fodder for a different prep for another webinar, and it's a fascinating topic of conversation, which I'd love to have with you on a future date. I'm going to stop here because my talk is done. I would be happy, however, to address anyone who has questions. Thank you very much. Thank you, Ted. We're so excited that we had over 270 of your fellow colleagues joining us today on the webinar. We do have a little bit of time for questions, so if you have a question, please enter it in the question box on your webinar dashboard. Our first question comes from Jennifer in Ontario. She wants to know, if tympanometry is measuring the amount of dB SPL bouncing off the eardrum, then why does the vertical axis not simply read that? You know, Jennifer, I think that's a fascinating question, and it always bugged me as an audiologist because, frankly, and I know your name isn't Frank, but to be perfectly honest, I didn't know the answer to that question either, and I'll wager to say there's a lot of practicing clinicians that don't know the answer to that either. The reason why we don't is because there's two reasons why. One reason is because if we actually measured SPL bouncing off the drum as we changed air pressure, you'd have so much variation amongst the sizes of resulting tympanograms among people. People have different sizes and shapes of ear canals, which is really going to change or it's going to affect the dB SPL bouncing back as a result of changes in air pressure. So you'd have tympanograms, some would be tiny, some would be large. So when we choose to measure the middle ear function in terms of its compliance, we are also addressing its physical status because that's really, as clinicians, what we are interested in is the physical status of the middle ear. So for two reasons, we use the vertical axis in terms of compliance. One is when we do that, it really reduces the variability among normal tympanograms and among normal individuals. Secondly, it really addresses the physical properties of the middle ear in which we are interested. That's why, even though we are using SPL bouncing back off the drum, we are using it as a tool whereby to assess the middle ear's compliance. Thanks for that question, though. It's a good one. Very helpful. Thanks. Our next question is from Anjan in California. He would like to know how much reduction in SPL is accomplished by the stapedius muscle and what is the lowest activation level for this muscle? That's a great question, too. We're ahead of the game in acknowledging that the acoustic reflex is mostly about the stapedius muscle and not so much about the tensor tympani, in humans anyway. How much does it reduce? Well, some research says by around 5 dB. Some research says by about 15 dB. I guess I would go for a medium of about 10. The middle ear, when the acoustic reflex kicks in, it might reduce the SPL going through the middle ear, transferring across the middle ear by about 10 dB. It's in interest, too, the acoustic reflex is strongest for low-frequency sounds. So when you put a loud, low-frequency sound in, the acoustic reflex muscles tighten, and when they tighten, they artificially stiffen the middle ear more than it already normally is. That, temporarily, increases its impedance for the split second that the loud sound is present. And so you've reduced its compliance. And so more sound will bounce back to the probe again. The purpose of the acoustic reflex is actually not so much to reduce the chances of noise-induced hearing loss, as many people think. If you think of the frequencies that cause the strongest acoustic reflexes, those are the low frequencies. And when you think of your voice, one of the loudest parts of your own voice, lows. And when others hear you, you hear them at about 65 dB SPL. When you speak, you hear yourself at around 80, 85. And that's the level that the acoustic reflex tends to kick in, around 80, 85. The acoustic reflex is really designed to reduce the loudness of your own voice while you talk, and it reduces the upward spread of masking. So you can better hear high frequencies when you talk. Weird, eh? There's my Canadianism. Eh? Thank you. Thanks, Ted. Our next question is from Sam, and we've had a couple different questions like this. What is the acceptable level of Cerumen to still have confidence in temp testing? What's the acceptable level in Cerumen? Yes. Ah, you know, if you can be careful with that one. If you're looking in the ear canal and you see a bunch of gunky old Cerumen, it's time to do some Cerumen management, because the Cerumen is going to more than likely plug up one of your, at least one of your probed holes. However, if the Cerumen is kind of, you know, too many people use Q-tips, and they tend to push Cerumen into the bony portion of the ear canal, and if you can still see the drum over a little hump or a mound of Cerumen that's laying there in the middle, in the outer ear canal, I would try tympanometry then. You can, as long as it's not plugging your probe, as long as it's not lateral or outside or to the edge of your ear canal enough to do that, because you've got to push your probe into the ear canal. But if the Cerumen is fairly medial, like fairly inside the ear canal, and you can still see the drum behind it or through it sort of, you know, like over it, go for it. Great. We have one final question from Tom in Arizona. He wants to know, why are so many terms used in tympanometry, such as impedance, compliance, emittance, et cetera? You know, that's a great question, and it addresses how impedance or tympanometry evolved. Remember, it first evolved as a way, Swiss Lockheed and Turkildsen and these people, Nets, they were all playing around with tympanometry way back in the 50s when it was being first investigated. By the way, the decade of tympanometry is the 70s. That's really when it came into clinical practice, but to get to your question, first they were measuring amount of SPL bouncing back off the drum as you changed air pressure, and then they called it impedance testing, because really, you're testing the impedance of the ear, checking when most sound bounced back. As equipment evolved, the questions began to change, and we thought, well, let's really address compliance. Let's find a unit for compliance, and really, we know the middle ear is mostly stiffness dominated, so when we talk in terms of its impedance or its emittance, its emittance, the big camel is really compliance. The two little mice that accompany that camel are called resistance and opposition due to mass. So the big thing is opposition due to stiffness, or flip it over, the biggest part of impedance for the middle ear, it's almost 95% compliance. So you've got these terms bandied about, but really when you hone in on it, it's tympanometry, you are checking the compliance of the middle ear system, and you are using air pressure to change things, and really you are measuring the SPL bouncing back as you are changing the air pressure. Some people got tired of all the terms, and they just used emittance testing. I've heard that one as well. You're going to run into compliance, you're going to run into tympanometry, you're going to run into emittance. They're all, for practical clinical purposes, synonyms. Thanks for your question, though. Well, thank you, Ted, for an excellent presentation, and thank you, everyone, for joining us today on the IHS webinar, Tympanometry, Why It Should Be Used by the Hearing Instrument Dispenser. If you'd like to get in contact with Ted, you may email him directly at tvenema at conestoga c.on.ca. For more information about receiving a continuing education credit for this webinar, visit the IHS website at ihsinfo.org. Click on the webinar banner or find more information on the webinar tab under professional development. IHS members receive a substantial discount on CE credits, so if you're not already an IHS member, you will find more information at ihsinfo.org. Please keep an eye out for the feedback survey you'll receive tomorrow via email. We ask that you take a moment to answer a few brief questions about the quality of today's presentation. Thank you so much, and we'll see you on the next IHS webinar.

Dr. Ted Venema

Conestoga College

tympanometry

middle ear

hearing loss

otitis media

otosclerosis

acoustic reflexes

stapedius muscle

cerumen