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 are beyond today’s lesson FYI…Spontaneous Emissions are present in 60% of normal ears, present in females twice as often as males (3)

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 Middle ear state Noise in room Noise of subject Debris in EAC Response is calculated above the noise floor 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 LeftRight 2K: 152K: 30 3K: 353K: 80 4K: 354K: 85 6K: 406K: 60 8K: 158K: 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 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 non- cooperative 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? (6) Combination of two words 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 H 2 O

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