Welcome to ACOUSTIC REFLEX TESTING: METHODOLOGY, INTERPRETATION, AND CLINICAL USES
Presenter: Ted Venema, PhD Faculty, HIS Program Ozarks Technical Community College Springfield, MO
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. This presentation is being recorded . CE credit is available! Visit ihsinfo.org for details . Note taking handouts are available at ihsinfo.org on the webinar page. Feel free to download now! Agenda
• A quick review of tympanometry
• Acoustic reflexes: contralateral and ipsilateral
• Interpreting acoustic reflexes
• Q&A (enter questions in Question Box any time) A QUICK REVIEW OF TYMPANOMETRY Tympanometry normally consists of four tests
1. Tympanogram types
2. Static compliance
3. Physical volume of EAM
4. Acoustic reflexes Function of the middle ear
2. 2. 1. 3. TM at rest Buckling action Umbo 1.
It increases sound pressure in three ways: 1. TM is larger than footplate of Stapes (17:1) 2. Leverage action of ossicles (Malleus is 1.3:1 longer than Incus) 3. Buckling action of TM (2:1) 120 Results in decibels 100
80 In Summary: dB 1. Eardrum – Stapes size: 17:1 SPL 2. Ossicles leverage action: 1.3:1 60 3. Eardrum buckling action: X 2:1 44:1 40 This corresponds to an increase between 30-35 dB 33 20
0 0 10 100 1000 10,000 100,000 1,000,000 Pressure Increase 44:1 The middle ear must increase the pressure of air-borne sound because the cochlea is filled with fluid! Key concept behind tympanometry
For the middle ear to be most efficient…
Air pressure must be even on both sides of TM
External Auditory Meatus (EAM) Tympanometry is really a test of middle ear efficiency
Speaker Tone in
Air Pressure changes
Microphone Tone out
When air pressure is equal on both sides of TM, this creates least stiffness; most compliance With greatest middle ear compliance
The middle ear is the least stiff, and it offers least overall Impedance
This means more sound will be able to go through it, and less sound will be impeded by it
Tympanometry measures this Low Hz (226Hz) tone at about 70 dB SPL… Bounces off normally stiff middle ear system
It is supposed to…That’s what you want otherwise, you have nothing to measure!
Speaker Tone in
Air Pressure changes
Microphone Tone out Test 1: The tympanogram; stages of otitis media
Type A = Normal Type C = Early OM with negative middle ear pressure Type B = Advanced OM with fluid Type A High
Type C
Compliance Type C going to Type B
Type B
Negative 0
Positive Air Pressure
Low Test 2: Static compliance oto-sclerosis, disarticulated ossicles, etc.
Type Ad • Lots of complicated High explanations around
about static compliance
Type As • It basically refers to
the “height” of one’s tympanogram! Compliance • How tall is your “tent!”
• Various pathologies Low affect static compliance Negative 0 Positive Test 3: Physical volume (PV) of ear canal
• Normally between 1.0cc to 1.5cc • A large PV might indicate a perforated TM • True type B tympanogram has normal PV • If type B with tiny PV, then probe tip against outer ear canal wall
TEST 4: Acoustic Reflexes Contralateral and Ipsilateral Location of Stapedius muscle
Lass & Woodford Hearing Science Fundamentals Fig 2-9 Lass & Woodford Location of Hearing Science Fundamentals Fig 2-10 tensor tympani muscle Brain Stem TT CN TT VIII nerve
SOCs V V Nerve Loud Nerve Sound VII VII Nerve Nerve S S Afferent Route Efferent Route Loud incoming sound V Nerve Middle ear VII Nerve Cochlea Tensor Tympani muscle (TT) VIII Nerve Stapedius muscle (S) Cochlear Nucleus (CN) Superior Olivary Complex’s (SOCs) The acoustic reflex arc • Afferent (going to the brain) path • Efferent (going from the brain stem) path back to the middle ears • Note crossover; a loud sound to one ear causes an AR in both ears Why do we have acoustic reflexes?
Ever listened to a recording of you? • You are the only one who hates the sound • Everyone else thinks it sounds just like you • That’s because you are hearing yourself by AC only • AC is how others hear you
Normally, you hear yourself by BC as well • Voice tone is richer, a bit lower • Also louder, which causes acoustic reflex • By AC, normal speech is 65 dB SPL • By AC and BC, your voice is closer to 80-85 dB SPL The purpose of acoustic reflexes is:
Not to protect against NIHL • One of the fallacies we are commonly lead to believe
ARs occur especially while we speak • they actually kick in about 50 msec before we talk
Note ARs strongest for low Hz’s (500, 1000Hz) • This is because our voices are louder for vowels
ARs reduce upward spread of masking • Allow us to hear better while talking • All mammals have them ARs are a low Hz phenomenon
Musiek & Rintelmann The acoustic reflex and tympanometry
With ARs, you are still using tympanometry • Measuring how much 226 Hz tone is bouncing off TM…
But while tympanometry changes middle ear compliance by: • Air pressures
ARs change middle ear compliance by • Loud sounds!
ARs are done at static compliance • At the air pressure yielding highest tympanogram
ARs thus normally restricted for: • Normal or near-normal tympanograms Acoustic reflex causes a temporary reduction in static compliance
High Normal Static Compliance
Compliance Reduced Static Compliance Due to Acoustic Reflex
Low Negative 0 Positive Air Pressure Acoustic reflexes are measured as temporary decreases in compliance (admittance)
Think of a temporary drop in the tympanogram peak (static compliance) while the loud AR stimulus is presented
The results here are shown for a 1000 Hz tone presented for one second
Musiek and Rintelmann Contralateral ARs were first to be developed
AR stimuli: 500 or 1000Hz tones at 85 to 110 dB HL • These are presented with headphone • Ongoing 226 Hz tone at 70 dB SPL in opposite ear measures AR • SPL increase at probe microphone indicates an AR Ipsilateral ARs came later
500 or 1000 Hz AR stimulus tone
AR stimuli: 500 or 1000Hz tones at 85 to 110 dB HL • Ongoing 226 Hz tone at 70 dB SPL in same ear measure AR! • SPL increase at probe microphone indicate an AR Acoustic reflex is always reported according to ear that got the stimulus
Stimulus and Stimulus in LE Probe in RE Probe in RE
Stimulus in RE Stimulus and Probe in LE Probe in LE
Katz Handbook 5th edition, page 207 INTERPRETING ACOUSTIC REFLEXES Hah!
Martin, F. Introduction to Audiology Seriously Though… Previous slide highlights why we don’t do both ipsilateral and contralateral ARs anymore
Cases A - F show conductive HL or SNHL • Note how if you cannot get ipsilateral ARs, you cannot get contralateral ARs • Similarly, if you cannot get contralateral ARs, then you cannot get ipsilateral ARs • That’s why for these cases, just run either ipsi or contra ARs
Cases G - K show retro-cochlear pathology • Note very different ipsilateral and contralateral AR patterns • Here it would make sense to run both ipsilateral and contralateral ARs • That however, was yesterday, this is today
If you suspect retro-cochlear pathology • Refer to an Audiologist who will run an ABR to look for retro-cochlear pathology or to a physician who will do a CT scans or an MRI to look for the same ARs reported in sensation level (SL)
ARs tested in dB HL (tympanometer calibrated in dB HL) • ARs normally found between 80-100 dB HL
ARs reported in dB SL (always relative to one’s own thresholds) • ARs can be tested at 500, 1000, 2000 or 4000 Hz
Normal and mild-moderate SNHL • May have ARs at similar dB HL • But at very different SLs
Eg: Normal HL and flat 50 dB SNHL may have ARs at 100 dB HL • But normal HL has ARs at 100 dB SL • The SNHL has ARs at 50 dB SL Conductive HL tends to obliterate ARs Case of unilateral conductive HL
Contralateral ARs with loud stimulus to bad ear: • HL in bad ear prevents intensity required to cause AR in opposite ear Contralateral ARs with loud stimulus to good ear: • Mechanical middle ear problems in bad ear prevent AR Ipsilateral AR absent in bad ear
Result: Only good ear Ipsilateral AR present
Katz Handbook of Clinical Audiology 5th edition, Conductive HL tends to obliterate ARs Bilateral conductive HL
Contralateral and ipsilateral ARs all absent
Katz Handbook of Clinical Audiology 5th edition, ARs and SNHL
Note: The SL for ARs tends to decrease linearly as the degree of SNHL increases up to about 60 dB HL SNHL and reduced SL
Note: SL decreases in almost exact proportion to degree of SNHL!
From Clinical Impedance Audiometry 2nd ed Jerger, Northern Absent ARs and SNHL
Note: Absence of ARs Increases dramatically with SNHL of 60 dB HL or more Bilateral SNHL and ARs Contralateral & Ipsilateral ARs Present
Katz Handbook of Clinical Audiology 5th edition, Unilateral SNHL (VIII Nerve Tumor) RE: Contralateral & Ipsilateral ARs normal LE: Contralateral ARs elevated; Ipsilateral ARs absent
Katz Handbook of Clinical Audiology 5th edition, Abnormal contra and ipsi ARs in client with intra-axial brain stem lesion
Katz Handbook of Clinical Audiology 5th edition, Relationship between degree of HL and absent ARs in SNHL vs VIII nerve pathology
Musiek & Rintelmann Contemporary Perspectives in Hearing Assessment ARs and speech discrimination
AR deals with IHCs • AR arc: IHCs send afferent information to VIII nerve • IHCs are critical part of AR arc
OAEs deal with OHCs • Cochlea: OHCs receive efferent information • OHCs not involved with AR arc
Two people with same moderate SNHL • May have very different SD
One with good SD probably has ARs at reduced SLs • One with poor SD probably has absent ARs Acoustic reflexes involve inner hair cells
• A very unique test under used today
• Oto-acoustic emissions involve outer hair cells
• Both are non-behavioral both obliterated by middle ear pathology
• They therefore make great cross tests
Fig 1-7, Venema, T. Compression for Clinicians 2nd edition, Thomson Delmar Learning 2006 Questions
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