Week 3 notes
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This 23 page Class Notes was uploaded by Mary Sullivan on Sunday September 13, 2015. The Class Notes belongs to CSD 4330 at University of Missouri - Columbia taught by Kelly Clay in Summer 2015. Since its upload, it has received 26 views.
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Date Created: 09/13/15
Intro to Audiology 08272015 Impact of hearing loss on individual and society Prevalence of hearing loss 0 91 out of every 1000 individuals in the US have signi cant hearing loss in one or both ears 0 1 out of every 1000 infants in the US is born w severe to profound heanngloss Prevalence increases w age Prevalence more than doubles if you consider individuals older than 65 years of age 0 Why 0 Increase of war 0 Baby boomer generation aging ConsequencesImpact of hearing loss 0 Factors that in uence impact of hearing loss on the individual and the society 0 Severity of loss Outcome is very different if the loss is unilateral and mildmoderate that if it is a bilateral profound loss 0 When it is acquired Prelingual before birth to about 3 years Perilingual 34 years Postlingual 5 years and older 0 Age intervention begins Studies showing intervention before 612 months of age has signi cant impact 0 Type of intervention Hearing Aid Cochlear implant assistive devices Manual vs oralaural Signi cant hearing loss can also affect other aspects of life Psychosocialpersonalitybehavioraltraits Anatomyphysiologyacoustic review 0 External ear Pinna or Auricle 0 Common landmarks Function of outer ear 0 Protection 0 Ampli cation o localization 0 Middle ear also called the tympanic cavity consists of an air lled cavity 0 Primary structure are 3 bones malleus incus and stapes known as the ossicular chain Left Earl Pars Flaccicla ight Ear Long Process of incus Equot Marlubnum 9 I of Malleus g E a Ume 5 r Pars Tense 7 Light Fleflex Annular Light Flaflex Cone of Light Ligament Cone of Light Figure 2 8 Major otoscopic landmarks of the tympanic memlbrane Cone of light GOOD Quadrants of Middle Ear o Anterior superior o Anterior inferior o Posterior superior o Posterior inferior Protection 0 General anatomy of the external ear and ear canal serves to protect the middle ear and therefore also the brain Localization Differences between ears in level and arrival time at the two ears are used to localize sound in space wout a pinna our ability to localize sound would be poor 0 the pinna is used to determine if sound is coming from the front or the back of the head Anatomy of Middle Ear Tympanic membrane ear drum Ossicular chain Function of middle ear Impedance matching 0 Vibrations in a low impedance medium air must be transferred to vibrations in uid higher impedance medium 0 Structure and function of ossicles allows for impedance matching 0 Limited protection against loud sounds 0 Middle ear muscles contract re exively in response to intense sound and stiffen the ossicular chain Impedance matching is accomplished primarily by 0 Difference in area of the tympanic membrane TM and the stapes footplate 171 or 246 dB Pivc point for o Ossicles vibrate around an axis that is not on center Pressure at the stapes footplate is increased bc the fulcrum of the ossicular level system is closer to the stapes than to the TM 131 or 23 dB Anatomy of Inner ear Hair cells sit on top of the basilar membrane 3 rows of outer hair cells 1 row of inner Along w hair cells and basilar membrane we have the tectorial membrane Movement of the BM causes the hair cells to move therefore beginning an action potential towards the brain Tecmrial membrane Basllar membrane Pivot point for i g g 4 Shear Force Displacement Force Functions of the inner ear Lecture 2 Air and Bone Change in mechanical vibrations of the uidmembranes of the inner ear into neural impulses which can then be transmitted to the brain Perform frequency analysis 0 Not ass neurons in the auditory nerve are stimulated for every sound Low frequency sounds activate apical neurons High frequency sounds activate basal neurons Outer hair cells of the normal cochlea 0 Change length when stimulated Elongate and contract with the stimulus 0 Function is to amplify or enhance the movement of the basilar membrane near the peak of the traveling wave 0 Normal OHC function results in low thresholds and good frequency discrimination 91 The Basic Audiologic Evaluation 1 Case history 2 Otoscopy 3 Audiogram Air conduction testing ii Bone conduction testing 4 Occlusion effect and tuning fork tests Case History Identifying information Presenting complaint Hearing historycommunication dif culties 0 Differences between ears use a hearing aid history of noise exposure etc Otologic history ear surgeryinfections Family history General medical history General impressions Tinnitus ringing in the ears and vertigo When communicating Listen 0 Stay in control 0 Address patient rather than spouse or accompanying family members This applies to interviews of older children as well 0 Ex is the patient able to talk to you or hisher spouse in a normal conversational voice but claims heshe cant hear 0 Pay attention to the patient s behavior Otoscopy Look for Occlusionforeign bodies in canal o Might block eardrum examples are cotton earwax possibly sores Signs of drainage swelling growths in ear canal Examine the pinna for lesions Collapsing canals not an issue anymore 0 Status of Tympanic Membrane TM 0 quotcone of lightquot 0 perforationsretractionsin ammation uid on basis of otoscopy you need to consider o Is a medical referral needed If so now or after the hearing test 0 What should be expected to nd during the hearing test Conductive pathology 0 Normal TM Middle Ear Semitranslucent Concave light re ex or cone of lightquot Pars tensa and pars accida Manubrium of the Malleus Long process of the lncus Umbo Annular Ligament Quadrants Anteriortowards front superiorabove Anterior inferiorbeow Posteriortowards back superior Posterior inferior Rule of thumb If you can t see a portion of the TM have the ears cleaned before testing Cerumenear wax removal is done by some audiologists Make sure you have liability insurance appropriate tools and training 0 Err on the side of caution Serous otitus media with bubble means there is uid in the ear and there are air bubbles associated with it Exotosis there are multiple bony protrusions in the ear canal bony growths are thought to be the result of exposure of the ear to cold water such as swimming or sur ng in cold water 0 People who can get this are deep sea divers sky divers Perforation hole in the TM can also come with tympanoschlerosis thickening of the TM Looks white build up of plaques on the eardrum tends to be associated with otitus media It will result in some stiffening of the movement of the TM 0 Looks like a potato chip not a contact lens healthy TM Result of many ear infections When perforation and eardrum rupture occur can have blood on pillow child can wake up screaming but will feel better once uid drains Audiogram 0 Two mechanisms for getting sound to the cochlea Air conduction 0 Normal route Pressure variations in air in canal cause TM movement ossicular vibrations pressure variations in uid of cochlea traveling wave 0 Most ef cient way of hearing 0 Bone conduction 0 Sound transmitted through vibrations in bone to the cochlea Vibrations in the bone result in pressure variations in uid of the cochlea These are results in a traveling wave 0 Air conduction audiometry Measure sensitivity or acuity at various frequencies Determines degree of hearing loss but not type of hearing loss Asses functional integrity of outer middle and inner ears Tests all 3 0 Transmission of sound through outer ear and middle ear to cochlea Present sound through earphone Earphones Supraaural earphones o TDH 39 49 or 50 headphones Q Mounted in MX 41AR cuchions Etymotic research ER3A transducers with tubephone insert earphone Earphone placement 0 Place quotredquot earphone on right ear 0 Place blue earphone on left ear 0 Threshold procedure 0 Usually test better ear rst 0 Continuous or pulsed tone 0 Start at 1000Hz at 30dB Use modi ed HughsonWestlake threshold procedure ASHA mandated standard everywhere 0 First ear 1000 2000 4000 8000 1000 500 and 250Hz Second ear 250 500 1000 20004000 and 8000Hz 0 Can use either methods of threshold 0 Test halfoctave if there is a 20dB or greater difference between adjacent octaves 0 Repeat 1000Hz threshold bc the threshold usually improves as the test continues Usually don t write threshold the rst time o Octaves 250Hz8000Hz is the range of human speech Want to test these 0 Hearing threshold levels 0 O for right ear air conduction threshold 0 quotRed right roundquot 0 X for left ear air conduction thresholds Pure tone averages PTA1 average thresholds for AC at 500 1000 and 2000Hz PTA2 average thresholds for AC at 1000 2000 and 4000Hz o 2 frequency PTA average of two best thresholds at 500 1000 and 2000Hz 0 pick frequency that agrees with your SRT 0 SRTPTA equation 0 Patients vary in 0 Age 0 Intelligence 0 Education 0 Motivation Willingness to cooperate Methods of instruction Spoken Written Gestures Sign language might have a patient who is deaf Demonstration Patient response Raise hand Raise nger Press signal button 0 Vocal response appropriate response for quadriplegic special procedures for children o conditioned play 0 visual reinforcement o behavioral observation Clinician s decision Instructions to patient 0 Will play a role in threshold but not by much Placement of bone oscillator Selection of earphones inserts are best Placement of earphones Selection of rst ear to test Selection of frequency sequence Selection of intensity selection of type of signal 0 Use a post signal for ringing in the ears 0 Air conduction Supraaural TDH 39w MX41AR cushions Insert earphones ER3A Speaker sound eld 0 Bone conduction Bone vibrator forehead or mastoid placement Tuning fork old school If levels get to be intense enough a signal transduced via either headphones or through the sound eld can result in bone conducUon Mastoid placement of the bone oscillator Can feel the mastoid or the bump behind the ear You want to place the bone vibrator on that mastoid bump Want to make sure it is stable doesn t slip Movement or poor placement can result in errors Bone conduction Stimulates whole skull Both cochleas are stimulated simultaneously Bone conduction thresholds tell you something about the sensitivity of the better of the two cochleas the better ear or better cochlea will respond 0 But don t know which cochlea ios better 0 For testing threshold 0 Start with lOOOHz go up then back to lOOOHz 0 Start with better ear 3 modes of bone condiction not testing on compressional component inertial component osseotympanic component 0 all 3 contribute to our ability to hear via bone conduction Compressional mode of BC o The skull vibrates causing compression of the cochlea This results in displacement of the uid of the cochlea resulting in budging at compliant points namely the oval window and the round window 0 Think water in water balloon The oval and round windows have different impedance and therefore don t expand to the same degree 0 The round window is more compliant than the oval window therefore compression of the cochlea pushes the uid in the scala vestibuli downward displacing the basilar membrane and setting up a traveling wave Osseotympanis mode Bony portion of ear canal moves with vibrations of the skull Remember the inner 23 of the ear canal is bone 0 Causes pressure variations in air in the external canal These pressure variations hit the TM set the ossicles in motion and result in TW in cochlea Inertial mode 0 Skull vibrates but ossicles have inertia can move freely are not rmly xed to skull Ossicles will therefore move out of phase with the skull and cause movement of the stapes footplate in the oval window and a TW ensues Occlusion effect Blocking the external canal changes the osseotympanic component of bone conduction o Sounding hollow in your hearquot plug your ears and talk 0 Will make speech sound louder Vibrations in the skull causes vibrations of air in canal that escape out the canal Blocking the external meatus results in a greater percentage of that vibration being transmitted to the TM and from there to the cochlea Conductive hearing loss also gives you an occlusion effect Pathology may mean that the ossicles are more strongly xed in the oval window harder to get them to vibrate than in a normal ear Vibration of the skull results in bigger pressure differential across the basilar membrane Enhances compressional component of BC 0 A stronger signal reaches the cochlea when bone conduction is presented with the ears occluded This results from the vibrations in the skull resulting in vibrations of air in the ear canal Typically these air vibrations will escape out the ear canal to the environment However when the ear canal is occluded or closed off a large number of these vibrations are transmitted to the TM resulting in greater movement of the TM which in turn causes the ossicles to move more resulting in a stronger movement of the stapes into the oval window setting up a stronger traveling wave Therefore occluded bone conduction thresholds are better than unconcluded ones and the bone conduction signal will sound louder with the ear covered than open Improvement decrease in bone conduction thresholds that is observed when the ear is occluded either via physical blockage of the ear canal or through presence of pathology in either the middle or the external ear Tuning fork tests Each fork produces a pure tone Forks are tuned so that they are at octaves around middle C 256 Hz Can use them to test AC hearing or BC hearing Not routinely done by audiologists Routinely done by physicians to corroborate audios Basic tuning fork tests Weber Appropriate when the patient has difference between hisher ears Fork is positioned on center of the forehead and patient is asked if they hear it in right ear or left ear Will lateralize the sound to ear with better BC thresholds If poor ear is conductive will lateralize to the poor ear If poor ear is sensorineural will lateralize to the good ear If hearing is symmetric will be perceived in center of the head 0 Put the tuning fork in the center of forehead ask which ear it is heard right left or middle of head Rinne Rlna Hold fork alternately at end of ear canal and at mastoid process 0 quotquotquot strike tuning fork then put here 0 Will have right and left ear report AC is generally more ef cient than BC w forks Normal hearingSensorineural loss 0 Will hear louder via AC than BC 0 Positive Rinne or louder through air Conducheloss 0 Will hear louder via BC than AC 0 Negative Rinne or louder through bone Present via BC 0 Strike tuning fork and put on mastoid bone Alternatey block and unblock ear canal W your nger 0 Ask quotIs there a difference when I plug and unplug your earquot If no then ear is already plugged lf normal or sensorineural loss will sound louder when canal is blocked Occlusion effect positive Bing lf conductive component blocking the ear canal will make no difference negative Bing Weber and Bing can be done w bone vibrator to double check your results Results can be confusinginaccurate in cases of mixed losses or if hearing loss is too severe Weber can be inaccurate if bilateral loss may not lateralize to either ear Audiometer Piece of equipment used when testing hearing 0 Allows us to adjust the frequency 0 Audiometers are very expensive 1200018000 If not broken don t update it Allows user to select different frequencies 0 Octaves 2508000Hz o Intensity can be varied systematically Need to be able to present signals that range from inaudible to level to levels that would be painful for normal hearing individuals Why Painful hearing won t be painful w individuals with hearing loss 0 Present speech via microphone at calibrated presentation levels 0 Present prerecorded stimuli CD andor tapes 0 Audiometers used in class will have 2 channels ASHA standard for pure tone testing procedures Standardized procedures for determining thresholds o Modi ed HughsonWestlake Procedure Standardized report format 0 Audiogram Establishes normative data set Audiogram Frequency is measured in Hz Test ictave frequencies from 2508000Hz Test 12 octaves if there is a difference in threshold of 20 dB or more at octave frequencies Level is measured in dB HL Loudness dB HL dB HL tested large number of young adults with no history of hearing loss or complaints of hearing problems Measured the lowest levels that they could detect for octaves between 250 and 8000Hz Measured thresholds in dB SPL Median of that normative group at each frequency was called 0 dB HL 0 0 dB HL at 1000 Hz 70 dB SPL o 0 dB HL at 250 Hz 255 dB SPL o 0 dB HL at 8000 Hz 13 dB SPL Remember that there is normal variability around the mean Some better then mean some worse 0 These tests determined the average threshold of hearing for young adults 0 dB HL is the mean threshold for this group as measured in dB SPL Right air conduction threshold red circlequot RED RIGHT ROUND Left air conduction threshold blue Xquot Bone conduction threshold with vibrator on the right mastoid lt to the left of the line as you look at the audiogram Bone conduction threshold with vibrator on the left mastoid gt to the right of the line as you look at the audiogram 0 When the cochlea responds and the lt symbol pops up it doesn t mean the right ear is the better ear It means the bone conductor was placed on the right ear The better cochlea is still responding 0 Instructions for audiogram test Give all instructions before you put on earphones Tell them what they will hear and indicate how you want them to respond Encourage guessing Reassure that you can hear them in the control room Position patient that you can see them but avoid having them able to watch your movements 0 H ughsonWestla ke Procedu re Start at 1000 Hz 30 dB HL Depending on the response of the patient go up in 205 or down in 105 until response changes Start up 5 down 10 bracketing procedure Find point where they respond 50 of the time o This is threshold Speci cally most use positive responses on 2 out of 3 ascending runs Do more if unsure Look for 50 point Mark audiogram and proceed to next frequency 1000 2000 4000 8000 1000 500 250 Hz 0 Procedure would go 50 40 30 35 25 30 35 hearing did not hear 35 is threshold of hearing 0 Difference between dB SPL and dB HL 0 dB SPL measure of signal intensity that is not frequency dependent Sound pressure is compared to a reference sound pressure 20 uPa That pressure represents an estimate of the lowest level that a human should be able to hear regardless of frequency 0 dB SPL 20logP120 uPa sound level meters measure the signal level in dB SPL Used for audiometer calibration The Basic Audiologic Evaluation 913 0 Case history Otoscopy Audiogram 0 Air conduction testing 0 Bone conduction testing 0 Speech testing Tuning fork tests Review Severity of Loss 0 Normal lOdB HL to 20 dB HL Mild 2040 dB HL 0 Moderate 4055 dB HL Moderatelysevere 5570 dB HL Severe 7O 90 dB HL Profound 90 dB HL and worse Con guration of loss Flat Sloping worse in highs Rising worse in lows Steeply sloping Cookie bite Corner Type of loss Sensorineural difference between AC and BC thresholds is 10 dB or less No ABG Conductive difference between AC and BC threshold sis greater than 10 dB and the BC thresholds are es than or equal to 20 dB HL ABG gt 10 dB Mixed Difference between AC and BC thresholds is greater than 10 dB but BC thresholds are worse than 20 dB HL ABG gt 10 dB Testing procedures Start in better ear or right ear Find AC in both ears and then switch to BC 0 Do everything under headphones Get into a routine 0 Pure tone average PTA 0 Average of 500 1000 and 2000 Hz AC thresholds 0 Gross method of quantifying degree of loss 0 Compares well with threshold for speech PTAquot2 average of best 2 frequencies from that range 5 1k and 2k Hz 0 Calculated in cases with steeply sloping loss Masking Masking is a procedure by which we can obtain ear speci c threshold information 0 Need to know When you need to mask Why you need to mask Have a rough idea of how you mask 0 What is masking 0 When one sound interferes with perception of a second sound 0 Can be either ipsilateral or contralateral Why do you mask 0 To eliminate the nontest ear from the test situation 0 When do you mask 0 Any time the signal presented via either AC or BC is suf ciently loud that there is a possibility it could be perceived in the nontest ear The nontest ear could be responding o Essentially whenever there us a chance that the response could be from the nontest ear 0 Depends on interaural attenuation Crossover Vibration from tone presented to test ear is great enough to cross the skull and vibrate cochlear uids in nontest ear 0 Need to mask Cross hearing Stimulus presented to test ear is perceived in nontest ear 0 Results in erroneous threshold for test ear Crossover during AC 0 Sound presented to test ear can reach cochlea of nontest ear by 0 Bone conduction pathways 0 Air conduction pathways lnteraural Attention Sound becomes weaker as it traverses bones of skull from one side of head to the other 0 Difference in decibels between level of signal at test ear and level of signal at opposite cochlea 0 Will be softer on one side vs the other lnteraural attention for AC 0 During earphone testing amount of interaural attenuation depends on 0 Individual subject You could be testing a really big person Big person more energy IA 0 Frequency spectrum of test signal 0 Type of transducer supraaural or insert earphone Amount a sound is attenuated as it crosses the head Assume 0 dB for BC stimuli There are very conservative estimates Varies across individuals and transducers o 40 dB conduction interaural attenuation is very conservative estimate for human subjects 0 Everyone will lose 40 dB so if you use this criteria will always mask when necessary Supra40 inserts60 0 You may also mask when you don t need to but better to err on the side of masking when not needed than not masking when you don t need to o For BC interaural attenuation can also vary however should use 0 dB again will always mask when needed Crossover via boneconduction ute Cochlea Cross over via boneconduction route Bone Vibrator Earphone Figure 9 3 Signal crossover and cross hearing occur via the boneconduction route to the opp051te cochlea as indicated by the arrows for both a bone conduction and b air conduction 0 Figure A shows the signal crossover from bone conduction Crosshearing occurs via bone conduction because remember BC occurs via vibration of the skull therefore you are stimulating both cochlea s simultaneously
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