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60 Cards in this Set

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goal of electrode placement and type
consistently record a clear, complete, and sufficiently large EP
effect of electrodes on EP
may alter latency, amp, polarity, morphology of EP components
two types of electrode recordings
monopolar=one electrode in a pair is located far enough from generator to be inactive (incapable of detecting response)
bipolar=resposne conducted by both electrodes in pair
what are electrodes arranged in
a montage
noninverting electrode
where electrical activity is detected when connected to an amplifier or an evoked response system

does not undergo polarity reversal=just makes it larger
inverting
reference
undergoes polarity reversal
ground
used for reduction of electrical interference and artifact, used to get optimal response to ensure high quality recordings
types of electrodes (list)
dis type **
disposable electrodes
tiptrode (combo of electrode and insert phone)
interelectrode impedance
opposition to alternating current flow between one electrode and another
how is inter electrode impedance measured
with commercially available equip=small electrical current applied automatically to one electrode and amy of current reaching 2nd electtode is determined
max desierable interelectrode impedance
500 ohms; 5K
what should you aim for for inter electrode impedance
balanced and low (balanced=1-2 ohms)
what can you do if no balanced
1. reapply electrode (rescrub)
2. press on electrode for several moments
3. move electrode slightly
4. add more conducting pass
5. secure electrode with additional paste
10-20 international electrode system

odd vs. even

z
F
C
P
O
T
A
M
Fz
fpz-
odd=left
event=right

z-midline
F-frontal
C-coronal
P-parietal
O -occipital
T-temporal
A-earlode
M-mastoid
Fz-high forehead
fpz- unibrow
typical montage for ABR
noninverting electrode=Cz or Fz
inverting electrode=mastoid or earlobe
ground=opposite ear or mastoid t
how do we distinguish what is evoked from noise?
2 electrodes on diff places will detect same amount of electrical interference which is common to each electrode then
-differential preamp reverese polarity of input and subtracts input of noninvertiing =
common mode rejection ratio
measure of ability of preamp to reject similar activity at both inputs
-ratio of amp output when sig is presented to only one input relative to output when same sig is presented to both inputs

-varies w/ fq and electrode impedance
artifact rejection
based on sensitivity setting of amp, any sig detected by electrodes that excessed a disgnated present voltage is not sent to sig averaged (erase time period from memory)
filtering
objective to suppress preferentially those fq components of activity that contain particularly high amount of noise and energy

can effect amp and phase of input fq components
ideal filter
pass some input fqs (pass band) and totally suppress other fqs (stop band)
high pass filter
reject lower fqs and pass higher fqs

5-500 Hz
bandpass
rejects energy below a certain cutoff and above a certain cutoff=passing energy between 2 limits

100-15, 1500-3000
low pass filter
1000-8000 Hz
effects of high pass pilfering
as cutoff fq increases=amp reduces by about 50% and the latency progressively decreases
effects of low pass filtering
a decrease cutoff fq from 10000-300 Hz eliminates noise and enhances waveform analysis
dangers of filtering
remove important portions of response

waveform may consist of low/high fq components that will be affected differently by same filter
waveform analysis (list)
AEP waveforms
morphology
latency
amplitude
polaritiy
repeatiblity
AEP waveforms
sequence of peaks and valleys occurring w/in specific time period
Morphology of waveform
pattern of overall shape of waves, described w/ reference with expected norm (subjective parameter)
latency
time interval btwn exact moment of stim presentation and appearance of a change (peak or valley) msec
amplitude
microvolts

peak to following valley
polaritiey
direction, which way is up

depends on electrode location relative to generator of response and which electrode is plugged into positive and neg voltage inputs of differential amps
response reliability
two or more averaged waveforms where overlaid are very similar
factors affecting repeatablitiy
pt movement
muscle acitivity
identifying waves
clearly larger in amplitude than background noise
approximate latencies
I: 1/2 ms
II: 3/4 ms
V: 6/6 ms
interwave latency values
I-III: 2 ms
III-V: 2 ms
I-V: 4 ms
Wave V/I ratio
adult expect 2:1
child expect 1:1
extra peaks
OK

related to vertex-to-ipsi mastoid electrode array

most prominent in newborns
bifid wave I
wave I has 2 closes spaced peaks
not the end of the world
most common fused peak
IV/V
fusion of wave IV and V
more likely in cochlear path than normal ears
abnormal patterns
almost no limit

age and gender have effect
stimulus parameters (list)
frequency
duration
intensity
rate
polarity
mode of transduction
mode of stim presentation
masking
frequency of stim depnds on
stim intensity
EAA properties of transfused
ear canal and ME properties affecting sound transmission
integrity of cochlea

-\
what is the relationship between duration of response and duration of stim
direct
methods for fq specific ABR
mask fq regions not intended to be part of stim
-response to stim derived from other sources (method of subtraction)
-use of tonal stim
notched noise masking of stim

advantage
disadvantage
ad: no more time to record than tonal stim
dis: spread of low-fq component of masker into notch, broad small amp and sometimes indistinct morph of V
extra peaks
tone burst stimulus
permits fq specific ABR simply quickly and w/ relatively inexpensive instrumentation
duration
sum of rise time, plateau time, fall time
stim intensity
latency decreases and amp increases as intisity increases (expected but not always)
what happens to a template at a higher fq
skinner b.c less variability throughout the highs
ISI
interstim interval

interval btwn sucessess stim
rate
number stim per sec
what rate has little effect on ABR
up to 20/sec
why rate effects
cumulative neural fatigue and adaption and incomplete recovery

-rate effects slow and fast component
polaritiy: condensation
stim on produced by movmeem transducer diaphragm toward TM ((+) pressure wave)
polaritiy:rarefraction
pressure wave in (-) direction produced by moment of transducer diaphragm away from TM
polarity alternating
swathing between condensation and rarefaction
masking
present masking noise to nontest ear to attempt to ensure test ear is actually contributer

-just put 50 dB nHE in the other ear!!!