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Year 2 Courses > Evoked Responses Midterm > Flashcards

Evoked Responses Midterm Flashcards

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1
Q

The ABR is not sensitive…

A

to all central nervous system disorders, it is only sensitive from ear to brainstem

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2
Q

what is an auditory brainstem response (ABR/BAER)?

A

complex response to certain types of external stimuli that represents neural activity that is generated at several anatomical sites

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3
Q

how is a normal ABR characterized - NUMBERS

A

5 to 7 positive peaks that occur in the time period from 1.4 to 8.0 ms after the onset of a stimulus

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4
Q

with an ABR, what are we looking at

A

neural activity that is generated along the auditory pathway and is a test of neural synchrony

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5
Q

what do waves of an ABR represent?

A

sums of neural activity along the auditory pathway and is a test of neural synchrony

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6
Q

what are the neural generators of the ABR for waves 1-5?

A

wave 1: distal 8th nerve, spiral ganglion
wave 2: proximal 8th nerve
wave 3: cochlear nucleus and fibers entering the CN
wave 4: unknown but most likely the SOC
wave 5: lateral lemniscus and inferior colliculus

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7
Q

which ABR waves are we interested in?

A

1,3, & 5

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8
Q

as the intensity decreases, we are typically only going to see wave _____

A

5

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9
Q

what ABR parameters are typically inspected?

A

absolute latency, inter wave latency intervals (IWI), interaural latency differences, latency intensity functions (LIF), stimulus rate changes, amplitude, waveform morphology and replicability

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10
Q

what is absolute latency?

A

time between stimulus onset and peak of the wave ; measured in milliseconds
-this is the hallmark for analysis of ABRs and is the most reliable characteristic of ABRs
-very consistent and repeatable

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11
Q

what are the norms for absolute latency?

A

wave 1: around 1.5 ms
wave 3: around 3.5 ms
wave 5: around 5.5 ms

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12
Q

what are interwave latency intervals (IWI)?

A

the time b/w each peak

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13
Q

what are the norms for interwave latency intervals (IWI)?

A

wave 1-3: around 2 ms
waves 3-5: around 2 ms
waves 1-5: around 4 ms

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14
Q

what does the interwave latency interval for wave 1-3 represent?

A

represents synchronous activity in the 8th nerve and lower brainstem

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14
Q

what does the interwave latency interval for wave 3-5 represent?

A

reflecting activity within the brainstem

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15
Q

what does the interwave latency interval for wave 1-5 represent?

A

a representation of overall activity from the 8th nerve and the nuclei of the brainstem responsive to auditory stimuli

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16
Q

what do interaural latency differences look at?

A

they compare absolute latencies of wave 5 obtained from the right and left war to see if they are equal or if there is any sort of asymmetry

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17
Q

what are the interaural latency differences norms?

A

each ear’s wave 5 should be within 0.2-0.4 ms

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18
Q

what are latency intensity functions (LIF)?

A

looking at the relationship between latency and intensity by plotting the absolute latencies of wave 5 as a function of intensity

a way to measure and show how quickly your brain (or auditory system) responds to sounds of different loudness levels.

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19
Q

what will typically occur with latency as the intensity gets adjusted and why?

A

as we decrease the intensity the latency will increase
-with softer signals they will activate less neurons resulting in needing a longer time period to ensure we get enough neurons to make the signal

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20
Q

if the patient has normal hearing what will the latency intensity functions look like?

A

seeing a decrease in latencies as the intensity increases

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21
Q

if the patient has conductive hearing loss, what will the latency intensity functions look like?

A

there is a prolonged shift of absolute latencies at all waves
-all peaks are prolonged, so the interpeak latencies will remain the same
-LIF will be plotted above the norms

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22
Q

if the patient has cochlear hearing loss, what will the latency intensity functions look like?

A

there is a steeper growth in latencies with a decrease in amplitude
-there will be prolonged latencies at lower intensities and normal latencies at higher intensities

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23
Q

if the patient has retrocochlear hearing loss, what will the latency intensity functions look like?

A

will show prolonged latencies of every wave, similar to conductive

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24
how can we differentiate between conductive and retrocochlear HL?
based off of the LIF we cannot tell the difference so we will need to look at the BC ABR in order to determine if there are ABGs or not
25
what are stimulus rate changes?
observing the relationship of rate, latency and amplitude -latency of earlier components will generally be less impacted by stimulus changes when compared to later components resulting in an increase in the IWI as a function of rate -amplitude of wave 5 is more consistent as rate increases whereas amplitude of earlier waves decreases
26
what is amplitude?
looking at peak to peak amplitude, so the positive peak to the following negative trough
27
what are the norms for amplitude? what is the goal when looking at amplitude?
0.1 to 1 microvolts -we see this decrease as the intensity decreases -trying to identify the lowest level that we can detect wave 5 at
28
tell me about waveform morphology and replicability?
the subjective component of the recording and observing how the waveform looks -everything should be replicable
29
how can the ABR be used for differential diagnosis?
they can be helpful in identification of diffuse lesions, such as those like MS, and disorders that are not associated with any radiologically identifiable lesions, such as auditory neuropathy
30
what is a neurologic (rate study) ABR?
used to assess neural function with an emphasis on identifying types of abnormalities such as MS -used to assist in determination of the presence or absence of a disorder -used to with limited extent, identify site of disorder
31
What types of patients would we do rate study ABR's on?
patients who report or present with : -unexplained unilateral or asymmetrical SNHL -abnormally poor WRS in quiet -reduced WRS in noise PIPB rollover -sudden HL
32
why would we perform a rate study?
-unexplained asymmetry -elevated or absent ME reflex -poor WRS in quiet -unexplained dizziness -unilateral tinnitus -PIPB rollover -sudden HL of unknown cause -poor inter test reliability -to aid in diagnosis of demyelinating conditions
33
what are the main parameters that we look at within neurologic (rate) studies?
latencies -both absolute and interpeak
34
what stimulus is used with neurologic (rate) studies?
-click -low and fast rate -high intensity (80 dB nHL) -single polarity -repetition +/- 1500 sweeps -masking at 55 dB nHL (if needed)
35
what is our typical ABR protocol?
-click presented at a well above threshold level to each ear individually (70-90 dB nHL) -individual rates of stimulus presented ranging from 10 to 30 stimuli per second, used to obtain baseline information -when responses are not obtained at rates of 11.7 or 27.7, the presentation rate should be decreased below 10 per second
36
why do we make sure to first present an ABR at a level well above threshold?
to ensure that we can get a good response from the patient
37
how can we make a cleaner response in terms of the stimulus parameters?
slow the rate down and increase the intensity
38
with an identifiable wave 1, how is it impacted as we continue to record? wave 1 is hard to see in what individuals?
it becomes difficult to identify when testing people with a HF HL
39
what are some methods to increase the amplitude of wave 1?
-increase intensity -decrease rate -comparing rarefaction and condensation clicks -use a TM electrode with ECochG -use a transtympanic ECochG -use a horizontal recording montage (A1-A2)
40
how can the ABR be impacted by neurological disorders?
-prolonged absolute latencies -prolonged interwave latencies -degraded waveform morphology -absence of waves (particularly later ones)
41
ABRs are sensitive to neurological disorders on the 8th nerve and low-mid brainstems which can include space occupying lesions, diffuse lesions and functional abnormalities however …..
not all CNS disorders will be identified as only those from the ear to the brainstem will be identified
42
what is the usefulness of the ABR?
-can evaluate the auditory pathway from the cochlea to brainstem -can help give information regarding hearing status -a non invasive, painless procedure
43
what are the limitations of the ABR?
-not sensitive to all central nervous system disorders -does not evaluate the integrity of the CNS rostral to the brainstem, so cortical deafness cannot be ruled out based on a normal ABR
44
what do we mean by that ABR is not a test of hearing?
the ABR is not a test of hearing as we are only looking at a portion of the auditory pathway -we are not getting any information regarding the periphery or central aspects -yes we can get thresholds from an ABR, but we need to be careful with the language that we document it with
45
what is a tone burst ABR?
generated by a tone burst stimulus giving a different appearance from that of an ABR generated by a click -with tone bursts, earlier waves are not often noticed but wave 5 will be easily identified
46
what is the stimulus polarity with tone burst ABR?
typically will run once with alternating in order to rule out ANSD then will select condensation or rarefaction for the remainder of the runs
47
how does normative data work with tone burst ABRs?
each tone burst ABR data is compared to sets of data that has been collected from normal hearing individuals -this is done within a clinic, by the equipment that is used or can be based on individually collected data
48
with tone burst ABRs, one consideration is determining if we want to allow for 2 SD or 3 SD from the norm. how does either effect referral criteria
+/- 2 SD: placing more normal patients outside of the normal range, impacting the specificity +/- 3 SD: including more abnormal subjects into the normal range, impacting the sensitivity
49
ABRs generally mature to adult-like features around?
2 years old
50
how do ABRs compare between infants and adults
-at birth waveforms are incomplete and will generally only view waves 1, 3 and 5 -for infants wave 1 is often bigger whereas for adults wave 5 is bigger -for infants their INTERWAVE LATENCY INTERVALS are prolonged with 1-5 coming in around 5 ms whereas for adults 1-5 comes in around 4 ms
51
during the first 18 months of life, what change occurs within the ABR?
wave 3 and 5 become shortened in latency
52
when selecting the LIF we want to use for out patient's ABR, what is the most important thing to do
select the correct age and stimulus !
53
what is a threshold (hearing sensitivity) ABR?
used to estimate sensitivity and to evaluate for ANSD
54
what is the stimulus used for threshold ABR?
-toneburst or chirp -rate of 33.3 or 37.1-49.1 -polarity being rarefaction/alternating at higher intensity -ramping of 2-0-2 -between 700 and 1500 sweeps -masking at 55 dB nHL if needed
55
what is the 3 part protocol for threshold ABR?
1. ABR clicks 2. ABR tone burst 3. ABR bone conduction clicks
56
tell me about part 1 of the protocol - ABR clicks for threshold ABR
-click stimulus with both rarefaction and condensation -obtain two responses for each ear at 75 dB nHL click -after the high level with both polarities, select one to continue with -decrease click in 20 dB steps until no response is obtained, with repeating twice to ensure repeatable wave
57
tell me about part 2 of the protocol - ABR tone burst for threshold ABR
-run at 500 Hz then again at 4000 Hz -decrease intensity in 10 dB steps until no response is obtained -use only one polarity
58
tell me about part 3 of the protocol - ABR bone conduction for threshold ABR
only will be conducted if tone bursts are not at expected normal levels -present at decreasing levels through BC to identify if there is a difference in levels at which the responses are obtained
59
what are the correction factors for threshold ABR?
each frequency will have its own correction factor that takes it from dB nHL to dB HL, ensuring that the value we found can be compatible to a threshold that can be found within a booth
60
how do we mask for ABR?
this is not typically needed however if wave 1 is not where it should be then we would want to mask to be sure this is not occurring from cross over -masking will be set to a fixed level
61
what is a bone conduction ABR?
helps to determine if the HL is conductive, sensory or mixed -providing ear specific information without limitations of masking the NTS -BC responses will be earlier than AC as it does not have to travel as far as AC does and therefore the latencies are typically shorter
62
typically, how much shorter are BC latencies when compared to AC?
around 0.5 ms earlier
63
what is a stacked ABR? what is it used for?
a more sensitive test for identifying any space occupying lesions by taking an ABR and separating the components into frequencies and comparing the wave 5 amplitudes
64
why are stacked ABR no longer used today?
they are not feasible due to time constraints of needing to record, shift, sum them then compare to normative data -then once the chrip was created it has the same principles so stacked became obsolete
65
what is a chirp stimulus?
different components will be released but they are all off set so that they arrive at the same time -this creates one signal that travels through at the same time resulting in a cleaner and bigger wave 5
66
what is the hallmark of an ABR recording, meaning what is the most important/reliable component that we look at?
absolute latency
67
what occurs with amplitude as the intensity decreases? increases?
decreases ; increases
68
what occurs with latency as the intensity decreases? increases?
increases (widens) ; decreases (narrows in)

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