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AUD spring 2020 Electrophys II > Week 4 and 5: ABR > Flashcards

Week 4 and 5: ABR Flashcards

1
Q

where are early potentials generated

A
  • ecochg from the VIII nerve

* ABR from the VIII nerve and brainstem

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2
Q

where are middle potentials generated (AMLR)

A

temporal/thalamus

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3
Q

where are late potentials generated (LLR)

A

cortical

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4
Q

how are event-related potentials special

A

they are cortical and cognitive

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5
Q

are are steady-state responses generated

A

the brainstem-cortex

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6
Q

three other names for ABR

A
  • BSER= brainstem evoked response
  • BAER= brainstem auditory evoked response
  • BAEP= brainstem auditory evoked potential
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7
Q

what is the ABR

A

neurophysiological measure of auditory brainstem function in response to auditory stimuli

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8
Q

what is the objective of ABR

A

auditory assessment without the need of a voluntary response

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9
Q

how to measure ABR basic

A
  • a series of stimuli (clicks)
  • –presented to the ear at a constant rate by a transducer
  • –generates a response from the base of the cochlea
  • the signal travels along the auditory pathway from the VII nerve to the IC
  • the electrodes pick up the neural response, which is amplified, filtered and then averaged b a computer
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10
Q

ABR waves basic

A
  • the waveform peaks are labeled I-VII in a time-domain display
  • occur within a 10 ms after a click is presented, at high intensities (70-90 dB nHL)
  • normal variability exists between individuals
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11
Q

anatomical location of each wave of the ABR

A
  • I is the action potential of the distal VII nerve
  • 2 is the proximal VIII nerve and the cochlear nucleus
  • 3 is the lower pons (cochlear nucleus, SOC, and lateral lemniscus)
  • 4 mid/upper pons which is the SOC and lateral lemniscus
  • 5 is the lower midbrain or lateral lemniscus and inferior colliculus
  • –note the more proximal the more generators and thus the waves will get larger and larger, cannot really pinpoint the exact lesion with ABR because there are many generators to each wave so can reduce to the level but cant find super site specific
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12
Q

why are early potentials better than late potentials for evoked potential audiometry

A
  • recorded and replicable at all ages, even premie babies
  • recorded while pt is asleep or awake
  • not affected by sedatives
  • reliable and valid responses
  • originate from peripheral and central neural auditory structures
  • correlated with lesions of VII nerve, lower brainstem, or both
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13
Q

3 criteria to base interpretation of ABR off of

A
  • morphology of the waveforms
  • latency
  • amplitude
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14
Q

repeatability/reliability/ reproducibility/ replication

A
  • two recordings under the same stimulus conditions except for slight variations due to background noise
  • waveforms that are not repeatable should not be considered responses
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15
Q

ABR interpretation based on morphology

A
  • subjective appearance and shape of the waveform
  • 20% normals have different morphology between ears
  • possible variations in wave IV/V complex in normal people
  • abnormal morphology would be an absent response when expected to see one, one of the waves is missing, wave 5 is not the biggest, system dominated by CM
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16
Q

ABR interpretation based on latency

A
  • latency is the time between the onset of the stimulus presentation and the change in the waveform (peak or valley)
  • good, consistent measured of brainstem functioning
  • prolonged in newborns (reaching adult values by 18 months
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17
Q

three latency measures to look at with ABR

A
  • absolute latency- the time at which you record the peak of the wave
  • interpeak lantency intervals
  • interaural latency difference
  • –this is critical for retrocochlear pathology
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18
Q

how to pick the peak of an ABR wave

A
  • point on wave of greatest amplitude, but
  • –not best represent the save as in some IV/V complexes
  • –rounded top portion of wave
  • —–can mark the shoulder or peak of wave V, but must be consistent
  • chose final data point before negative slope shoulder but
  • –multiple shoulders
  • —–dont really mark the shoulder of any wave except for wave V
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19
Q

what is the interpeak latency

A
  • the intervals between two different waves
  • –I-III
  • –III-V
  • –I=V
  • aka IPL or IWL
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20
Q

what is central conduction time (CT)

A
  • the interpeak latency of waves I-V
  • I-V latency is around 4.0 ms
  • –a slow CT is an indicator of a retrocochlear pathology
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21
Q

what is the interaural latency difference (IL5)

A

*a comparison of wave V latencies between the 2 ears in retrocochlear disorders

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22
Q

what is the normal wave V latency in respect to presentation level

A

0.2ms decrease in latency with every 10 dB increase in intensity between 50-70 dB HL

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23
Q

what is the normal ILD of wave V

A

less than 0.4 ms

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24
Q

how does the increase of stimulus rate (RR) affect latency

A
  • V latency shifts < 0.6-0.8 ms

* greater shift with brainstem lesion

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25
Q

how to limit error in ABR interpretation in clinical practice

A
  • need a “normal” database
  • –can used published data if protocol is identical
  • all clinicians must adhere to established protocols and analysis data
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26
Q

interpreting ABR based off amplitude

A
  • amplitude is measured in microvolts
  • is the second major response parameter
  • is measured by difference in microvolts from the peak through the following trough or baseline to peak
  • –can use this to compare the amplitude ratio between wave I and V because wave 5 should be bigger
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27
Q

3 things the characteristics of recorded EPs depend on to some extent

A

1) the recording parameters
2) stimulus parameters
3) non-pathological subject variables
* all of these must be taken into consideration when interpreting

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28
Q

list of typical ABR recording parameters

A
  • Fz or Cz being noninverting
  • –really dont use Cz unless doing a late recording
  • A1/A2 being inverting
  • nasion/Fpz being ground
  • suggests 4 electrodes, 2 channels minimum
  • band-pass filter: 30 or 100-3000 Hz
  • amplification (gain): 100000-150000
  • sensitivity: 25 microvolts (not a setting on all equipment)
  • sampling points: 512
  • sweeps: 1024-2048 or more
  • transducer: insert or B70
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29
Q

in most instrumentation, ABR parameters are controlled by

A

directly controlled/adjusted by the audiologist

30
Q

what need/cause be immediate modification of acquisition factors during clinical measurement

A
  • changes in pts status
  • changes in test environment
  • information obtained from online analysis
31
Q

automated ABR

A

preprogrammed test protocols

32
Q

6 main recording parameters

A

1) 10-20 international electrode system
2) analysis window–recording epoch
3) filter setting
4) ipsilateral vs contralateral recording
5) sweeps and sampling number
6) transducers

33
Q

10-20 international electrode system

A
  • location of electrodes in relation to the cortex
  • 10-20 referes to the 10% or 20% inter-electrode distance
  • –the distance between Nz (nasion) and Oz (inion) is divided into 10% and 20% increments
  • 1st letter identifies brain lobe
  • numbers identify left or right (even is right and left is odd)
34
Q

4 big landmarks on the 10-20 system

A
  • nasion (Nz) the most anterior inferior site (the bridge of the nose)
  • inion (oz) the most posterior inferior site (occipital protruberance- lower back midline region of the head
  • Fp= frontoProximal
  • z= midline
35
Q

ABR electrode montage

A
  • noninverting (+) on Cz (vertex) or Fz (hairline)
  • inverting electrode (-) on earlobe (A) or mastoid ipsi to the stimulated ear
  • –A1/M1 for left A2/M2 for right
  • ground on Fpz or any iste
  • use two channel for ABR to be able to record ipsi and contra (not that for EcochG use single channel)
36
Q

single channel montage for ABR

A
  • record from the side of the head ipsi to the stimulated ear (Cz/Mi + ground)
  • Fz or Fpz to Ai(Mi) and
  • ground electrode is the contra ear (Ac/Mc)
  • advantage: one less electrode to apply and remove
  • –similar response to 2 channels, possible smaller peak amplitude
  • disadvantage: no ipsi and contra recordings
  • –binaural recording is impossible with 3 electrode montage
37
Q

analysis window or recording epoch in ABR

A
  • ABR provides replicable +/- peaks that occur between 0-10 ms poststimulus
  • 10 ms is not absolute though!
  • –need to consider application, circumstances and etc
  • –can be necessary to extend to 15 ms analysis window (or longer)
  • —–with threshold searching, may want to expand the window to 25 ms to be sure you can see the whole waveform when the latency is prolonged
38
Q

when to use a longer epcoh with ABR

A
  • longer being about 15+ ms
  • neonates= longer latency close to threshold
  • IOM= hypothermia leads to prolonged wave V
39
Q

when to use a shorter epoch with ABR

A
  • about 5 ms
  • really only use when recording ecochg aka when looking for the CM, SP, and whole nerve AP
  • –cannot use 5ms window with ABR or you will not see wave 5
40
Q

filter settings for ABR

A
  • 100-3000Hz is the recommended
  • –want to use over 2000Hz to sharpen the peak and have greater precision
  • 30-3000Hz is a good starting point if digital filtering is not available
  • —-note that the filter is a bandpass filter and the lower the high pass the better the resolution, if the roll off is too big it will add too much to the recording
  • EEG society recommends the high pass setting to be 10-30Hz
  • –this helps to assess auditory sensitivity in neonates and young infants
  • –more info about the underlying pathophysiologic process
  • –also recommends the low-pass filter set under 3000Hz as EP energy lies above 1000 Hz but you still want to eliminate some high freq energy/noise
  • high pass filter skirt/roll off 12 dB/ octave or less
41
Q

do you want to use more or less filtering?

A
  • filter as little as necessary
  • start with 30 or 100-3000 Hz and change as needed
  • try and do noise control instead of changing the filtering
  • –proper electrode placement is very important
  • –instrumental shielding and grounding
  • patient comfort should be ensured to minimize movement
42
Q

why record ipsi and contra ABR?

A
  • contra crosses at the level of the SOC, so you can record ipsi and contra simultaneously when using 2 channels and presenting to 1 ear
  • –contra separates wave 4 and 5 better
  • –contra are a little earlier because more neural representation for contra (about 0.1 ms earlier)
  • –know that ipsi and contra responses are similar when clicks are presented to one ear to elicit EPs from both sides of the head
  • would want to run ipsi and contra to identify wave V and check for the presence of the peaks
  • –if you are in doubt of wave V, use contra
43
Q

major differences between ipsi and contra recordings

A
  • smaller or absent wave I
  • shorter lantency/smaller amplitude for wave III
  • separation of IV/V waves
44
Q

sweeps as recording parameter for ABR

A
  • no standard
  • 1000 minimum with repetition
  • 1024 or more will have increased SNR
  • the greater the noise the greater number of sweeps needed to clarify the response
  • replications are required to verify result
45
Q

transducer as recording parameter for ABR

A
  • insert earphone, headphone, or bone oscillator
  • –inserts are good because comfortable and prevent both ear canal collapse and cross over
  • –bone vibrator will give wave V as predominant component
46
Q

what are the 5 major signal/stimulus parameters

A

1) stimulus type
2) signal polarity
3) signal rate
4) signal level
5) mode of presentation

47
Q

click stimulus type for ABR

A
  • electric rectangular waves of 0.1 ms duration
  • click ABR and PTA thresholds are highly correlated at high frequencies, mainly 2000 Hz, because this is where most of the click energy is
  • –click generates a response from the base of the cochlea
  • –resonance frequency of transducers peaks between 2-6 kHz
  • disadvantage: low freqs cant be represented in click ABR
  • clicks reflect the synchronous activation (onset type neurons)
48
Q

chirp as ABR stimulus type

A

chirp was developed because the time it takes for a wave to travel through the cochlea, affects the time of the response of each frequencies
*low freqs 1st mean they will reach the apex of the cochlea when the high frequency reaches the base of the cochlea so no phase cancellation of the response because now happening at the same time (so also a bigger response)

49
Q

tone burst as ABR stimulus

A
  • frequency specific signal
  • –0.5KHz is 4-2-4ms
  • —1 kHz is 2-1-2 ms
  • –2k Hz is 1-0.5-1 ms
  • advantage is better correlation with PTA thresholds
  • disadvantage of using TB
  • –less distinct early waves (I,II,and III)
  • –less likely to elicit an identifiable wave V
  • –limited use in otoneurological assessment
  • -more electric artifact during TB generation
  • have to use correction factor to get actual audiometric thresholds
50
Q

stimulus polarity as a signal parameter

A
  • rarefaction is recommended
  • –shorter wave I latency (0.2ms)
  • –greater amplitude
  • –greater differences between infants and adults
  • i think you use condensation if rarefaction isnt god to see if this is better
  • alternating
  • –good for reducing stimulus artifact
51
Q

signal rate as a stimulus parameter

A
  • rate is the number of clicks (or TB) per second
  • recommended rate is 11.1 or 17.1 clicks per second
  • RR us to 30/second gives no amplitude or latency change
  • RR over 40/second is likely to give you 0.4-0.8ms longer wave 5 latency and absent waves I and II
  • RR at 90/second will give you a prolonged latency
52
Q

rule of thumb for selecting ABR rates

A
  • lower rates (under 20/second) when waveform detail is crucial such as in otoneurologic or diagnostic testing
  • higher rates for screening or neurologic exam
  • –for the exam you would want to increase the rate (RR) from 7.7 to 57.7 to see wave V latency shift within 0.8ms
53
Q

signal level as a signal parameter

A
  • at high intensity all waves are observed
  • under 40 dB HL wave II and IV are not seen
  • close to threshold: all waves are reduces and generally wave V is the only wave at threshold
54
Q

what happens with latency with every 10 dB decrease in intensity of stimulus

A
  1. 3ms increase in latency

* note we want a high intensity for neurodiagnosis so we can assess the latency ans see if it is normal

55
Q

latency-intensity functions with ABRs

A
  • system will plot latency (x) intensity (Y) for both air and bone
  • most crucial for interpretation of early EPs
  • compare L-I function with the normal curve
  • –estimate patient threshold sensitivity
  • –can see CHL or SNHL
  • function is nonlinear
  • –at high intensity is a flat slope and latency slightly decreases with intensity over 60 dB HL
  • –with lowering intensity= prolonged latency
  • –near threshold is steep in
56
Q

mode of presentation as stimulus parameter

A
  • monotic vs diotic (binaural) stimulation
  • –binaural stimulation
  • —–produces nearly 2x monaural response
  • —–binaural interaction component (BIC) which is measured by subtracting the diotic response from the sun of monotic response
57
Q

when to use diotic stimulus

A

will give about 2x the effect

  • use when question of no response at all to both monotic stimulation
  • –2x signal=2x SNR
  • in CANS disorders: the CNS is unable to integrate the simultaneous input from both ears so wont see any BIC (2x effect)
58
Q

6 non-pathologic subject variables for ABR

A
  • Age
  • Gender
  • head size
  • body temp
  • race
  • drugs
59
Q

age effect on ABRs

A
  • can be recorded from any age
  • latency decreases and peak amplitude increases for early infancy to young adulthood
  • recorded as early as 27-28 weeks CA
  • wave I is more prominent and prolonged (0.3-1.0 ms) and latency will decrease after birth
  • –later waves are also prolonged in neonates
  • interwave latency intervals (1-5)
  • –shorter with age
  • –longer in neonates (is easily 5.0 ms (4.0 ms in adults)
  • there is prolonged latency and IWI in neonates until neural maturization, earlier in the periphery
60
Q

when are babies adult like with ABRs

A
  • adult like by 18 months
  • need age-dependent norms because of rapid change that occurs within the first 6 months (major changes over the 1st 18 months)
61
Q

Ipsi and contra EPs in children and adults

A
  • similar in older children and adults
  • contra in neonates are smaller and less well definied than ipsi EPs
  • -this is because generators for II IV and V of both sides are only mm apart
62
Q

the aging effect with ABRs

A
  • latency increases between 51 and 74 because of:
  • –reduction of VIII CN
  • –atrophy of spiral ganglion and
  • –degeneration of ganglion cells in the
  • —–VCN, SOC, and MGB
63
Q

gender effect on ABR

A
  • gender difference is probably both intrinsic and in stature (women and smaller generally)
  • women generally have shorter latencies and larger amplitudes than men
  • –smaller head size=shorter latency
64
Q

head size on ABR

A

only has a significant effect in extreme cases

65
Q

body temperature effect on ABR

A
  • hypothermia reduces neural transmission time
  • –leads to an increase in I-V IWL
  • —–correction: 0.2 ms (1-5) for every degree of body temperature below 37 degrees C
  • measured before and during EPs procedure
  • –only monitored in cases where body temp can change
  • —–coma, intraoperative, low birth weight ,etc
66
Q

race effect on ABR

A
  • non-factor probably
  • most normative data was recorded on white subjects
  • no determined effect of other races
  • no determined interaction between race, gender, head size, or temperature
67
Q

ABR and drugs

A
  • large number of sedative anesthetics, tranquilizers, and other drugs have been found to have no significant effect on ABR
  • chloral hydrate, diazepam or one of the barbiturates is typically used for sedation in children when needed
68
Q

test strategies for cochlear vs VIII cranial nerve HL

A
  • audiologic assessment and high level ABR
  • determine absolute and interwave latencies
  • check for symmetry: wave V ILD and I-V IWL
69
Q

test strategies to assess peripheral auditory function

A
  • establish threshold ABR for click
  • tone burst ABR as appropriate
  • verify brainstem function
  • determine absolute and interwave latencies
70
Q

when to use ABR

A
  • difficult to test population
  • when conventional audiometry needs to be validated–suspected nonorganic HL
  • –the ABR response will be within 15-20 dB of behavioral threshold if they are accurate
  • to rule out VIII nerve and brainstem pathology
  • for IOM, trauma, and coma

AUD spring 2020 Electrophys II (13 decks)

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