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HESP706 > Otoacoustic Emissions > Flashcards

Otoacoustic Emissions Flashcards

1
Q

What did Thomas Gold discover?

A
  • 1940: cochlea is nonlinear (challenged Bekesy’s linear model)
  • Claim: inner ear contains mechanical resonators that actively process and tune auditory information
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2
Q

What did David Kemp discover?

A

-1978: OAEs

  • Origin is nonlinear mechanism
  • Respond mechanically to auditory stimulation
  • Dependent on normal functioning of the cochlear transduction
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3
Q

What are clinical uses of OAEs? (Kemp, 2002)

A
  • UNHS
  • Differential diagnosis
  • Monitor effects of treatment
  • Selection of treatment
  • Surgical options
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4
Q

What are research uses of OAEs? (Kemp, 2002)

A
  • Non-invasive window into intracochlear processes
  • Insights into mechanisms and function of cochlea
  • New understanding of the nature of sensory impairment
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5
Q

Describe TEOAEs.

A
  • Response to a click peaking at 84 dB SPL
  • Response level exceeds 30 dB SPL
  • Oscillatory log corresponds to TM motion
  • Can split response into different frequency bands to get frequency-specific information
  • Strongest TEOAEs from 1-4 kHz
  • Usually absent at hearing loss >20-30 dB HL
  • Widespread use in UNHS
  • Probe contains 2 ports
  • More sensitive to initial screen (cochlear dysfunction)
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6
Q

Describe DPOAEs.

A
  • DPs are Tartini tones, sensation of extra tones generated in the ear
  • Most robust response: 2F1-F2 where F1 is the lower frequency (60-70 dB SPL) and F2 is the higher frequency (50-70 dB SPL)
  • Most robust response 2-5 kHz
  • DPOAEs can be recorded with moderate hearing loss
  • No greater frequency specificity than TEOAEs
  • Probe contains 3 ports
  • Wider frequency range (differential diagnosis)
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7
Q

Describe pros vs. cons of OAE testing.

A
  • Pros: fast, simple, inexpensive

- Cons: high failure rate (especially in first 24 hours of life), does not detect ANSD

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8
Q

What are outer ear effects on OAE generation?

A
  • Wax, debris can block sound deliver tube or microphone
  • Leakage from improper fit
  • Ear canal acoustics
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9
Q

How can probe insertion affect OAE generation?

A
  • Leaky fit: loss of OAE signal, increase in ambient noise (extends test duration to achieve adequate SNR)
  • Blockage: unusually low noise floor and OAE levels
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10
Q

What are inner ear effects on OAE generation?

A
  • Sensitive to loss of OHCs
  • Affected by stria vascularis, which maintains electrochemical balance needed for normal OHC function
  • OAEs are byproducts of active cochlear processes
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11
Q

What is the function of IHCs?

A

-Sensory function: mediate conversion of mechanical energy to neural signals

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12
Q

What is the function of OHCs?

A

-Mechanical function: amplification for low-input signals (aka a little cochlear amplifier)

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13
Q

Describe the relationship between cochlear processes and OAEs.

A
  • Passive mechanism of the cochlea: important for propagation of stimulus energy to region where OAE is generated (driven by physical properties of cochlear partition)
  • Electrical processes of the cochlea: important for connecting passive to active mechanisms
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14
Q

What are 2 candidates for the biophysical basis for mammalian cochlear amplifiers? Which is most likely?

A
  • Voltage-driven somatic motility mediated by prestin

- Motility stereocilia bundles driven by calcium currents**

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15
Q

What are spontaneous OAEs (SOAEs)?

A
  • Level: -15 to 0 dB SPL
  • When detected, usually 3 or 4 SOAEs equally spaced along the basilar membrane (to accommodate logarithmic frequency mapping in the cochlea)
  • Reflects activity of the cochlear amplifier
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16
Q

What are 2 theorized mechanisms of SOAEs?

A
  • SOAEs in NAF ears are the result of active cochlear mechanisms/global resonances in the EAC
  • Isolated, high-level SOAEs are associated with cochlear damage (artificial boundaries along the cochlear partition act as barriers or reflectors, creating SOAEs)
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17
Q

What are 2 ways to record SOAEs?

A
  • Without external stimulation

- Click-evoked OAE subsides (~20ms) before evaluating signal in ear canal, called synchronized OAE

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18
Q

What are evoked OAEs?

A
  • TEOAEs
  • DPOAEs
  • Stimulus frequency OAEs (SFOAEs)
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19
Q

Why are SFOAEs difficult to record? How is the roadblock addressed?

A

-Generated OAE same frequency as the stimulus tone

  • Record with prove tone at the frequency of interest presented at 20-40 dB SPL
  • Suppressor tone close in frequency is added to the signal
  • Presence of the suppressor tone removes SFOAE from 2nd recording
  • 2nd recording is subtracted from 1st, so you’re left with SF emission
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20
Q

Describe mechanism-based classification of OAEs.

A
  • OAEs that arise from linear reflection (SOAEs, TEOAEs, SFOAEs)
  • OAEs that arise from distortion emissions (DPOAEs)
  • OAEs that arise from mixed emissions
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21
Q

Describe OAEs that arise from linear reflection.

A
  • Reflections from random perturbations “place fixed” along basilar membrane
  • Perturbations may constitute pre-existing irregularities in cochlear mechanics
  • Strongest reflections occur near peak of TW
  • When a few strong reflections occurring near peak of TW have coherent phase, reverse transmission of energy is initiated, portion of energy escapes the cochlea
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22
Q

Describe OAEs that arise by distortion emissions.

A

-Reverse transmission induced by distortion perturbations “fixed to the stimulus wave”

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23
Q

Describe unmixing procedures.

A
  • DPOAEs: isolate distortion sourceOAE by using 3rd stimulus tone near DP frequency to suppress amplification of reflection source wavelets
  • TEOAEs/SFOAEs: only study at low levels
24
Q

Describe the relationship between number of bits and dynamic range of an I/O device.

A
  • Number of bits of an I/O device determines its dynamic range
  • Dynamic range = 2^n, where n is number of bits
  • OAE systems are usually 16 or 24 bit systems, provided a dynamic range of 96 or 144 dB
25
Q

What are important aspects of the OAE probe?

A
  • Tubing designed to prevent cross-talk (leakage from sound source components)
  • Safeguards against entry of wax, debris
  • Moisture
26
Q

What are methods for eliminating OAE artifact?

A
  • Filtering frequencies not in the region of interest
  • Eliminate extra large signals
  • Repeatability
27
Q

What are the goals of calibration?

A
  • Present stimuli at precise, accurate levels

- Accurate representations of OAEs, noise floors

28
Q

What OAE output parameters should be calibrated?

A
  • Frequency
  • Amplitude
  • Time
29
Q

What problems arise from calibration in the ear canal?

A
  • Calibration signal is generated, portion of the signal is transmitted to the TM but another portion is reflected back to OAE probe
  • Results in standing waves for frequencies at/above 2 kHz
30
Q

What is the goal of future OAE calibration?

A

-Precise knowledge of the impedance characteristics of both the source (OAE probe) and the load (ear canal and TM) immediately before starting OAE measurement

31
Q

What pressure measure is most appropriate for OAE measurement?

A

-Forward pressure level (FPL): estimate of sound pressure on the TM (not reflection off TM so not contaminated by standing waves)

32
Q

What are key factors to OAE measurement?

A
  • Status of external and middle ear
  • Fit of probe within external ear
  • Stimulus characteristics and stability
  • Noise in test environment and within external ear canal
33
Q

How can standing wave interference be corrected?

A

-Repeat calibration and measurement after probe re-insertion

34
Q

Describe TEOAE stimulus parameters.

A
  • Type: click, tone bursts, chirps
  • Spectral characteristics: flat
  • Intensity: 80 or 86 dB SPL
  • Stability: percent variation in intensity level (>90%)
35
Q

Describe DPOAE test protocols.

A
  • Test with L1=65 and L2=55 dB SPL (increased DPOAE amplitude, enhanced sensitivity to cochlear dysfunction)
  • Higher stimulus levels increase likelihood of detecting artifact rather than actual OAE
36
Q

What are some problems with hearing screenings?

A
  • No national standards for the calibration of OAE or ABR
  • Lack of uniform performance standards
  • Problems with hearing-screening devices providing sufficient supporting evidence to validate specific pass/fail criteria
  • Audiologists must obtain normative data for the instruments and protocols they use
37
Q

Compare JCIH recommendations for WIN vs. NICU screening protocols.

A
  • WIN: either ABR or OAE, with repeat screening before discharge if first try is “no pass”
  • Some do 2-step protocol: OAE first, then ABR if OAE is “no pass”

-NICU: ABR, no pass babies get directly referred to audiologist

38
Q

What are some challenges of hearing screening?

A
  • Too many children lost to follow-up
  • Short of professionals with skills and expertise in pediatrics
  • Lack of timely referral for diagnosis, intervention of suspected hearing loss
  • Pediatric services poorly reimbursed
39
Q

Describe the AAA Childhood Hearing Screening Guidelines.

A
  • Use only when pure-tone screening not developmentally appropriate
  • Calibrate OAE equipment daily
  • 65/55 dB SPL
  • Screening programs must involve experienced audiologists
  • Failed OAE should receive tympanometry
40
Q

Describe DPOAE Input/Output functions.

A
  • Includes estimate of threshold and maximum amplitude
  • Utilized mostly for research
  • Objectively documented loudness recruitment
41
Q

What are non-pathologic factors that could influence OAE findings?

A
  • Time after birth
  • Time after bath (at least 7 hours)
  • Age
  • Sex
42
Q

What is the cross-check principle?

A

-No result should be accepted unless confirmed by an independent measure (i.e. behavioral audiometry, immittance, ABR, OAE)

43
Q

What are clinical applications of OAEs?

A
  • Cross-check
  • Monitor middle ear disease
  • Hearing screening
  • Monitor ototoxicity
  • Nonorganic hearing loss
  • SIDS (?)
  • APD
  • Differential diagnosis
44
Q

How does negative middle ear pressure affect OAEs?

A
  • TEOAE amplitude decreases 2.5 dB at +100 or -100 daPa (greatest changes for stimulus frequencies below 2 kHz)
  • DPOAE amplitude decreases 3.5 from 2-4 kHz
45
Q

What recommendations should be made if DPOAE amplitude changes are observed when monitoring ototoxicity?

A
  • Modify drug therapy (reduce dosage, increase time intervals between administration, substitute drug with another one with minimal/no risk of ototoxicity)
  • Therapeutic protection (i.e. antioxidants)
46
Q

What is the protocol for monitoring ototoxicity?

A
  • Baseline audio, tympanometry, DPOAEs (5-8 frequencies/octave) up to highest test frequencies with 65/55 dB SPL
  • Monitor every week to two weeks during administration of drug
  • Monitor 1 week, 1 month, and 3 months after drug discontinuation
47
Q

What is the criteria for change in auditory status when monitoring ototoxicity?

A
  • 15 dB decrease for pure tone AC threshold at one frequency or 10 dB at two frequencies
  • Decrease in DPOAE amplitude exceeding 2 dB test-retest reliability
  • Replicate behavioral results within 24 hours
48
Q

Describe SIDS as it relates to OAEs.

A

-Children who succumbed to SIDS had reduced TEOAE SNR in the right ear but not the left ear

49
Q

Abnormal OAEs may be related to what central auditory processes?

A
  • Temporal integration
  • Gap detection
  • Hearing in noise
50
Q

Why might there be 2 mechanisms affecting OAEs in Meniere’s patients?

A
  • Most have abnormal OAEs

- 20-30% have normal, robust OAEs even with mild to moderate SNHL

51
Q

Why are OAEs uncommonly used in intraoperative monitoring?

A
  • High noise levels
  • Doing ABR in that ear
  • Tumor size not always linked to presence/absence of OAEs
52
Q

What structure is the final stage of the efferent system?

A
  • Olivocochlear bundle (OCB)

- Contains fibers form the LOC and MOC from each ear

53
Q

Compare LOC vs. MOC.

A
  • LOC: thin, unmyelinated, terminates on afferent dendrites

- MOC: thick, myelinated, terminates on OHCs

54
Q

What might be the function of OAE suppression?

A
  • Protection from noise exposure
  • Hearing in noise
  • Attention
  • Auditory training
55
Q

What are the protocols for OAE suppression?

A
  • Ipsilateral, contralateral, or bilateral
  • Ipsilateral/bilateral might interfere with generation of OAE stimulus
  • All 3 might elicit ARTs, which would affect OAE level
  • Contralateral has the smallest effect
  • Broadband noise elicits the greatest suppression effect ~65 dB SPL

HESP706 (5 decks)

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