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Diagnostic Audiology > Otoacoustic emissions > Flashcards

Otoacoustic emissions Flashcards

Auditory-evoked potential response (AEPR), transient-evoked and distortion product otoacoustic emissions (TEOAEs and DPOAEs)

1
Q

What are otoacoustic emissions?

A

Sounds which are generated within a normally functioning cochlea and recorded in the ear canal

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2
Q

Which are otoacoustic emissions the result of?

A

Normal outer hair cell non-linear processing

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3
Q

What are otoacoustic emissions used for in clinic?

A

To assess normal cochlear function using non-invasive, non-behavioural technique

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4
Q

What kind of mechanical properties does the cochlea have?

A

Both passive and active mechanical properties

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5
Q

Describe the passive element of cochlear mechanics

A

-Each point along the basilar membrane is tuned to a specific frequency (base- high frequency, apex- low frequency)
-When pressure waves enter the cochlea it causes vibration of the basilar membrane
-The vibration takes the form of a “travelling wave” which appears to travel from the base of the cochlea to the apex
-The wave peaks at the place tuned to the frequency of sound and then dies away rapidly
-These passive mechanical properties are not sufficient to provide the sensitivity and frequency tuning observed in mammalian hearing

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6
Q

Describe active cochlear mechanics

A

-Cochlear amplifier
-Positive feedback loop within cochlea amplifies the travelling wave
-Vibrations within the organ of Corti are sensed and then force is generated in synchrony to increase the vibrations

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7
Q

What does the cochlear amplifier add?

A
  1. Gain
  2. Dynamic range
  3. Sharpens mechanical frequency tuning close to the peak of the travelling wave
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8
Q

What is thought to be the origin of otoacoustic emissions?

A

-Outer hair cell electromotility
-Outer hair cells change length in response to electrical stimulation when synchronized
-Any lack of uniformity in the OHC movements will lead to instability of the system which causes amplified energy to scatter back to the base of the cochlea, through the middle ear and into the ear canal where it appears as sound (otoacoustic emission)

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9
Q

What are the two broad types of otoacoustic emissions?

A
  1. Non-evoked otoacoustic emissions
  2. Evoked otoacoustic emissions
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10
Q

What is another name for non-evoked otoacoustic emissions?

A

Spontaneous otoacoustic emissions

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11
Q

What are the three types of evoked otoacoustic emissions?

A
  1. Transient Evoked otoacoustic emissions (TEOAEs)
  2. Distortion Product otoacoustic emissions (DPOAEs)
  3. Stimulus Frequency otoacoustic emissions (SFOAEs)
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12
Q

When do spontaneous OAEs occur?

A

They are measured in the absence of any external stimulation

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13
Q

What proportion of normally hearing individuals exhibit spontaneous OAEs?

A

Around 30-60% of normally hearing adults and 25-80% of normally hearing neonates (40-50% of normally hearing subjects)

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14
Q

At which level of hearing loss can spontaneous OAEs no longer be recorded?

A

When thresholds exceed 30 dB HL (mild hearing loss or greater)

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15
Q

Do spontaneous OAEs have any clinical applications?

A

Presence of spontaneous OAEs are a signal of cochlear health but absence is not a sign of abnormality necessarily so they do not have a lot of clinical utility

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16
Q

At which frequency region and amplitudes do spontaneous OAEs usually occur for humans?

A

Frequency: 1-2 kHz
Amplitudes: 5-15 dB SPL

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17
Q

How many spontaneous OAEs were measured in this normally hearing individual?

A

Three at 1.025 Hz, 1.4 kHz and 1.8 kHz

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18
Q

What are transient evoked OAEs (TEOAEs)?

A

-OAEs recorded in response to very short or transient stimuli e.g. click or tone burst
-Presence of a TEOAE suggests hearing sensitivity (no greater than a mild hearing loss)

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19
Q

Why are the first 2.5-4 seconds of the TEAOE recording eliminated from the final waveform?

A

It contains the stimulus click so we would be recording the stimulus rather than the response to the stimulus

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20
Q

Why is the TEAOE response averaged?

A

In order to decrease the noise in the trace as the response is very small and very quiet

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21
Q

How many sweeps are generally performed for a TEAOE? Why?

A

-260 sweeps- stimulus is played 260 times and the response is measured 260 times
-This appears to be the ideal number to get a good signal without taking too much time

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22
Q

What three factors are used to determine whether a TEAOE is present?

A
  1. Amplitude: Minimum 0 dB SPL
  2. SNR score: 6 dB or more at 2 or more half-octave bands between 1.5-4 kHz
  3. % reproducibility: 70% of greater overall and in minimum 2-3 frequencies
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23
Q

What is the shape of the waveform dependent on?

A

Several factors including the evoking stimulus and the recording parameters

24
Q

Is a TEAOE present in this trace?

A

-Can see the response in blue rising from the noise (in red)
-Overal reproducibility over 98%
-SNR is 6 dB or more at 2 or more half octave bands
-Response present

25
Q

Is a TEAOE present in this trace?

A

-Not a lot of response rising from the noise
-Reproducibility only 63%
-SNR does not reach 6 dB at any frequencies
-No response/ small response

26
Q

Is a response present in these TEAOE traces?

A

-Strong waveform on the left
-Reproducibility is 98% in both ears
-Amplitude needs to be above 0 dB SPL and at 4 kHz it is under 0 for both ears (not a clear response)
-SNR score is greater than 6 dB across the range of frequencies
-Overall the response is present but could be stronger (lack of amplitude at 4 kHz)

27
Q

What are distortion product OAEs (DPOAE)?

A

OAEs recorded following stimulation with two simultaneous pure-tones of different frequencies

28
Q

In DPOAEs, is f1 or f2 greater?

A

f1 is greater than f2

29
Q

What are the names of the levels that f1 and f2 are presented at?

A

L1 and L2

30
Q

How far apart in frequency are f1 and f2?

A

They are reasonably close in frequency

31
Q

What does the interaction of the two frequencies on the basilar membrane cause?

A

-Generation of energy at other discrete frequencies which can then be measured
-These frequencies are arithmetically related to the primary frequencies

32
Q

What equation yields the highest amplitude in humans?

A

2f1- f2

33
Q

Which characteristics of the primary tones cause variations in response levels?

A

-Frequency
-Frequency separation
-Level separation
-Overall level

34
Q

How does frequency separation affect response level?

A

-The largest response in humans is obtained with f2/f1 ratio of 1.22 (i.e. f2 is 1.22 x f1)
-The further apart the primary frequencies are from each other the less the interaction of their respective travelling waves on the basilar membrane

35
Q

How does the overall level affect the response level?

A

-L1 needs to be greater (louder) than L2 for largest response
-Usually use 65 (L1)/ 55 dB (L2)

36
Q

From this DPOAE recording, state what the frequencies of f1 and f2 are, and what levels they were presented at

A

-L1 is 65 dB, L2 is 55 dB
-Frequency of f1 is 850 Hz and the frequency of f2 is almost 1 kHz
-Measure the 2f1- f2 plot at the fixed f2 frequency

37
Q

What does the grey area represent? What determines which category of DPOAE presence/ absence the response falls into?

A

-The grey area represents the range for normally-hearing people
-Depending on the amplitude of response the responses fall into the different categories (present and within normal range, present but abnormal etc)

38
Q

At which PTA thresholds are DPOAEs expected to be present?

A

-When PTA thresholds are better than 25 dB HL
-However can still be recorded in individuals with mild-moderate (40-50 dB HL) SNHL where TEOAEs are absent

39
Q

What are the limitations of DPOAEs?

A

-Ambient low-frequency noise overlaps the 2f1-f2 response
-Reliability is greatest at frequencies greater than 1 kHz
-Calibration at high frequencies is difficult due to standing waves and transducer quality

40
Q

What are stimulus frequency OAEs (SFOAEs)?

A

-Occur at the same frequency and the same time as a continuous pure tone applied to the ear
-Require specialist equipment to extract the SFOAE from the evoking stimulus

41
Q

Are SFOAEs able to be used in clinical practice?

A

No because they require specialist equipment and there is a lack of availability of commercial devices

42
Q

Why are SFOAEs useful and what are they used for?

A

-SFOAEs are most frequency specific in probing functional status of the cochlea compared to the other types of OAEs
-Used mostly in research to investigate cochlear tuning and function of the efferent auditory system

43
Q

What are the main differences between TEOAEs and DPOAEs?

A

-TEOAEs and DPOAEs allow us to look at cochlear function in different ways
-Absent TEAOEs are recorded for hearing loss greater than 20-30 dB but DPOAEs will still be present until a hearing loss greater than 40-50 dB is present
-TEOAEs use a broadband click stimulus whereas DPOAEs are frequency specific (f1 and f2)
-TEOAEs are more useful for lower frequency range (0.5- 4/5 kHz) and DPOAEs are more useful for higher frequency range (1-8/ 16 kHz)
-TEOAEs are related to the electromotility of the OHCs whereas DPOAEs demonstrate the non-linearity of OHC physiology (e.g. transduction)

44
Q

What are the prerequisites (prior condition) for recording OAEs?

A

-Unobstructed external ear canal (allows evoking stimulus to travel through the outer and middle ear into the cochlea)
-Absence of middle ear pathology (OAE needs to travel out into the ear canal without the energy being significantly reduced and becoming too small to measure)
-Optimal positioning of the OAE probe
-Ability to seal the ear canal with the probe
-Relatively quiet conditions

45
Q

What are the applications of otoacoustic emission measurement?

A
  1. Screening- neonatal, preschool and school-aged children, occupational health
  2. Monitoring- ototoxicity, noise-induced hearing loss
  3. Diagnostic- sensory vs neural hearing loss, non organic hearing loss, in non-cooperative patients
46
Q

What are otoacoustic emissions not able to measure?

A

Frequency specific hearing sensitivity

47
Q

Why are TEAOEs used for newborn hearing screening?

A

-Small soft-tipped earpiece is played in the baby’s ear and gentle clicking sounds are played
-Recordable at birth and is a reliable and quick test of hearing function
-It is an easily interpreted test so does not need to be carried out by an audiologist
-Objective test so the baby does not need to respond

48
Q

Why are OAE useful for ototoxicity monitoring?

A

-OHCs are typically affected by ototoxic drugs which cause auditory/ vestibular dysfunction which is often permanent
-Measuring DPOAEs is more sensitive than conventional audiometric testing and appears to be sensitive to pre-clinical hearing loss (patient may not even have noticed any problems with their hearing)

49
Q

What is the advantage of monitoring ototoxicity?

A

-Provides opportunities for audiologists to counsel patients and their families regarding ototoxicity- induced hearing loss, tinnitus, dizziness and introduce communication strategies
-It also provides audiologists with the opportunity to provide appropriate rehabilitation during and after treatment or a change in the drug regime

50
Q

How are OAEs helpful in distinguishing sensory vs neural hearing loss?

A

-In auditory neuropathy spectrum there is evidence of OHC function
-Caused by poor conduction of the signal along the auditory nerve
-Discrepancy between PTA results and speech perception abilities
-The presence/ absence of the OAE is an important part of diagnosis

51
Q

What kind of OAE is observed here? Is it present or absent and why?

A

-Transient evoked OAE (TEOAE)
-Present
-Amplitude- 19.3 dB (more than 0), reproducibility (99%)- more than 70% and SNR scores more than 6 dB for 2,3 and 4 kHz

52
Q

What kind of OAE is observed here? Is it present or absent and why?

A

-Transient evoked OAE (TEOAE)
-Present
-Amplitude greater than 0 dB (5.6 dB), reproducibility- 81.5%, 2 SNR scores more than 6 (2 and 3 kHz- 11)

53
Q

What kind of OAE is observed here? Is it present or absent and why?

A

-Transient evoked OAE (TEOAE)
-Absent but make a note and cross check with other tests because there is some function of outer hair cells
-Reproducibility okay- 96%, amplitude okay- 14 dB, but only one SNR score exceeding 6 (8- 2kHz)

54
Q

What kind of OAE is observed here? Is it present or absent and why?

A

-Distortion product OAE (DPOAE)
-Present
-All points within or above the 5th-95th percentile, no points within noise floor

55
Q

What kind of OAE is observed here? Is it present or absent and why?

A

-Transient evoked OAE (TEOAE)
-Present
-Signal above 0 dB for each frequency, reproducibility likely to be high because waveforms overlap, SNR score more than 6 for all frequencies

56
Q

What kind of OAE is observed here? Is it present or absent and why?

A

-Transient evoked OAE (TEOAE)
-Present in the right ear (although the amplitude smaller than 0 at 1 kHz)
-Response absent in the left ear (No response (blue) rising out of the noise (blue), SNR not more than 6 dB at more than 2 half octaves, amplitude not exceeding 0 dB)

57
Q

What kind of OAE is observed here? Is it present or absent and why?

A

-Transient evoked OAE (TEOAE)
-Present otoacoustic emissions
-SNR greater than 6 dB for all recorded frequencies, amplitude greater than 0 dB for all frequencies except 4 kHz
-Reproducibility value not present but can see the waveforms overlapping so it is likely high

Diagnostic Audiology (12 decks)

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