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AUD fall 2019 electrophys I > Week 8: ECochG > Flashcards

Week 8: ECochG Flashcards

1
Q

what is ECochG

A

sound evoked cochlear and neural responses

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2
Q

what are the three parts of ECochG

A
  • cochlear microphonic
  • summating potential (SP)
  • action potential (AP)
  • –AP has N1 from the proximal auditory nerve and N2 from the distal auditory nerve
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3
Q

how long after the stimulus does ECochG occur

A

within 5 msec

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4
Q

what is the cochlear microphonic

A
  • mimics the stimulus
  • –sine wave of frequency of stimulus
  • is the alternating current (AC) arising from outer hair cells
  • –recorded response is mostly from the basal part of the cochlea
  • best evoked by frequency specific signals, and can be evoked using a click
  • latency does not change with intensity
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5
Q

what is the summating potential

A
  • direct current (DC) arising possible from the inner hair cells (has 0 frequency)
  • DC means doesnt change direction and therefore wont have frequency because cant measure alterations of the current
  • SP may be viewed as a shirt in the baseline of an ECochG recording
  • best recorded with higher frequency and can be evoked with click
  • is seen by averaging alternating stimulus because CM and SP happen at the same time so need to use alternating presentation to get rid of the CM
  • latency is not affected by intensity
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6
Q

what is the action potential

A
  • most commonly used is N1
  • –alternating current (AC) arising from the distal part of the VII nerve
  • ——-FFT response frequency up to 1000 Hz
  • –best recorded using click stimulus
  • –same as wave 1 of ABR
  • latency is a/b 1.5 ms
  • AP amplitude increases and latency decreases with increased stimulus intensity
  • less commonly used is N2
  • –it is wave II of the ABR response and behaves similar to N1
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7
Q

three electrode types and amplitudes of N1

A
  • TIPtrode N1 amp=0.1-1 microV
  • TM electrode N1 >1 micro V
  • trans-tympanic electrode Na amplityde= 15-25 micro V
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8
Q

electrode montage to record a negative voltage response

A
  • non-inverting electrode near the ear (mastoid, TM, or promontory)
  • inversting electrode on Cz/Fz/Fpz
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9
Q

electrode montage to record a positive voltage response

A
  • non-inverting electrode on Cz/Fz/Fpz

* inverting electrode near the ear (mastoid TM promontory)

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10
Q

best type of transducer for ECochG

A

inserts allow for easier recording using the different types of electrode and less artifact

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11
Q

stimulus for SP/AP recordings

A

click stimulus of 100 micro volts (specifically used for AP recordings)

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12
Q

stimulus for CM recordings

A

controls for artifact

*longer duration is needed for better CM and SP recording

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13
Q

stimulus rate effect on CM/SP/AP

A
  • doesnt affect SP or CM
  • affects SP because speeding the rate makes the nerve fatigue so amp decreases and latency shifts to longer
  • –use 7.1 or 9.1/second
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14
Q

stimulus polarity needed for SP/AP/CM

A
  • SP/Ap need alternating to get rid of CM

* CM recording use rarefaction and condensation

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15
Q

stimulus intensity affects on SP/AP/CM

A
  • as intensity increases, amplitude increases and latency decreases
  • as intensity increases SP raises in amplitude but latency stays the same
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16
Q

Epoch settings for SP/AP and CM

A
  • SP/AP is 5-10 msec
  • CM recording (SP)= extended window
  • –CM follows stimulus so if stim is 5 msec the response will be 5 msec
17
Q

filter settings for SP/AP and CM

A
  • SP/AP should be 10-3000Hz

* CM should be wide enough to include the frequency of interest

18
Q

amount of amplification a ECochG signal needs

A

75,000-100,000X

19
Q

what does electrode impedance need to be for ECochG

A

as low as possible and similar between the electrodes

20
Q

what are the three clinical applications of ECochG

A
  • CM helps with testing the cochlear function
  • enhances detection of wave 1 which is needed in diagnostic testing
  • SP/AP are useful for evaluating meniere’s disease
21
Q

how are SP/AP used to evaluate meniere’s

A

looking at the ratio between the amplitude of SP and AP

  • baseline (pre stimulus or at 0ms) ans then look at how far the SP is from baseline and how far the AP is from baseline
  • –abnormal if the ratio is bigger than 0.45 (the endolymph makes the SP larger
  • also use SP/AP area ratio
  • –w/ increased endolymph, SP becomes larger and wider
  • –abnormal if the ratio is larger than 2
22
Q

what is the sensitivity to menirers disease if using both the SP/AP amplitude and area ratios

A

92%

AUD fall 2019 electrophys I (11 decks)

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