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Electrophysiology > Electrocochleography > Flashcards

Electrocochleography Flashcards

1
Q

What is ECochG?

A

a method for recording the electrical potentials that arise from the cochlea

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2
Q

What are the 3 components of ECochG?

A
  • summating potential
  • action potential
  • cochlear microphonic
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3
Q

From what structure does the SP arise?

A

from the cochlea, specifically the inner hair cells

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4
Q

From what structure does the AP arise?

A

from the auditory nerve

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5
Q

What types of electrodes are used during ECochG?

A

transtympanic, and extratympanic

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6
Q

Transtympanic electrode description

A

goes through the TM onto the cochlear promontory or the round window

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7
Q

Extratympanic electrode description

A

electrode stays within the ear canal

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8
Q

What type of stimulus is used to evoke ECochG?

A

clicks

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9
Q

Found on slide 4, what do TTracings display?

A

responses to rarefaction (R) and condensation (C) polarity clicks

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10
Q

The adding of separate R and C responses (middle tracing) enhances what?

A

the SP and AP

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11
Q

The subtracting of separate R and C responses (bottom tracing) enhances what?

A

the cochlear microphonic

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12
Q

What type of stimulus are AP and SP evoked by?

A

a stimulus of alternating polarity (a mix of condensation and rarefaction)

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13
Q

What type of of stimulus is the CM evoked by?

A

either a condensation or a rarefaction stimulus

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14
Q

How were the earliest ECochG measurements taken?

A

on patients undergoing ME surgery, or through a non-surgical approach involving a transtympanic electrode

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15
Q

What are the most popular applications of ECochG?

A

-diagnosis/assessment/monitoring of Ménière’s disease and endolymphatic hydrops
- assessment/monitoring of treatment for the above conditions
- enhancement of wave I of ABR
- intraoperative monitoring of cochlear and auditory nerves
- diagnosis of auditory neuropathy

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16
Q

CM characteristics

A
  • no latency
  • most effectively elicited by single polarity stimuli
  • arises from the outer hair cells
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17
Q

SP characteristics

A
  • arises from the inner hair cells
  • reflects the extracellular activity of hair cells during acoustic stimulation
  • a direct current distortion potential
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18
Q

AP characteristics

A
  • arises from the afferent cochlear nerve fibers as they enter the habenula perforata
  • represents the synchronous firing of the auditory nerve fibers
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19
Q

The SP/AP amplitude or area ratio is used to determine what?

A

if the ECochG results are normal or abnormal

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20
Q

The TIPTrode serves as both an … and a …?

A

electrode, and stimulus deliverer

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21
Q

What is the general procedure for placing TIPTrodes?

A
  • perform otoscopy to ensure no cerumen or dirt and debris are present
  • scrub the ear canal with Nu-prep on a Q-tip
  • easily squish the gold foil insert and place it into the ear
  • make sure the black tubing on the insert is flush with the ear canal entrance
  • attach the alligator clip to where it touches the foil on the black tubing
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22
Q

What are the testing parameters for ECochG?

A
  • a loud stimulus of at least 90 dB (can be detected as low as 60 dB)
  • use an insert transducer
  • use an alternating polarity stimulus, click, with 100k gain
  • set high and low pass filters at 10 - 500 Hz, with the artifact filter on
  • 5-10 msec time window
  • at least 2,000 sweeps
  • have an acquisition delay of -1, so there will be a small time before the stimulus onset
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23
Q

What is the general goal of ECochG?

A

to look for a difference between the SP and the AP

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24
Q

When using ECochG, what type of stimulus would we NOT use for diagnosis of ANSD?

A

an alternating polarity stimulus

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25
Q

Which is the first component of the ECochG waveform?

A

the cochlear microphonic

26
Q

The cochlear microphonic is a…

A

stimulus-dependent cochlear response, which changes direction with the changing polarity

27
Q

Which component of ECochG will not be visible if an alternating click stimulus is used?

A

the cochlear microphonic

28
Q

The SP can be seen as a … on the AP or Wave I.

A

leading hump (although it can appear as a completely separate hump)

29
Q

The last component to look for on the ECochG waveform is the what?

A
  • the AP (which is the same as Wave I on the ABR)
  • an alternating current response generated by the cochlear end of the VIIIth nerve
30
Q

What are the norms for ECochG responses obtained with TIPTrodes?

A
  • SP/AP amplitude ratio of less than 50% is within normal limits (0.5)
  • SP/AP area ratio of less than 35% is within normal limits (0.35)
31
Q

What is the most common electrode montage used for ECochG?

A

left ear = TIPTrode
right ear = TIPTrode
high forehead = electrode
low forehead = ground electrode

32
Q

What is the procedure for setting up the electrode montage?

A
  1. clean electrode sites with an alcohol wipe
  2. exfoliate skin with Nu-Prep; wipe off excess solution
  3. apply conductive paste to reusable electrodes (disposable electrodes are ready to apply on skin)
  4. apply electrodes and secure with tape
33
Q

Cochlear microphonic characteristics

A
  • alternating current response that mirrors the stimulus’ waveform (at low-moderate levels of stimulation)
  • arises from the OHCs in the Organ of Corti
  • its phase and duration are stimulus dependent
  • inhibited in response to alternating polarity stimuli
34
Q

How can cochlear microphonic recordings be applied in clinical scenarios?

A

It has received recent attention in the diagnosis of ANSD; other inner ear/auditory nerve disorders hasn’t been established yet.

35
Q

The SP is dependent on …., and tends to be obscured by…

A

the duration of the stimulus; the CM of stimulus artifact when recorded in response to stimuli presented in condensation or rarefaction polarity

36
Q

Some components of the SP are thought to represent what?

A

the sum of various nonlinearities associated with transduction processes within the cochlea

37
Q

What does the magnitude of the SP represent?

A

a reflection of the amount of distortion that accompanies or is produced by the transductive processes of the cochlea (this makes the SP useful for certain clinical scenarios)

38
Q

An enlarged SP value is indicative of what?

A

Ménière’s disease and/or end-lymphatic hydrops (this is because the amount of distortion associated with the transduction process increases as an effect of the condition)

39
Q

When does the AP occur?

A

at the onset of the stimulus (even for tone bursts)

40
Q

What is the AP characterized by?

A

brief, typically negative peaks; independent of stimulus phase and duration

41
Q

The magnitude of the AP relates to…?

A

the reflection of the number of nerve fibers firing

42
Q

The latency of the AP represents what?

A

the time between the stimulus onset and the peak of N1 (this is analogous to the “absolute latency” for ABR components)

43
Q

What is the most popular application of the AP in clinical situations?

A

the measurement of its magnitude in comparison to the SP in patients suspected of having Ménière’s disease and/or end-lymphatic hydrops

44
Q

An enlarged SP/AP amplitude ratio is indicative of what?

A

end-lymphatic hydrops

45
Q

What is the primary advantage of using a TT electrode for ECochG?

A
  • it obtains a very close proximity to the structures that generate the response, thus it gives a favorable SNR
  • essentially, we can get large readings without as much signal averaging
46
Q

What is a main disadvantage of using a TT electrode for ECochG?

A

it’s invasive and require’s a physician’s assistance, and it can be painful even with local anesthetic

47
Q

What is a main disadvantage of using ET electrodes during ECochG?

A

obtained responses require more signal averaging, thus the recorded components tend to be smaller in amplitude that their TT electrode counterparts

48
Q

What is a main advantage of using ET electrodes during ECochG?

A

they are generally painless, and can be used by audiologists in non-medical settings (no need for sedation/local anesthesia)

49
Q

When do ECochG components generally occur on the waveform?

A

within 10msec (latency) of the stimulus’ onset; thus they’re considered to be “early” or “short-latency” AEPs

50
Q

Which recording electrode is designed for placement on the TM? (hint: this placement ensures the AP displays as negative on the waveform)

A

the primary/non-inverting (+) electrode

51
Q

What is the most popular stimulus to evoke short-latency AEPs?

A

broadband clicks, BECAUSE they excite synchronous discharge from a large amount of neurons (this produces well-defined components in the recording)

52
Q

What is the most popular duration of the click stimulus to use during ECochG?

A

100 microseconds

53
Q

Which comparison measure do most professionals use when assessing possible pathological causes of abnormal ECochG results?

A

the amplitude measure (the height of the SP vs AP)

54
Q

How do you compute the SP/AP amplitude ratio?

A

SP/AP x 100 to get a percentage (typically the software will do the math for you)

55
Q

Normative data for ECochG depends on what variable during testing?

A

the type of electrode used (TIPTrode vs tymptrode)

56
Q

What are the common accepted norms for the SP/AP amplitude ratio for both electrode types?

A

TIPTrode = >50%
Tymptrode = >25%

57
Q

In simple terms, normal ears have a … SP/AP amplitude ratio, while “diseased” ears have a … SP/AP amplitude ratio.

A

larger; smaller

58
Q

What is the reported incidence rate for the presence of enlarged SP and SP/AP amplitude ratios in patients with Ménière’s disease?

A

approximately 60-65%

59
Q

What other condition has presented with enlarged SP/AP amplitude ratios?

A

perilymphatic fistulae

60
Q

How is the use of ECochG helpful for intraoperative monitoring?

A
  • avoiding potential trauma to the nerve (can preserve hearing)
  • identifying anatomical landmarks, such as the endolymphatic sac
  • help predict post-operative outcomes (especially for end-lymphatic decompression/shunt placement for Ménière’s disease/endolymphatic hydrops)
61
Q
A

Electrophysiology (5 decks)

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