Physiologic Measures

1
Physiologic Measures

• Physiologic Tests in Audiology
• Otoacoustic Emissions
• Evoked Potentials
• Immittance Measures

2
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?

3
Otoacoustic Emissions

• Just About Everything You Want To Know About OAE
• Origin
• Types of Tests
• Interpretation

4
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 todays lesson

• FYISpontaneous Emissions are present in 60 of
  normal ears, present in females twice as often as
  males(3)

5
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
6
Hair Cells of Cochlea

• Frequency-specific
• High frequency sounds, basal end of cochlea
• Low frequency sounds, apex of cochlea

7
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

8
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

9
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

10
Transient Evoked OAE

• The patient has an auditory threshold of 50dB HL
  at 4KHz in the left ear, otherwise
• hearing is within normal range

11
Distortion Product Otoacoustic Emission - DPOAE
(6)

• Stimuli for DPOAE are two closely spaced pure
  tones, called f1 and f2the calculated response
  is actually the intermodulation distortion
  product produced by the ear when stimulated

12
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

13
Distortion Product OAE

• Auditory
• thresholds 0-5dB HL,
• each ear patient
• is 41 year old female

14
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
15
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

16
How to Interpret OAE?

• NOT A TEST OF HEARINGRATHER, 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

17
Auditory Evoked Potentials

• Terms, Definitions and Reasons to Request AEP
  Tests
• Interpretation of AEP Tests

18
Auditory Evoked Potential Tests

• ABR, ECochG, AMLR, ALR, P300, MNR, 40Hz
• Tests are far field recordings of
  neurophysiological responses to auditory
  stimulationin a bioelectric background!(4)
• Alteration of time windows, filters, and/or
  stimuli will change the responsefor some tests,
  special equipment is necessary

19
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

20
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 lossBUT, will miss low frequency loss(6)

21
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

22
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)

23
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

24
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

25
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

26
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

27
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)

28
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

29
Immittance Measures

• Tympanogram
• Acoustic Stapedial Reflex

30
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)

31
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

32
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

33
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

34
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

35
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

36
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

37
Tympanogram Types
Modified Jerger Classification System(6)
A(d) A A(s) B C
38
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