Week 2: ECochG Flashcards
super brief history ECochG
- 1st evoked potential
- identified in 1930 by weaver and Bray
- used clinically in 1960
cochlear microphonic: what type of current and where does it come from
- AC activity from the OHCs
- –mainly basal OHCs
summating potential: what type of current and where does it come from
*DC mainly from the IHCs
compound action potential: where does it come from
8th nerve fibers
what type of stimulus is best for each CM, SP, and CAP
- 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
best polarity to use with each kind of ECochG goal
- CM: condensation and rarefaction
* SP: alternating click
masking with ECochG
- 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
what is CAP best recorded with in EcochG
- click or TB, tones with animals?
- –analysis window must be bigger for TB than for click
electrode placement sites for EcochG
- TM
- promontory or round window
- on the 8th nerve (intraoperative monitoring)
recording using transtympanic electrodes
- 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
difference between near-field recording and far-field ecochg recording
- 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
how to record negative waves for AP (N1)
*non-inverting (+) electrode close to the cochlea and *inverting (-) on the Cz/Fz/Fpz
how to record positive voltage for AP
- non-inverting on the vertex or forehead
* inverting near the mastoid/TM/promontory
analysis window for ecochg
- 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
gain of ecochg
75000 or less
filter settings for ecochg
*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
how is the AP or N1 amplitude measured
from the baseline to the most negative peak
—SP is the hump on the leading slope of the AP
SP/AP amplitude ratio for menieres
- 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%
AP width/duration in menieres
- 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
SP/AP area ratio and menieres
- <1.94
- is measured from baseline to base
- anything above this value is abnormal
- large ratio has low sensitivity with 43.9%
SP with a TB stimulus
will not look as nice as with click
trouble shooting reduces ecochg with normal ears
- 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
factors that may influence the outcome of AER recording in any subject, even persons with normal peripheral and central auditory system status
- age
- gender
- body temp
- state of arousal
- attention (not really ecochg)
- possible effects of drugs
age effects on ecochg
- 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
gender effect on ecochg
- 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
body temperature effect on ecochg
- 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
attention and state of arousal on ECochG
- 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
drug effects of ecochg
*minimal/negligible effect on EcochG
4 disorders EcochG can be used to differentiate
- menieres disease
- Ramsay Hunt syndrome
- Lyme disease
- acoustic neuroma
- –note that for menieres latency is not important
why is there an enhanced SP with endoloympatic hydrops?
- 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
senstivity of ECochG with both SP/AP area and ratio
92%
CM with ANSD
will affect the AP and wave 1 of the ABR but not the CM so you will see a domination of the CM
ECochG to monitor effectiveness of treatment
- 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
ecochg or ABR during vestibular neurectomy
*preservation of all components throughout surgery=preservation of the cochlear nerve
Ecochg and ABR wave 1 relationship
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
