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ComD 3700 Basic Audiology Lesson 13 Acoustic Reflex Highlighted information refers to a change between the audio recording (using 10th edition) and the 11th edition of the textbook 1. COMD 3700 for Distance Education. This is lesson 13 on acoustic reflexes. This lesson will cover pages 162-167 in Chapter 6 of your textbook. 2. We have been discussing immittance testing. We learned about static compliance and tympanometry. The last immittance test we will cover in this course is acoustic reflex testing. Acoustic reflex testing consists of threshold testing as well as decay testing. However, we will only be discussing the acoustic reflex threshold test in this course. We will also not be covering testing for Eustachian tube dysfunction in this course. I just want to mention briefly that the presence of ET dysfunction can be determined subjectively through a history of patient symptoms or objectively by means of direct or indirect measures. In the most basic sense, Eustachian tube function can be assessed with conventional tympanometry. As we discussed in lesson 12, if the tympanogram demonstrates greater than -250 daPa middle ear pressure ET function is considered abnormal. 3. In the last lesson we discussed tympanometry. The diagnostic immittance machines we discussed are also used for acoustic reflex testing. After the tympanometry testing is completed, then the next test administered is the acoustic reflex. So the patient stays seated with the probe in their ear. The same probe tip that was used for tympanometry is used for acoustic reflex testing. In addition a headphone or insert earphone is placed in the opposite ear. On this slide are 2 examples of an immittance machine where you can see the probe tip for tympanometry and acoustic reflex testing and also the earphone or headphone that is placed in or over the opposite ear. Most of the time the patient is set up initially with the insert earphone in the opposite ear from the probe tip. Then after the tympanometry testing, acoustic reflex testing is started. You should always conduct a tympanometric test before making any acoustic reflex measurements. Some machines automatically perform the acoustic reflex test following the tympanogram. The patient instructions for the AR testing would be similar to the tympanometry testing. You should inform the patient that they will hear a series of beeps or tones in their ear. They do not need to respond to the tones in any way and should try not to move or startle during the loud measurement. 4. Before we can begin to study the acoustic reflex, you have to understand the anatomy and physiology associated with the acoustic reflex threshold. This includes the outer, middle and inner ear structure, the vestibulocochlear (VIIIth cranial nerve) and structures of the central auditory nervous system (CANS); specifically the auditory structures located at the level of the lower brainstem including the cochlear nuclei, superior olivary complex and facial nerve (VIIth nerve) nuclei. If you have taken COMD 3400 or another anatomy of hearing course, then you will have studied this. It is important to remember that there are two muscles associated with the middle ear, the tensor tympani and the stapedius muscle. The facial nerve innervates the stapedius muscle and the stapedius muscle contraction is responsible for the acoustic reflex threshold. 5. The acoustic reflex is defined as the contraction of one or both of the middle ear muscles in response to an intense sound. The contraction of these muscles results in increased impedance or lowered compliance. It is important to understand the nature of a reflex. A reflex occurs below the level of cognitive control. In other words, we do not have to think about it. For example, this is why you pull your hand away quickly when you touch a hot stove. You don’t have to first think, “Wow, my hand is burning”. Your reflexes pull your hand away instantly. In this manner, the stapedius muscle contracts in response to a loud sound, even though the patient does not control the action. This is to protect the ear from the damage associated with loud sounds. As I mentioned earlier, there are two muscles associated with the middle ear, the tensor tympani and the stapedius muscle. When a loud sound enters a normal ear, the stapedius muscle will contract on both sides, regardless of which ear is stimulated. So, the AR is a bilateral (two side) reflex. Adequate stimulation in one ear results in an acoustic reflex occurring in both ears at the same time. There is a very small time difference. But for all intents and purposes, stimulus in one ear results in a response in both ears at the same time. Therefore, in AR testing we measure the pathway stimulated in both ears. The words ipsilateral and contralateral are used to report the test results. The ear with the immittance probe is called the probe ear, while the ear receiving the stimulus is called the stimulus ear. The word ipsilateral, sometimes referred to as ipsi, means the same side. The probe ear and the stimulus ear are one in the same. The stimulus and the measurement occur in the same ear. Contralateral, or contra, means opposite side. The probe ear and the stimulus ear are different. The stimulus is presented to one ear, while measurements occur in the opposite ear. So, these terms refer to where the AR is measured relative to where the loud sound is presented. If the AR is measured on the same side in which a loud sound is presented, then it is an ipsilateral AR. If the signal is measured in the opposite side to that in which the loud sound is presented, then it is a contralateral AR. The results are reported by the ear that is stimulated by the signal. 6. One additional way to remember this is, if the tone is presented on the probe side, then it is an ipsilateral AR. If the tone is presented on the earphone (which may be an insert earphone) side, it is considered a contralateral AR. So, right and left results in AR testing refer to the ear that is stimulated by the loud sound. If the signal goes into the right ear and the AR is measured in the right ear then it is called a right ipsi AR. If the signal goes into the right ear and the AR is measured in the left ear, it is called the right contralateral AR. This can be confusing when reviewing the results. Remember that the results refer to the stimulated ear. So in this “patient” we are testing the right ipsilateral ART and the left contralateral ART. We will discuss this in more detail when we review the testing process. 7. To understand the implications of AR testing, it is important to have a basic knowledge of the acoustic reflex pathway also called the acoustic reflex arc. This is the path of the acoustic stimulus. There is a diagram on page 164 of your textbook of this pathway. To me, it is easier to understand when viewed as a model like I posted on this slide. This is the acoustic reflex pathway. It bears just about no resemblance to the actual anatomical structures which are extremely small, three-dimensional and much more complex in terms of the nerve projections. However, this figure illustrates the main AR pathways and most of the key structures. The stimulus ascends from the outer ear to the brainstem and then descends via the facial nerve on both sides of the head to innervate the stapedius muscles in both middle ears. In this simple model of the acoustic reflex pathway the acronyms are as follows: ME = middle ear, IE = inner ear, VIII = vestibulocochlear or auditory nerve, CN = cochlear nucleus, SOC = superior olivary complex, VII = facial nerve. It is important to note that two of the structures in the pons (SOC and VII nucleus) are shown together for simplicity. The book just refers to the SOC at this level. They are actually separate structures. A branch of the facial nerve ends at the stapedius muscle and the stapes is shown as a stirrup-shaped stick figure. So, imagine first a normal right ear and trace the pathway of a loud signal. The signal enters the right ear, travels through the outer, middle (ME) and inner ear (IE), along the VIII nerve, to the brainstem. When the signal reaches the brainstem, the signal arrives first at the cochlear nucleus (CN). From here, the signal travels to both right and left superior olivary complexes and both right and left facial nerve (VII) nuclei. The signal is sent from both facial nerve nuclei to both facial (VII) nerves, which results in a contraction of both stapedius muscles. Thus, both stapes bones are pulled outward and downward, in a direction away from the inner ear. This action makes it harder for energy to travel through the middle ear (increase in impedance/decrease in admittance). The lowest intensity level at which this contraction is measurable is the Acoustic Reflex Threshold (ART). We will study the ART after we study the various pathways in greater detail. 8. This model represents the right ipsilateral pathway. Remember that in ipsilateral testing the stimulus and the measurement occur in the same ear. So the stimulus is presented in the right ear through the probe, it travels through the outer, middle (ME) and inner ear (IE), along the VIII nerve, to cochlear nucleus (CN). The signal then travels to the right superior olivary complex and right facial nerve (VII) nerves. It is then measured by the probe as a contraction made by the right stapedius muscle in response to the sound. 9. In the right contralateral pathway, the probe ear and the stimulus ear are different. The stimulus is presented to the right ear through the earphone, while measurements occur in the left ear. So the signal enters the right ear, travels through the outer, middle (ME) and inner ear (IE), along the VIII nerve, to the cochlear nucleus (CN). From here, the signal travels to the left superior olivary complex and is sent from the left facial (VII) nerve, to the left middle ear, which results in a contraction of the stapedius muscle. The result is then recorded by the probe placed in the left ear. 10. The left ipsilateral pathway will be the same as the right (except on the other side). So the stimulus is presented in the left ear, it travels through the outer, middle (ME) and inner ear (IE), along the VIII nerve, to cochlear nucleus (CN). The signal then travels to the left superior olivary complex and left facial nerve (VII) nerves. It is then measured as a contraction made by the left stapedius muscle in response to the sound. 11.The final scenario is the left contralateral pathway. Here the stimulus is presented to the left ear through the earphone, while measurements occur in the right ear. So the signal enters the left ear, travels through the outer, middle (ME) and inner ear (IE), along the VIII nerve, to the cochlear nucleus (CN). From here, the signal travels to the right superior olivary complex and is sent from the right facial (VII) nerve, to the right middle ear, which results in a contraction of the stapedius muscle. The result is then recorded by the probe placed in the right ear. Now that we have learned the reflex pathway, we will discuss the specific reflex tests. 12. When conducting AR testing, the first test we will perform is the Acoustic Reflex Threshold (ART). As I mentioned, this is the lowest level at which an AR can be obtained. So similar to finding the threshold for pure tone air and bone conduction testing and speech testing, we will now be finding the threshold for the acoustic reflex response. Of course, the difference is that this threshold test is objective. An acoustic reflex threshold is a middle ear measurement of stapedius muscle response to higher intensity and adequate duration sounds for individual frequencies. Consider the softest sound that elicits a reflex contraction of the stapedius muscle as the acoustic reflex threshold. When the stapedius muscle contracts in response to a loud sound, that contraction changes the middle ear immittance. This change in immittance can be detected as a deflection in the recording. We have learned that tympanometry records changes in middle ear immittance, while air pressure is varied in the ear canal. Acoustic reflexes are recorded at a single air pressure setting. It is tested at the pressure setting that provided the peak immittance reading for that particular ear on the tympanogram. Ear canal pressure is maintained at that specific setting, while tones of various intensities are presented into the ear canal and immittance is recorded. A significant change in middle ear immittance immediately after the stimulus is considered an acoustic reflex. Acoustic reflex thresholds generally are determined in response to stimuli of 500, 1000, 2000, and 4000 Hz. For screening purposes, or for a general check of the pathway's integrity, clinicians usually test at 1000 Hz. The book states that the normal acoustic reflex responses occur with a stimulus of 85 to 100 dB SPL. To determine the ART, a pure tone signal is introduced at 70 dB. If no compliance change is measured, then the level is raised in 5 dB steps until a response is seen. The highest level at which the AR should be tested is 115 dB HL. If there is a measurable response at 70 dB, then the level is lowered by 10 dB until no response is measured and then raised in 5 dB steps until the threshold is determined. The criteria to constitute a response varies depending on the equipment you are using. But a response amplitude of .02 ml - .03 is very commonly used. The ART results can help in provide information about the site of pathology in a hearing loss, the approximation of degree and type of hearing loss in non-cooperative patients, the facial nerve integrity and more. The AR is used to help differentiate cochlear from retrocochlear pathology. Retrocochlear refers to abnormalities along the auditory pathway beyond the cochlea, including the auditory (VIIIth cranial) nerve or within the auditory brainstem. Other tests are necessary for confirmation of a site of lesion suggested by the AR. One can suspect, but cannot diagnose, site of lesion based solely on the results of AR testing. 13. Hopefully seeing an actual printout of the ART responses will help make this clearer. This is one example of the ART results. As you can see the top row is being tested using ipsilateral (same ear) stimulus and the bottom row represents contralateral (opposite ear) stimulation. The stimulus frequency is 1000 Hz. The probe is in the right ear. The stimulus intensity is listed for each presentation and the response amplitude is listed below the presentation. 14. So, in this test, the probe is in the left ear. We are testing 1000 Hz. Testing begins at 80 dB HL. A response amplitude of .05 is measured, so the stimulus is lowered to 75 dB and a response of .03 is measured. 0.2 ml is considered a pass for this equipment, so the stimulus is lowered to 70 dB. This time the response amplitude is only .01 ml. This is not considered a response, so the intensity is raised to 75 dB and a response of .02 ml is measured. 75 dB would now be considered the ART for the left ipsilateral test at 1000 Hz. The patient would have heard 4 tones or beeps in their ear during the testing, but would be unaware of any reflex occurring or measurements being made. Next contralateral testing would begin. On this printout, the results are reported by the probe ear, so the left ear is still reported as the probe ear. But this is actually a right contralateral AR. The stimulus is presented from the right earphone, although the probe tone is still heard in the left ear though the probe. The change in compliance is measured in the probe in the left ear. So at 80 dB the response amplitude is .04 ml. So the level is lowered to 75 dB, but a response of .01 is not an adequate response, so it is raised to 80 dB HL. A response of .03 is recorded. So the right contralateral ART is 80 dB at 1000 Hz for this patient. 15. The results are usually recorded on a graph located on the audiometric worksheet. So this patient had ipsilateral reflexes at 85 dB at 1000 Hz and at 80 dB at 2000 Hz in the left ear. The picture is representing that the probe is placed in the left ear. The stimulus is also in the left ear. The left contralateral results are 100 dB at 500 Hz, 90 dB at 1000 Hz, 85 dB at 2000 Hz and 90 dB at 4000 Hz. Note that the picture shows the probe in the right ear, but the stimulus is being presented through the left earphone and measured in the probe in the right ear. So this is the left contralateral response. This is important to remember before we move on. 16. Here are 2 more examples of how the ART may be recorded. The NR responses on the graph represent No Response. So there was no recordable AR. The lower graph just lists the results as normal or absent. It may also be recorded as elevated or present at high sensation levels. Some clinicians refer to normal results as present, present at normal sensation levels or within normal limits (WNL) as well. We will discuss what the results indicate next. 17. Once you have obtained the ART results, then they must be interpreted. There are a number of result outcomes for the acoustic reflex threshold. The textbook highlights four. Most responses fall into one of these categories. The four categories are present at normal sensation level, absent, present at low sensation level or present at high sensation level. Notice that the results are categorized according to sensation level (SL). Remember that the sensation level is the number of decibels above the hearing threshold of a given subject for a given signal. So it varies by patient dependent on their hearing level. If a patient has a threshold of 0 dB HL and a stimulus is presented at 85 dB HL, then it would also be 85 dB SL for them. They would perceive the stimulus as being 85 dB. However, if they have a hearing loss of 20 dB, then a signal of 85 dB would only sound like 65 dB to them. So most normal hearing individuals will have a reflex when pure tones are introduced to either ear at 85-100 dB SPL. This is because their pure tone threshold is 0-15 dB. So the SL for them would be the same as the normal range of 85-100 dB for the ART response. However, if they have a pure tone threshold of 50 dB, then the ART will not be measured because it would not be present until 85 dB SL or 135 dB HL. The results are reported as dB HL. Most of the recording and interpretation of the ART are done using the actual dB HL results. But you can also interpret the ART based on the SL. So in order to do this the audiometric (pure tone) thresholds would have to be obtained. The pure tone thresholds would then be subtracted from the dB HL ART to obtain the SL of the ART. So if at 1000 Hz patient had a ART of 90 dB HL and a audiometric threshold at 1000 Hz of 40 dB, then the sensation level of the ART would be 50 dB SL (90 dB response of ART-40 dB HL audiometric threshold=50 dB ART SL). You would then determine what 50 dB SL is considered. Hopefully that helps rather than confuse you. I just wanted to make sure you understood what is meant by the descriptions of normal, low and high sensation levels. Okay, so now we will go over each outcome briefly so that when you see the results you will understand what might be causing them. The first is outcome is that the ART are present at normal SL. This occurs when the acoustic reflex threshold at about or near 85 dB SL or 85-100 dB SPL. A normal ipsilateral acoustic reflex threshold suggests that a large conductive component is not present in that ear. If reflexes are present, sensorineural hearing loss is probably no worse than moderate in degree, and the ipsilateral acoustic reflex pathway is largely intact. The next outcome is absent results. This means that there were no reflexes recorded at a great enough amplitude, even if tested at 115 dB. This indicates that the patient has a hearing loss. It may be a conductive hearing loss or a moderate to severe SNHL. The absence of acoustic reflexes warrants investigation. If the ART are present at very low sensation levels, less than 60 dB SL, this is due to the fact that the person is recruiting loudness, which narrows the sensation level or the distance between audiometric threshold and the acoustic reflex threshold. So for example, if a patient had a 50 dB hearing loss they may show a reflex at 95 dB HL. This would be 45 dB SL. This can indicate a mild to moderate SNHL associated with cochlear lesions. In this situation it is important to realize that the ARTs occur at about normal levels (85100 dB). This is because the acoustic reflex threshold in an ear with a cochlear (SNHL) loss may resemble the results of a normal ear when the air conduction thresholds are below about 50dB HL. As the hearing threshold increases above this level, the chance of recording an absent or elevated acoustic reflex increases. In the last category, ARTs are present at a high sensation level. This is also referred to as elevated ART responses. If the ART are present at high sensation levels, greater than 100 dB above the audiometric threshold, it can be due to a conductive hearing loss in the stimulus ear. If abnormally elevated ARTs are not caused by a conductive disorder then the patient is considered to be at risk for a retrocochlear pathology in the ear that receives the stimulus. This is usually due to damage in the auditory (VIIIth) nerve. Again, it is not advised to introduce a signal greater than 115 dB HL. So this occurs when the results are present at a level higher (105-115 dB) than we would expect for the degree of SNHL or in a patient with normal hearing. 18. There are 10 theoretical examples of various results on page 167 of your textbook. I do not want you to worry about memorizing this chart. I am more concerned with making sure that you can look at the ART results and understand what area of the pathway is affected. In looking at the chart the “patient” is set up for 4 different test conditions. From left to right, they are right contralateral testing, Left ipsilateral testing, right ipsilateral testing and left contralateral testing. Each test can have different results (present, absent, present at low SL and present at high SL). As you look at the conditions down the side (A-J) you can determine what ART results you would expect to find with each condition. I want to go over a few of these, to get you used to determining what the results indicate. In the first condition the patient has normal hearing in both ears. So all results should be normal. This means that the acoustic reflex pathway stimulated both ipsilateral and contralateral from both the right and left ear are all functioning normal. 19. In this situation the right ear has normal hearing and the left ear has a mild to moderate cochlear hearing loss. So, are the ART results consistent with this condition? The right ipsilateral and contralateral results to are normal, so we can rule out any problems in this area. The left ipsilateral and contralateral results are present at low SL. Due to the common loudness recruitment issues found in cochlear (SN) hearing loss, this is to be expected. 20. So when we take the results and put them on the chart, it points to normal hearing in the right ear and mild to moderate SNHL in the left ear. So yes, the findings are consistent. 21. In this situation there are no results. No acoustic reflexes were measured in the right ear or the left ear by contralateral or ipsilateral stimulation. So there are no acoustic reflex pathways that are functioning normally. This is consistent with a bilateral severe SNHL. 22. As you can see if you take the results and place them on the chart, it confirms that the patient has a moderate to severe SNHL. 23. With this slide just look at the results first and then we will determine where the damage has occurred in the pathway. This is normally all you will have, just the numerical results. So first we have to determine the category they belong in. The right ipsilateral reflex is 85 dB, this is considered normal. The contralateral right ear and ipsilateral left ear reflexes are absent. The left contralateral threshold is 105 dB. This is considered elevated. So what do these results indicate? To determine this, I think it is easiest to sketch in the pathways for ARTs that are normal. After obtaining an individual patient’s ARTs, the pathology can be localized to the area that is not highlighted. So, the right ipsilateral ART responses are present at normal levels. So we know this pathway is intact. Everything else is affected. The right contralateral ARTs are absent. We have determined that the ipsilateral pathway is normal, so we know the problem must be occurring at some point beyond the right cochlear nucleus. This points to the left ear. In looking at the left ear, the left ipsilateral responses are absent, so we know the problem is occurring in between when signal is presented to the middle ear and when it is measured in the middle ear of the left ear. The left contralateral is elevated or absent. We can determine that this is because the signal must cross whatever is causing the problem in the left ear and reach the cochlea of the right ear loud enough to cause a reflex. 24. When we put the results on the chart we can determine that the right ear is normal. The absent reflexes in the right contra and left ipsi (probe ear) stimulation indicate a conductive hearing loss. In addition the elevated reflexes in the left contralateral (stimulus ear) stimulation point to a conductive hearing loss as well. 25. In this scenario, you have a conductive hearing loss in the left ear. With a ME Pathology anything that goes through the left ear or is measured in the left ear can be affected, depending on the severity of the pathology. The ART may be affected for signals traveling through the left ear (L ipsi or L contra) or signals measured in the left ear (L ipsi, L contra). 26. In this slide the results have been provided, but as practice I would like you to go through the pathways and the chart to determine the condition for the right and left ear. 27. In this example, the site of lesion has been provided for you. What you need to be able to do is predict ipsilateral and contralateral acoustic reflex thresholds for the right and left ear based on this information. You should be able to look at the results of the ART and determine the condition and also predict the ARTs based on the pathology of the ear. 28. In conclusion I want to let you know that as clinicians, we need to combine findings from the entire audiological test battery to make appropriate recommendations for further testing, medical referrals, amplification, and so forth. Always keep in mind when conducting ART testing, that ARTs are not meant to be used alone, but as part of a battery of tests to help in the evaluation process. This chart, located in your textbook on page 187 is helpful in using the tympanogram type, static compliance results and the ART to help determine the type of hearing loss. 29. For those of you continuing in audiology the acoustic reflex decay along with additional electroacoustical and electrophysical procedures will be discussed at length.