Physiologic Measures
Physiologic Tests in Audiology
Otoacoustic Emissions Evoked Potentials Immittance Measures
Alphabet Soup of Audiology
OAE, DPOAE, TEOAE, AABR, ABR, MLR, T-grams, MNR, P300… WHAT in the WORLD are those tests?
When would they be used? What do they mean?
Otoacoustic Emissions
Just About Everything You Want To Know About OAE
Origin Types of Tests Interpretation
Otoacoustic Emissions
First reported by Dr. David Kemp in England in 1978(2)
Two types of emissions are routinely measured
Transient Evoked OAE Distortion Product OAE
Benefits of each type
FYI…Spontaneous Emissions are present in 60% of normal ears, present in females twice as often as males(3)
are beyond today’s lesson
Structures of the Inner Ear(1)
Cochlea - Snail-shaped
organ with a series of fluid-filled tunnels Rests deep in temporal bone of skull Footplate of stapes rests in oval window of cochlea
cochlea of guinea pig
Hair Cells of Cochlea
Frequency-specific
High frequency sounds, basal end of cochlea Low frequency sounds, apex of cochlea
So What IS an OAE?
(4)
OAEs are actually soft sounds generated by the movement of the structures (outer hair cells) in the cochlea Stimulation is sent in through the middle ear, emission occurs within the cochlea, sound then must travel BACK OUT through the middle ear, external ear and be recorded by the microphone of the device
What IS an OAE?
• OAE will likely be observed if auditory threshold is between 0dB and 30dB/40dB HL(5)
• Variables influence OAE
Response is calculated above the noise floor
Middle ear state Noise in room Noise of subject Debris in EAC
1-2dB, up to 20dB
Measured across frequency range
TEOAE
Transient Evoked Otoacoustic Emission Abrupt Click or Tone Burst activates the cochlea across a wide frequency region, if outer hair cells are normal, TEOAEs are produced(4) TEOAE amplitude/noise floor difference calculated at individual frequencies, usually 1K Hz to 5K Hz Stimulation usually presented at 80dB SPL
Transient Evoked OAE
•The patient has an auditory threshold of 50dB HL at 4KHz in the left ear, otherwise hearing is within normal range
Distortion Product Otoacoustic Emission - DPOAE (6)
Stimuli for DPOAE are two closely spaced pure tones, called f1 and f2…the calculated response is actually the intermodulation
distortion product
produced by the ear when stimulated
DPOAE
Usual frequency range for stimulation is 500 to 10,000 Hz Due to noise floor, difficult to obtain results below 1500 Hz Variable stimulation, generally 55dB SPL and 65dB SPL for f2 and f1, respectively Tones across frequencies presented
Distortion Product OAE
•Auditory thresholds 0-5dB HL, each ear; patient is 41 year old female
DPOAE with Hearing Loss
52 yr male; Audio results Left Right 2K: 15 2K: 30 3K: 35 3K: 80 4K: 35 4K: 85 6K: 40 6K: 60 8K: 15 8K: 60
Use for Otoacoustic Emissions
Sensitive measure of outer hair cell function Important for early identification and diagnosis of auditory dysfunction in pediatric and adult populations Useful for screenings in newborn nurseries Can confirm soundfield results in toddlers Can substantiate results that are “questionable” in adult patients who attempt to feign a hearing loss
How to Interpret OAE?
NOT A TEST OF HEARING…RATHER, A TEST OF OUTER HAIR CELL INTEGRITY Results provided by frequency ranges, found to correlate with hearing in normal range Report summary will state at which frequencies the responses were obtained
Auditory Evoked Potentials
Terms, Definitions and Reasons to Request AEP Tests Interpretation of AEP Tests
Auditory Evoked Potential Tests
ABR, ECochG, AMLR, ALR, P300, MNR, 40Hz Tests are far field recordings of neurophysiological responses to auditory stimulation…in a bioelectric background!(4) Alteration of time windows, filters, and/or stimuli will change the response…for some tests, special equipment is necessary
Auditory Brainstem Response (ABR) Tests
The most well known, the ABR, discovered in 1971(7)
Primarily used to evaluate neurological disorders at level of auditory nerve and brainstem
ABR not significantly affected by most drugs or subject state of arousal
Auditory Evoked Potential Tests
ABR allows tracking of electrical energy via the auditory neural pathway to level of inferior colliculus(8) Presence of Wave V found to be reliable estimate of hearing ability in 2K-4K Hz range(8)
Results tracked to within 10-15dB of threshold Latency/Intensity functions can indicate conductive loss, high frequency loss, severe to profound loss…BUT, will miss low frequency loss(6)
Auditory Evoked Potentials
Can be used as auto screen method, AABR for Pass/Refer Patient must be quiet, relaxed; infants asleep or sedated Click stimuli provides information about 2K to 4K Hz region of cochlea Can use bone oscillator to perform bone conducted ABR
Auditory Evoked Potentials
Possible to construct an “audiogram” based on ABR results obtained with 500Hz, 1000 Hz, 2000 Hz tone bursts Used to identify auditory dys-synchrony (auditory neuropathy), a dysfunction of neural pathways(9,10)
Auditory Evoked Potentials
Likely abnormal in
Patients with Multiple Sclerosis and other demyelinating processes Hyperbilirubinemia at levels requiring exchange transfusion Patients with severe high frequency loss
ABRs, like OAE, NOT a test of hearing, but of neural function, neural synchrony
Auditory Evoked Potential Test
Subject variables that affect results(8)
Age
Gestational age at least 27 weeks to observe ABR Latency, amplitude change in expected fashion
until 18-24 months, when ABR becomes adult-like Extensive normative data available by age range
Gender Muscular artifact
Other AEP Tests
AMLR Auditory Middle Latency Response ALR Auditory Late Response P300 Event Related Response 40Hz Variation of MLR On-going studies regarding clinical utility of these tests continue Most recorded since 1960s(6)
Not in widespread use outside of research sites
Why Request an Evoked Potential Test?
Can be used to construct an audiogram in patients incapable of voluntary responses (infant, mentally handicapped) In adults, rule out retrocochlear or demyelinating process
More Reasons to Request AEP
To construct an audiogram in noncooperative adults (malingering) To identify auditory dys-synchrony (auditory neuropathy) (10) To assess aided thresholds when behavioral testing not possible (13)
Auditory Evoked Potential Tests
Not necessarily first line of testing for Audiologists!! When referring children/infants for auditory evaluation, evoked potential tests may be the last needed, following soundfield, OAE, BOA, VRA, etc. Sedated ABRs can often be avoided, use other methods first
Immittance Measures
Tympanogram Acoustic Stapedial Reflex
External Auditory Canal
Approximately 2.5 cm in length “S” shaped Lined with cerumen and sebaceous glands Outer 1/3 cartilage; inner 2/3 temporal bone(1)
What IS Immittance?
Combination of two words
(6)
Admittance is the reciprocal of Impedance Acoustic admittance is a measure of the flow of energy through middle ear and impedance is the opposition to this flow
No better, quicker or less expensive single audiologic procedure exists to assess status of middle ear, cochlea, eighth nerve and lower brainstem than a complete Immittance Battery
Tympanic Membrane(1)
Thin membrane, made of three layers Forms boundary between outer and middle ear Vibrates in response to sound Changes acoustical energy into mechanical energy
The Ossicular Chain(1)
A Malleus B Incus C Stapes
Ossicles are smallest bones in the body, fully formed at birth Act as a lever system Footplate of stapes enters oval window of the cochlea
Eustachian Tube(1)
Lined with mucous membrane; connects middle ear to back of the throat (nasopharynx) Equalizes air pressure Normally closed except during yawning or swallowing Not a part of the hearing process, but status can influence hearing ability
Stapedial Muscle (11)
Connects the stapes to wall of middle ear Contracts in response to loud sounds; known as the “Acoustic Reflex” Can be stimulated ipsilaterally or contralaterally
Valuable Information/Simple Test
Test results reveal
Ear canal volume(6) Children 0.42ml to 0.97ml Adults 0.63ml to 1.46ml
Peak amplitude of tympanogram Pressure point of peak
Normal values +/- 100mm H2O
Tympanogram Types
Modified Jerger Classification System(6)
A(d) A A(s) B C
Some Thoughts in Closing…
•Physiologic test measures in Audiology may be used on patients of any age and provide valuable information about auditory-neural functions •While these tests are NOT direct tests of hearing, information about the auditory system is provided •Otoacoustic Emissions •Auditory Evoked Potentials •Immittance Measures