Lec #1 Hearing Disorders: Part 3 PDF

Created with Coconote - https://coconote.app Lec # 1 Hearing Disorders: Part 3 Okay. So we have about 30 minutes left, if not. So MRI scans is complementary to CT scans, but it's really good for soft tissue anatomy. MRI stands for magnetic resonance imaging. The other thing to note is MRIs, there'...

Created with Coconote - https://coconote.app Lec # 1 Hearing Disorders: Part 3 Okay. So we have about 30 minutes left, if not. So MRI scans is complementary to CT scans, but it's really good for soft tissue anatomy. MRI stands for magnetic resonance imaging. The other thing to note is MRIs, there's no radiation involved. CT scans, they're the new CT scanners are actually quite good. There's minimal radiation. So but MRI is actually safer because there's no radiation involved. But if you wanna look at the brain, brain stem, cranial nerves, it's the best sort of imaging modality we have. Again, look at remember that when we looked at the brain on the CT scan, it was just gray. Right? Look at the MRI here. You can see the gyri, like, white matter. You can see the cerebellum. Right? The details are very, very different. So this is actually showing you the inner ear. You can see the lateral semicircular canal, the sort of the inside of the the membranous part of the semicircular canal, not the voleaning part. Right? So it gives you well, it's the same anatomy, but gives you different perspective. And this is showing you that's the brain and brain stem. The inner ear the cochlea is here. Right? The basal turn, apical turn, lateral canal. And these are the nerves. Pineal nerve number 7 and 8. Right? Again, this is actually showing you the nerve structure. On the CT scan, we saw the bony canal where the nerves are running, but you can see the actual nerves on the MRI. So for MRI, we can find things like these are 2 small brainstem lesions called acoustic pneumomas or vestibular spondylomas. It's that sort of relatively common tumor benign tumor, so it's not cancer, but it's a benign growth or tumor that arises from your 8th cranial nerve. Right? So we're gonna talk about this entity later, but how do we diagnose it? Well, we have to do an MRI, and then we can see it. Right? We can see something lighting up here that's not there. Little sausage like lesion on that side. This is showing you a bleed. It's the same image but different windows. But this is someone who had a bleed stroke, right, into their brain stem, which may affect hearing as well. Okay. So the final bit today is hearing assessments. Okay? So mainly we're gonna talk about audiograms. But for you speech people, you should have your hearing checked by one of your colleagues in audiology just so they can get practice, and also you can appreciate how a hearing test is done. And sometimes it can be a bit intimidating, especially for you guys in speech, but we just have to know the very basics of audiogram. Right? Because disorders will have different type of audiogram, which can point us towards a diagnosis. So decibel is a sound pressure unit. It measures intensity. How loud is the sound, basically? Now the important thing to note is that it's on a logarithmic scale. Right? Again, not everyone has a math background. Logarithmic means it's sort of it changes exponentially. Right? It's not it's not a linear scale. Right? It doesn't go up on a linear fashion. So it may go up like this for instance. That's logarithmic scale. So it's not linear. The other thing to note is it's not a relative measure, And we'll explain that in a bit. So it's not linear, meaning that if you double the vestibial vestibial hearing level, it doesn't mean you're doubling the sound. Right? Because it's not a linear scale. So be aware of that. Right? So you may think, well, few to few decibel worsening of a hearing loss, you may think, well, not a big deal, but it could be a big deal depending on where on that scale you are. Right? So when we talk about decibel hearing level, we're talking about DVHL, that's the hearing level, that's the most sort of commonly described audio variant result. And that's based on again, it's a relative scale. It's based on lots of data gathered from normal hearing individuals. So 0 decibel doesn't mean that there's no sound. Because 0 decibel, probably like dogs can hear it, for instance. It's just normal human beings who are on the cusp of hearing it. So it's a relative scale. So 0 decibel hearing level really means that it's the minimal intensity for an average normal hearing ear to perceive a specific frequency of sound. Okay? So if you're sitting in a booth and you're trying to hear 0 decibels, you may hear little, like, beep, clumps in the line. Right? It's not like it's loud all the time. Because again, that's sort of the minimal level that you can say and hear it, like, 50% of the time. K? So 0 with s bell, this means there's no sound. There's just this level of minimal detectable sound. And that's the reference used in most audiometers. Now there's this other thing called sensation level, and we've been talking about hearing level. Sensation level, and it's a bit esoteric, maybe a bit confusing initially, but it's just a relative to your own hearing level. K? And you'll see where this becomes important, but sensation level is a game that's a relative, it's based on your own or individual's hearing threshold. An example an example is listed there. And we'll talk about exam we'll talk about why we need to know sensation level, but mostly it's the hearing level that's what we consider when we talk about hearing tasks. Okay. So there are 3 parts of an audiogram. So here's, let's say, a very generic looking audiogram result page. So obviously name, date, who's doing the testing. So most people think about this part, the pure tone testing. Okay? Pure tone audiograms. But there are 2 other parts to the audiogram. Right? 2nd part is called the speech testing, speech audiometry, which is shown here. And then the last part is emittance testing or acoustic impedance testing. K? And we'll talk about all three parts. But, basically, there are 3 parts of the audio audiogram, and they all should sort of match the results or agree the results should agree with each other. Because if one shows really bad here and not but the other one doesn't show it, then there's something going on. Okay. So pure tone testing, this is what most people think about when we talk about hearing tests. Right? So this is where the sound stimulus is the pure tones at single frequencies, usually at these octave frequencies. Like, 255 100 hertz and so on. And we do air conduction as well as bone conduction. So there are again, there's right side, left side, there's mass, unmasked, and there are different symbols, and you don't have to know the symbols. I just want you to know that there are different symbols. So if you see, like, triangle or circle or x, they just mean different different things, like maybe the right ear, left ear, masked and masked, and we'll talk about what masked ear is. That's for air conduction. Bone conduction has a different symbol that they use, and it's more like, like, greater or lesser, bigger, and different colors denote different sides. But again, you don't have to memorize this. Just want you to know that when you see different symbols that means different ear and air conduction versus bone conduction or mass drum. So when you do pure tone testing, the way it's done for air conduction is usually through a headphone or insert earphones. Right? It's like the Renee air conduction testing. It's testing the entire auditory pathway from the outer ear, external ear to the inner ear. So it's usually done with a headphone or earphones. And again, you're sitting audiologist will generate the sound stimulus at the specific frequencies at different intensities. It'll be they're literally they're like beeps. Right? They're go beep beep beep. Right? And you say, basically, yeah, I hear it I hear it on my left side, right side, and then you know you know where to check off on that figure. Now again, some of the sounds may be subtle or you may not be paying attention, so it's not like you have to get it right all the time. It's about 50%. Right? Especially in the sort of the not as intense sort of sound pressure levels. Now for bone conduction, you use this device. It's a bone oscillator. Right? Again, it's like Renee testing when you blow the mastoid. So it's a literally device that goes on your mastoid bone, and it produces vibratory energy. Right? It's not actually sound that's coming out, like air conduction, it's actually vibratory energy that's transmitted to the inner ear. So what that's doing is it's actually bypassing the external ear. So that's why it's bone conduction. It's just literally conducting sound energy through bone. But again, the same thing, lowest level, decibel hearing level, where the person perceives about 50% of the sounds stimulus. Now usually, bone conduction is not tested at the super high frequencies, like 4000, 8000, because the vibratory energy is so high that you can actually hear it rather than feel it. So that's why it's not always tested. So again, that part that air conduction tests different part of the auditory pathway than bone conduction. So from that, you can get what we call PTA or pure tone average. So that's literally adding up the decibel hearing levels at the 3 frequencies, 500, 1,000 and 2,000 hertz, and then dividing it by 3. Those are important frequencies because that's where most sort of communication happens. Average. So that should be PTA should be within 10 decibel hearing level of speech reception threshold. So what's speech reception threshold? Well, it is the lowest level decibel hearing level that a person can repeat a spondee of 50%. So we've done the pure tones now. Right? You get the beep beep beep. So that's the sound stimulus. Now we're moving on to speech audiometry. No pure tones. So the sound stimulus is actually words. Okay? And spondee anybody know what a spondee is? So it's bisyllabic words with equal emphasis on the syllable. So, like, baseball, hot dog. Right? Very simple words that you can repeat back to the audiologist. So these are, again, sounds they're speech stimulus, not pure tone beats. And then you have to sort of repeat what you said or what the audiologist at a different frequency, different sound intensity might have. So again, speech reception threshold, you the result you get is, again, decibel hearing level. Right? Meaning, the audiologist will produce those spondee words at different frequency, at different intensity, and then you get it right 50% of the time. So it's very similar to pure tone audiogram, except the sound stimulus is those words. Now speech, that's why it has to be similar to PTA, pure tone average. Right? Which makes sense. Now the next speech audio speech testing is called speech discrimination scores. So we use phonemes for these. K? So phonemes are monosyllabic words, like, all, hat, dog. K? So this, there's, like, a prescribed list. So let's say you say 10 phoneme words at about 20 to 40, that's called sensation level above SRT. So you say 10 you say 10 words, and then the person says 7 out of 10, and then the So this is where sensation level comes in. Right? So if you do pure tones and you find somebody that has moderate hearing loss, there's no point of producing the sound stimulus for speech audiometry at, you know, 10 decibels. They're not gonna hear it. Right? So you have to sort of consider their own hearing levels and readjust your sound stimulus level. Right? So it's based on the person's sort of threshold levels. Right? So that's sensation level. Okay? So again, they're pure tones, and then there's speech audiometry, speech reception threshold, and speech discrimination scores. Right? So, I mean, those are the first two parts of the speech op or audio frame. Now from those results, you can get what we call an air bone gap. So normally, you want the air conduction to match bone conduction. However, if there is a gap, if there's a difference, then we call that an air bone gap. So that means you have what we call conductive air loss. So there is a difference between bone conduction and air conduction. And the maximum level is about 60 less than long hearing loss. Now sensory neural hearing loss is when you have abnormal air conduction with no air bone gap. So again, there are 2 major types of hearing loss. Right? Conductive hearing loss, where the sound energy is being blocked. Sensory neural hearing loss, where there's something going on with the inner ear or even the outer brain nerve. You can have both. Yeah? Sorry. What was a, b, g? Air bone gap. Yeah. So that means you have conductive hearing loss. Right? But you can have both, sensory neural and conductive hearing loss, and we're gonna talk about many conditions that can have mixed hearing loss, or you can have both. Now other things you may find on an audio brand, there's one thing called recruitment. Recruitment is when you have increasing signal intensity that leads to out of a proportion perception of loudness. So what that means is, okay, you're testing someone's hearing, and you increase the sound stimulus by just a little bit, but the person goes, oh my gosh, that's really loud. Right? So that's an out of proportion response, where they should have just noticed a little jump. Right? So why is that important? Well, because it's a very interesting phenomenon that can suggest there may be something like Meniere's disease. Another thing called rollover can be affected or can be found when you do a hearing test, And that's a paradoxical decrease in discrimination ability with increasing stimulus. Okay. So what does that mean? Well, when you increase the stimulus, usually you can hear it better. Right? It's louder. Right? So you can say, oh, yeah. I can definitely hear that. But the person actually tells you, oh, the hearing my my hearing is actually getting worse. So it's a paradoxical decrease in perception. Right? So, again, there's something weird going on, and that may suggest there could be a retrocochlear disease like the acoustic neuroma, the brainstem tumor. Retrocochlear means it's more medial towards the auditory pathway. Tone decay in fatigue. Yeah? Is it still considered rollover if you have a hearing aid or a cochlear implant? Because I think that in those cases, it becomes distorted if it's loud. That's a that's a completely different, when you hear with a cochlear implant, it's, the sound stimulus. It's, you're converting, really electrical energy in a different way. So, yeah, you can't believe this is sort of for people with sort of normal structural ears. Tone decay and fatigue describes when you have reduced auditory perception with a sustained stimulus. Game suggests retrocochlear disorder. So let's say that I give you a sound stimulus for 10 seconds at the same level. Normally, you should hear it the same for 10 seconds. K? But in someone with tone decay or fatigue, the sound goes down. Perception of sound goes down the longer it is. K? So, again, these are sort of interesting findings on an audiogram. That's very important because that points you to where the hearing, abnormality may be within the auditory pathway. Okay. Now when you get a pure tone audiogram, there are different sort of shapes or configuration that you can get. So it may be flat relatively flat like this. It could be rising. It could be sloping, which is very common type of hearing pattern hearing loss pattern. Or it could be a little cookie bite that's called. Right? So the cookie bite means someone took a chunk out of the middle. Someone took a bite out of it. Right? So cookie bite is important to know because that tells you this is some type of a hereditary genetic or familial hearing loss. Right? So you can get a lot from a well done audiogram. Now when you get a pure tone again, you can talk about the severity of hearing loss. Right? Generally speaking, the frequencies are on the horizontal or x axis, and the vertical axis denotes the sound sound stimulus levels. Yeah? I was just wondering with the E by Jake, how do you know know that that's, like, specifically a hereditary hearing loss? How do I know that? Yeah. Like, what's the reason why that would occur, I guess? It's just It's just Okay. Yeah. Just a well known hearing pattern. Sure. Okay. Yeah. So hearing levels you can have, obviously, normal hearing. The worse sort of the lower you go, the worse your hearing levels are. Right? Because it means the intensity has to be really loud for the person to say they can hear it. Right? So the lower it is, the worse it is. Now the cutoff really depends on what textbook views or what population. Like, pediatrics is a little bit different than adults for what's mild loss versus moderate loss, for instance. Because kids can hear better generally. Right? So you don't have to know the details of where the cutoffs are, but just know that there's mild, moderate severe and profound. Profound means it's you're deaf you have deafness. Right? That's when we consider things like cochlear implants. Alright. Next concept to know in an audiogram is called masking. K? And we talked about masking briefly when we saw those symbols. But masking is actually when you're trying to actually mask mask noise so that you're testing the specific year that you're interested in. So it's actually a noise introduced. It's like a white white background noise introduced to, into the non test year to prevent crossover crossover of sound stimulus. So crossover is when you're trying to test, like, let's say you're trying to test the right ear, and actually the person is perceiving sound on the left ear. So that's crossover. So you don't want that to happen. Right? Because you want to get ear specific accurate results. Right? So masking is done to prevent the crossover. Right? So you're making sure you're testing the correct ear. Now the way the ear works, air conduction crossover happens when there's a discrepancy in the hearing levels of about 40 decibels or greater. K? So when you have a headphone on, if you produce sort of the not super intense sounds, you're not it's not gonna cross over to the other side, unless it's really loud or really intense. The bone conduction, though, crosses over at any intensity. And that makes sense. Right? Because how is bone conduction done? Right? Never. It's like a vibratory thing. A bone oscillator in the mass story. And our skull is connected. Right? So you can feel that on the other side. Right? So technically speaking, it's not always done because, for instance, it's difficult to do in kids. But technically speaking, when you do bone conduction, you should be masking it. Otherwise, you may not be testing the correct unit. Ear. Now there's this thing called masking dilemma is when you have significant conductive hearing loss because so the sound stimulus has to be so loud. There's no amount of mask masking you can do. It's always gonna cross over. So that's called masking delay. And there are other ways to bypass that by doing other tests, but not in a regular one. The last part of the audiogram, again, so we did pure tone speech audiometry, and then we're gonna do impedance testing. Acoustic impedance. So acoustic impedance, there are 2 parts called tympanometry and acoustic reflex testing. So they're the 2 final parts of the audio. So tympanometry is done by using this very simple looking probe that goes into the ear canal. And then you press a button and it produces this pressure like energy. So energy is produced, it hits the eardrum, and it bounces back and gets detected by this probe. So it's basically so the way I want you to think about it is it's testing basically how the eardrum is moving when there's pressure energy that's transmitted to the eardrum. So the result you get is what we call a tympanogram, and they look like this. So this is a type a tympanogram that's normal. Type a is normal. All the definitions are on the next slide. So type a is normal. So what does this mean? Well, so the, so the x axis is actually decoPascals and its pressure levels that's generated and. So what I want you to think here is so that probe is producing energy. It's hitting the eardrum. Right? It's hitting the eardrum, and it's moving in and it's moving in and then back out. So it's sort of going in and then out. K? So you want the peak of that eardrum movement to be around 0. Could be a bit plus or minus 50 or so that could have scale type. So that's sort of the result you want. Right? So normal eardrum with that energy hits it, moves in and out. Okay? Don't worry too much about these 2. But there's a type b. Type b is when there's there's flat, so it doesn't move. So the energy is hitting the eardrum, but it doesn't move. It's stationary. Okay? Type C is it's moving. So the eardrum is moving, but on a very negative pressure range. Okay? So those are the 3 sort of the most common results we get. Okay? So again, we're gonna talk about instances why where you can get type b or type c tympanograms. Let me cover otitis median at their top. But, again, this testing shows the compliance of the eardrum movement. Right? So for instance, if you have fluid in the middle ear space, you may get a type b tympanogram. Or if you have correct prolong eustachian tube dysfunction, then you can get what we call type c tympanogram. We'll again go into that when we talk about those specific disorders. So the next part of the cadence testing is called acoustic reflex testing. Acoustic reflex is provided through this the smallest muscle in your body. That's called the stapedius muscle. The only picture I can find was I think this is German, but, but it's a tiny little muscle that connects to the middle of your bone, to the neck of the malleus, or the stapes, sorry. So what do muscles do? What do muscles do in general? Relaxing contract. Yeah. They're relaxing contract. Yeah. So that's what this muscle does too. And that's a part of a reflex. So what happens in acoustic reflexes when you hear so let's say that you're at you're at Citadel Hill at noon. What happens at noon there? Yeah. The cannon goes off. Right? So it's a loud intense stimulus there. Right? So if you have normal hearing, your acoustic reflex will kick in. Right? It's protecting your ear from loud intense bursts, like the chemical analog. So what happens is if the ear perceives that kind of sound stimulus, this muscle contracts. Right? So when that muscle contracts, it makes the ossicles stiff. So it's not moving in as much, the stapes, into the inner ear or the cochlea. So it dampens the sound energy transfer. And that's a reflex, just like your patella knee reflex. You don't have to do anything, it just happens. Now it's a bilateral reflex, meaning, let's say the cannon went off on my right side, the reflex that's just worked on this side, it also goes to the contralateral side. But the ipsilateral response is a little bit stronger than the line. And the why the reason why it is bilateral is because there's this crossover at the the reason why it is bilateral is because there's this crossover at the brainstem. Again, don't worry too much about all of these things, but the sound stimulus gets felt through the ape nerve, right, the cochlear vestibular nerve or the cochlear nucleus, goes to the superior oleveric complex, and then that's where it crosses over to the other side, to the facial nerve nucleus, and then to the same side, and then it contracts the stapedius muscle, which is supplied by the facial nerve on both sides. K? So if you again, if you have this picture of the pathway in your mind, if there is no acoustic reflex, right, it's either there or not, it's absent or it's yes or no, present or absent. It's not like you have different degrees of it. So if there is no acoustic reflex, then anything along this pathway can be affected. Meaning that if you have some type of a hearing disorder and you don't perceive that sound stimulus, the reflex may be absent. But also if you have a facial nerve disorder, that's the efferent part. Right? You may be perceiving the sound, but the efferent part of the reflex or the output part may not be functional. So there are many different reasons, as shown here, where there could be absent reflexes. Conductive hearing loss, sensorineural hearing loss, brainstemnations, all of that stuff that can affect anywhere along that path. K? Now when you do reflex testing, there's this thing called decay testing kind of similar to tone decay and fatigue. So the reflex is maintained for a few seconds, but in some individuals, the response of the acoustic reflex decays or gets lessened over a few seconds. So that also suggests possibly a brain stem or central nervous system problem. Okay. So couple more things, and then we'll be done. So there so that's the audiogram. Right? Important parts are their 3 distinct parts, and they all have to agree with each other. The beauty of the audiogram is, again, it's this testing sort of different parts in a different way. Right? And some of those things like rollover recruitment can really point you towards your next test you may need to do or referral you may need to do. But there are other auditory measurements that you can do. Right? Things like electrococliography, which is basically e EMG or electromyograph myography of different auditory pathways, cochlear potentials. Don't worry too much about the first two. But OAEs or auto otoacoustic emissions and ABRs or auditory brainstem response, we do have to know a bit about we'll come back to this when we cover newborn hearing screen. But OAEs, there's few different types, like transient, evo, distortion product. Don't worry about the different types. But OAEs, simply put, are these sort of mechanical like sounds generated from the, outer hair cells in the cochlea. Right? So that's where we think it's coming from. So it's either there or not, kinda like acoustic reflex. It's either yes or no. OA's are present. You can hear those things from the outer hair cell or not present. So when you this is a very simple auditory measurement we can do. That's why it's used in newborn hearing screen. Right? You connect the probe, you push a button, and it tells you it's either there or not there. And again, if it's there, that means you you can assume that the cochlea is functioning normally. Again, these OEs are generated from other hair cells, which is in the copia. ABRs, it's a bit more involved because, again, it's basically, you have to put a bunch of electrodes on. It's testing or it's measuring the electrical activity in your auditory brain stem pathway. So so this easy way to remember the auditory brainstem pathway is the is the acronym e coli. So E is a nucleus or nerve, c is the cochlear nucleus, both superior allomeric complex, and so forth. Okay? So when you do these measurements, you get sort of all these sort of messy waves. Right? So this is a lot more involved than just doing an ABR, where you put a probe in and you push a button, and you get present or absent result. Yeah. This takes time. This takes the patient to be asleep or be reclined. So you measure all of these activities, and, basically, when you combine them, you start forming these waves. There's a pattern of waves that you see, and we've gained it. It's pretty controversial still what wave is what part of the aortatory brainstem pathway. But, basically, different waves, peaks correspond to different parts shown here. So, again, you wanna see sort of these distinct waveforms telling you that the the brainstem part of the auditory pathway is working normally. Okay. So this is one of the longer lectures. There's a couple more sort of longer, but usually we'll finish much earlier. Okay. So again, now we have a basis of terms, bit of anatomy review, bit of knowledge about hearing test. Now we can start talking about real disorders. And, again, you know, having the terms or everything you sort of learned solidly in your mind will help throughout the course. Okay. So, again, next Monday, we don't have a lecture, so I'll see you in 2 weeks.