ROUGH EDITED COPY
EHDI CONFERENCE
Audiology 101 Introduction to Audiology for Nonaudiologists Working in and Supporting EHDI Activities
2:00 P.M. 3:00 P.M. (ET)
FEBRUARY 27, 2017
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CART CAPTIONING PROVIDED BY:
ALTERNATIVE COMMUNICATION SERVICES, INC.
P.O. BOX 278
LOMBARD, IL 60148
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This is being provided in a roughdraft format. Communication Access Realtime Translation (CART) is provided in order to facilitate communication accessibility and may not be a totally verbatim record of the proceedings.
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>SPEAKER: Well, good afternoon, everyone. Welcome to Audiology 101, which is an introduction to audiology for nonaudiologists working in and around EHDI programs and supporting EHDI activities. I'm Jeff Hoffman with the National Center for Hearing Assessment and Management. I want to introduce my copresenter.
>DR. FOUST: Good afternoon. Sorry about that.
I'm Terry Foust, and I'm a pediatric audiologist and speech language pathologist, and I've been a consultant with NCHAM's Early Childhood Outreach programming project and based in Salt Lake City, Utah, and I'm happy you elected to join us after lunch, and we appreciate your attendance.
>MR. HOFFMAN: So at the end of the next 60 seconds we hope that you'll be able to is this better to hear me? Is that better volume? Okay.
We hope that you'll be able to identify the parts of the auditory system, describe how the ear works. I can do this. I can do this.
Describe the types and degrees of hearing loss. Describe how hearing loss is assessed and diagnosed as well as describing the types of treatment and intervention that's available for hearing loss.
We're going to start by just a very brief overview of what audiologists are. Audiologists are specialists in hearing and balance, and you know, one aspect of the work is in the prevention of hearing loss the identification, and assessment of hearing loss and balance problems and then in the rehabilitation or habilitation in persons with hearing and balance disorders.
With the EHDI programs with newborn hearing screening most of the focus in fact all of the focus is on the hearing aspect rather than the balance aspect.
This is a cross section of the ear. And we're going to go through and look at the different parts of the ear starting from the outside toward inward. So there are four parts to the auditory system. There's the outer ear, the middle ear, the inner ear and the central auditory nervous system.
So we'll start with the outer ear. Whoops. The part that we see of our ear is called the pinna, and it's a fleshy portion, and it really doesn't do much. It's great to accessory eyes sometimes but not much to do with hearing. The external auditory canal, also called the ear canal is funnels sound towards the auditory system, and it's about an inch long, and kind of S shaped, kind of curved. And at the end of the outer ear portion, the end of the ear canal is the similar pan nick membrane or eardrum, and that serves as the boundary between those two parts of the auditory system. This is a picture of the eardrum. You'll notice that it's this is a healthy eardrum. It's kind of a pearly gray color. And it's somewhat translucent. You can barely start to see one of the ears of the middle ear bone here.
Wow, that is supposed to be a pointer, but it's not working.
So in the center up to about the 1o'clock position on that eardrum is where the one the bone to the middle ear is attached to the tympanic membrane.
The next part beyond the eardrum is the middle aerospace. It's basically a cavity. It's an airfilled cavity. And it contains three bones, the smallest bones in the body, and we'll look at those in just a second, but those bones serve to transmit sound to conduct sound from the ear canal that has been con through the tympanic membrane, vibrated the tympanic membrane, eardrum, and it keeps transmitting that sound forward, those vibrations and the process the eardrum, and the three bones increase the strength of those vibrations at that time are coming in and the sound that's coming in, the sound energy that's coming in at this point gets trans transposed to a mechanical energy, so we've got a transfer of energy there.
Another part of the middle aerospace, the middle ear system is the eustachian tube, and that's a tube that connects that middle ear cavity to the back of the throat, and it serves to equalize the pressure between our external environment and that middle aerospace. So how many of you flu into Atlanta in the last couple of days? A lot of you did. Were your ears at some point a little bit stuffy when you were ascending or descending? Well, that's because that eustachian tube hasn't yet opened up and equalized the pressure. So let's say you're landing, your ears are stuffy. You know. You chew gum. You swallow, something like that, that opens that eustachian tube and equalizes the pressure between the two.
Here's a picture of those three little bones in comparison to a dime. They are the smallest bones in the body. And from the left to right it's the hammer, also called the malleus or the incus is the middle one, also called the anvil. And then the stapes or the stirrup is the smallest one there, and these are connected by ligaments and they're also very, very small muscles that are attached to them. And those muscles can contract in response to loud sounds and kind of stiffen that system up and prevent some of that sound from being transferred on to the inner ear. So it serves those muscles serve as a little bit of a protective mechanism.
The third part is the inner ear, and this sat part that gets really fascinating as far as all of the parts. There are two parts to the inner ear. One a part of it has to do with balance, and the other part has to do with hearing. So we're going to focus on the hearing part, and that's the cochlea which is that little snailshaped section that you see offer to the right of the screen there, and it's fluidfilled. It's in the skull cavity, and it's filled with fluid. There are three different chambers that are filled with fluid, and it contains the end organ of hearing by is called the organ of corti, and it also had many thousands of hair cells or sterocillia, and we'll take a look at those in just a second.
So when that sound comes in through the ear canal, vibrates the eardrum, transfers through the those bones and gets to the cochlea, it pushes that fluid back and back and forth, and those little hair cells get bent very slightly. And as they bend, they generate electrical stimulus that then goes on up to auditory nerve to the brain.
Here's a picture of the hair cells. You'll see that there are three rows of those little V shaped ones. Those are the outer hair cells and then there's one row of the inner hair cells. Terry will talk a little bit later about one of the hearing tests that has to do with those outer hair cells of the when they get bent they produce an oat toe OAE, if they're functioning normally, and that's one of the tests that are used in newborn hearing screening.
Another aspect of the hair cells is that their frequency specific. Depending on where they are in the cochlea, they respond to different pitches, to different frequencies.
And the fourth part is the auditory nerve and the central auditory nervous system, and this the auditory nerve has more than 25,000 nerve fibers, so it's once a again lots of little parts, lots of things going on when sound comes in, and that auditory nerve transmits that electrical signal up through the brainstem and to the level of the auditory cortex.
So now we've gone from a sound pressure to a mechanical to an electrical signal, and then once it gets to the cortex, to the brain, that's where we assign meaning to it. That's where we recognize what different sounds are. So when I snap my fingers, (snap), we think that was a finger snap. So that's that's happening at the auditory cortex.
There's a really good You Tube video. It's about 7 minutes long that's called auditory transduction by BrendonSpletsch, and if you want to see a really nice demonstration of how all of this works, take a few minutes SPLETSCH, and I'll show it later, but it's kind of fascinating, at least for me. I hope you might find it fascinating to see how the ear works on that.
When we think about hearing loss, when we talk about hearing loss we want to think about all of the different ways that we see can describe different types of hearing loss. The first way that we can describe hearing loss is by how many ears are involved. So if only one ear is involved it's called a unilateral hearing loss.
If two ears are involved then we call a bilateral hearing.
We also can describe hearing loss by where in the auditory system there's a problem. If we have a problem in the it outer or middle ear, it's called a conductive hearing loss because it doesn't conduct the sound. So if your ear canal is plugged with wax or, you know, Mardi Gras is coming up sometimes Mardi Gras beads get put in kids ears or other things, that's a conductive hearing loss because it's blocking the sound from being conducted inward.
If a child has a middle ear infection that has fluid in that middle ear space that also prevents that sound from being conducted on into the auditory system. So problems in the outer ear and the middle ear are called conductive hearing losses.
There are two types of conductive hearing losses. There can be permanent ones and temporary or transient ones. So the Mardi Gras beads, the fluid, those can be treated medically. The Mardi Gras bead which can be removed, the wax, the fluid, and middle ear treated and that fluid resolves so it's a temporary or transient hearing loss.
But if there are malformations in that let's say that there's atresia where there's no ear canal, that's more of a permanent hearing loss until there's a surgical treatment for it.
Another type of hearing loss is called sensorineural hearing loss, and that's when there's a problem in the inner entire or in the auditory nerve, and inner ear or in the auditory nerve and we have a mixed hearing loss which can be a combination of both a conductive hearing loss and a sensorineural hearing loss. So that would be a problem in either the outer ear or the middle ear and the inner ear. So that's why it's called a mixed loss. Both conductive and sensorineural.
And then we have hearing loss that's a result of problems in the auditory nerve or in the auditory central auditory system, and that can be called auditory neuropathy spectrum disorder. It used to be called auditory neuropathy dyssynchrony, and that has to do with disordered transmission of that electrical signal along the auditory nerve. And then the auditory system processing disorder has to do more in the cortex area.
Every year the centers for disease control and prevention ask all the early hearing detection programs in every state and territory to report certain data that they've collected every year, and that data has to do with how many has to do with the screening. It has to do with the diagnosis, and it has to do with the intervention that 136 that we've talked about that you've heard about in the last day.
And these are these are only the only data that's getting reported is called congenital hearing loss. Hearing loss that occurs at birth. We'll talk a little bit more about later onset hearing loss but at this point in 2014, which is the latest data that CDC has available, that about 40% of the babies who are identified with a permanent hearing loss had a unilateral hearing loss, a hearing loss in only one ear.
And then almost 60%. There's some unknowns in there, too, so not everything adds up to 100%, but about 60%, the most common type was a bilateral hearing loss, a hearing loss in both ears.
Now looking at the type of hearing loss, only about 13% of the congenital hearing losses are a result of problems in the utter ear or the middle ear, and those are those conductive hearing losses so that's not as common. The most common one is the sensorineural hearing loss which is a result of problems in the most often in the inner ear, in the cochlea, and that's almost 3/4 of the hearing losses are sensorineural.
Mixed hearing loss is fairly rare. Remember that's the one that has both a sensorineural and a conductive component, and that runs at about 8% of the babies who are identified with a congenital hearing loss.
And then auditory neuropathy spectrum disorder is also somewhat rare. About 8% of the babies who are identified with hearing loss at birth had auditory neuropathy. The incidence is a is greater for babies who have been in the NICU than for babies in the wellbaby. This is all combined, though for about 5%.
As a result of all of the data that CDC collects, we can start to look at how common is any type of hearing loss in the birth population, and this is all of these stats hold fairly steady from year to year. There's a little bit of variation, but about 1.6 of every 1,000 births, there's a permanent congenital hearing loss that is identified at birth. It's the most common birth condition.
And then as you've probably become aware of, there's an issue of loss to followup, loss to documentation in the EHDI system. Babies that don't get the followup diagnostics or they got it and it didn't get reported, and that's about 25% of the babies who didn't pass the newborn hearing screening. So actually the incidence is probably greater than that 1.6 because we have that missing group over there, that 25% that we don't know about of the babies who didn't pass that initial newborn hearing screening.
Hearing loss just doesn't happen at birth. It happens across the life span. And so by the time babies are growing up a little bit, by the time they're getting to school age, it's about 3 to 6 per 1,000 that have a permanent hearing loss, so it is increasing. With the early childhood outreach initiative, which looks at hearing loss hearing loss that's identified, you know, from birth to 3 years of age, we see an increase of about a doubling of this newborn hearing screening incidence.
We can also take a look at the causes of childhood hearing loss. In 2006, Morton published a retrospective Morton published a retrospective of the causes of hearing loss, and they were seeing the incidence at birth at 1.86, once again pretty consistent with what CDC saw in 2017 and previous years of 1.6, but about 21% of those hearing loss were the result of the GJB2 mutation.
So almost a little over 1/5 of the babies had that particular gene mutation that caused the hearing loss.
There were also some genetic aspects or genetic causes of hearing loss, both syndromic, and nonsyndromic, and combined about 65% or preponderance so of congenital hearing loss is a result of genetic factors.
Congenital cytomegalovirus, CMV is also cytomegalovirus CMV is another major cause, and it can be divided into CMV that's clinically apparent in that there were other symptoms that were identified as part of congenital CMV or clinically inapparent infection in which hearing loss was the only known or observed or diagnosed problem as a result of the congenital CMV.
Now when we go Morton also looked at hearing loss and the causes of hearing loss at 4 years of age, and they were seeing an incidence at that point of almost 3 percent 1,000. And combine all of the genetic factors, had gone to about 50% because there were other reasons that hearing loss later onset had come in and increased. And CMV was one of those. About 25% of the children at age 4 were a result of congenital CMV, some of which about about 10% was a later onset hearing loss.
So congenital CMV, hearing loss can occur at a later point in time, so that's about 10% of those hearing losses.
Part of figuring out what what audiology is all about is understanding an audiogram. Now, for young children, for babies, hearing does not get graphed on an audiogram. But it does give us an idea of what the the degree of hearing loss is. And as a baby grows into a young child, parents who have a child with a hearing loss, they will soon need to know about an audiogram.
So an audiogram graphs an individual's hearing sensitivity, and it includes both the type and the degree of hearing loss.
So across the top of the audiogram is frequency or pitch. And it goes from a low pitch on the left side to a high pitch on the right side. So think about a piano keyboard. Left is low, right is high.
The loudness of the sound is on the up and down, and it starts with a very soft sound at the top to a very loud sound at the bottom. And what an audiogram does is it it graphs the threshold of a person's ability to hear sounds at different pitches or different frequencies, so a threshold is the the level at which you can just barely detect that a sound has been presented.