Week 2: ECochG

Question 1

super brief history ECochG

Answer 1

• 1st evoked potential
• identified in 1930 by weaver and Bray
• used clinically in 1960

Question 2

cochlear microphonic: what type of current and where does it come from

Answer 2

• AC activity from the OHCs

- –mainly basal OHCs

Question 3

summating potential: what type of current and where does it come from

Answer 3

*DC mainly from the IHCs

Question 4

compound action potential: where does it come from

Answer 4

8th nerve fibers

Question 5

what type of stimulus is best for each CM, SP, and CAP

Answer 5

• CM= pure tones (no latency, begins with stimulus)
• SP= high freq tones (high rate and TB)
• CAP= clicks or TB
• –when using a click, the AP latency will be 1 ms

Question 6

best polarity to use with each kind of ECochG goal

Answer 6

• CM: condensation and rarefaction

* SP: alternating click

Question 7

masking with ECochG

Answer 7

• contra masking is unneccessary as activity picked up by the noninverting electrode ipsi to the stimulated ear comes entirely from the stimulated ear
• inserts have an interaural attenuation of about 70 dB meaning any sound getting to the contra ear is weak
• if for some reason you need to use masking use a white noise at no more than 30 dB effective masking

Question 8

what is CAP best recorded with in EcochG

Answer 8

• click or TB, tones with animals?

- –analysis window must be bigger for TB than for click

Question 9

electrode placement sites for EcochG

Answer 9

• TM
• promontory or round window
• on the 8th nerve (intraoperative monitoring)

Question 10

recording using transtympanic electrodes

Answer 10

• near the cochlea is the non-inverting
• reliable responses
• small CM and SP
• still need 2 surface electrodes= another channel for the reference which is Fz meaning mid forehead and common ground which is Fpz which is the nasion

Question 11

difference between near-field recording and far-field ecochg recording

Answer 11

• near-field= promontory or round window and SP and AP amplitude are larger for round window
• far field recording is TM and the SP is small
• –this means you cant compare results from different electrode locations

Question 12

how to record negative waves for AP (N1)

Answer 12

*non-inverting (+) electrode close to the cochlea and *inverting (-) on the Cz/Fz/Fpz

Question 13

how to record positive voltage for AP

Answer 13

• non-inverting on the vertex or forehead

* inverting near the mastoid/TM/promontory

Question 14

analysis window for ecochg

Answer 14

• 5ms analysis window would contain CM, SP, and AP as all are complete by 5 ms
• 10 ms is preferable because it allows to record ABR simultaneously to check for PAM and is good with TB because they have extended durations and thus requires a longer window

Question 15

gain of ecochg

Answer 15

75000 or less

Question 16

filter settings for ecochg

Answer 16

*clicks: 100-3000 Hz like for ABR
—actually want a lower cut off at or below 50 Hz according to Hall
*TB: since SP contains energy in the range under 100 Hz
want a lower cutoff like 3-3000 for a better response

Question 17

how is the AP or N1 amplitude measured

Answer 17

from the baseline to the most negative peak

—SP is the hump on the leading slope of the AP

Question 18

SP/AP amplitude ratio for menieres

Answer 18

• ratio = 0.42-0.45
• –0.25 is the normal and 0.45 is the cutoff of what is normal since it is about 2 standard deviations form the mean
• large amplitude ratio has better sensitivity than the individual potentials
• –over all low sensitivity with 62% but high specificity with 95%

Question 19

AP width/duration in menieres

Answer 19

• 0.957 ms is the normal for subjects
• is prolonged in 2/3 of patients with menieres
• –1.327 ms for the affected ear and 1.158 ms for the nonaffected ear shows that those with menieres on one side have prolonged width on the other which indicated disease beginning in the normal ear as well

Question 20

SP/AP area ratio and menieres

Answer 20

• <1.94
• is measured from baseline to base
• anything above this value is abnormal
• large ratio has low sensitivity with 43.9%

Question 21

SP with a TB stimulus

Answer 21

will not look as nice as with click

Question 22

trouble shooting reduces ecochg with normal ears

Answer 22

• small or no AP & SP response, possibly due to recording or stimulus technique, so:
• –increase stimulus intensity
• –decrease stimulus rate
• –recording electrode closer to cochlea

Question 23

factors that may influence the outcome of AER recording in any subject, even persons with normal peripheral and central auditory system status

Answer 23

• age
• gender
• body temp
• state of arousal
• attention (not really ecochg)
• possible effects of drugs

Question 24

age effects on ecochg

Answer 24

• mature cochlea in newborn
• Ecochg is essentially mature at term birth
• CM and SP can be recorded in preterm newborns
• AP (N1) component as early as 27 weeks CA
• –longer in latency and reduced in amplitude compared to adult response
• ecochg is invasive in infants and children
• with advancing age: AP amplitude is diminished more than SP amplitude
• there is little demand for echochg for threshold estimation
• –with transtympanic recordings threshold may be within +/- 10 dB

Question 25

gender effect on ecochg

Answer 25

* no significant difference between male vs female for detectability of the SP - --Females: SP and AP amplitude is larger - -----not the SP/AP ratio is equivalent between the sexes

Question 26

body temperature effect on ecochg

Answer 26

* hypothermia: - --CM amplitude is reduced but no change in latency - --AP amplitude is reduced and latency is increased - --SP has variable changes * this could be seen in the OR

Question 27

attention and state of arousal on ECochG

Answer 27

* encourage sleep during recording of shorter latency responses because muscular and movement artifact will reduce the SNR * awake vs natural sleep has no differences in EcochG

Question 28

drug effects of ecochg

Answer 28

*minimal/negligible effect on EcochG

Question 29

4 disorders EcochG can be used to differentiate

Answer 29

* menieres disease * Ramsay Hunt syndrome * Lyme disease * acoustic neuroma - --note that for menieres latency is not important

Question 30

why is there an enhanced SP with endoloympatic hydrops?

Answer 30

* normally, the asymmetry in the vibration of the BM produces the SP * hydrops affects the elasticity of the BM - --increased endolymphatic (intralabyrinthine) pressure - --alters mechnaical properties of the cochlea - --greater vibratory asymmetry - --larger SP and abnormal SP/AP ratio

Question 31

senstivity of ECochG with both SP/AP area and ratio

Answer 31

92%

Question 32

CM with ANSD

Answer 32

will affect the AP and wave 1 of the ABR but not the CM so you will see a domination of the CM

Question 33

ECochG to monitor effectiveness of treatment

Answer 33

* record before, during and after: - --surgical treatment (endolymphatic sac decompression) or - --medical (glycerol or mannitol) therapy for menieres disease * can document the effectiveness of treatment by a decrease or normalize SP/AP ratio

Question 34

ecochg or ABR during vestibular neurectomy

Answer 34

*preservation of all components throughout surgery=preservation of the cochlear nerve

Question 35

Ecochg and ABR wave 1 relationship

Answer 35

the AP is also ABR wave 1 * to enhance the detection of ABR wave 1 with HF HL so that you can measure the latency between wave I-III and I-V can use ecochg * importance is for clinically and for interoperative monitoring of the cochlear and VIII activity during surgery