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Auditory Evoked Responses and Neurodiagnostics > Auditory Brainstem Responses > Flashcards

Auditory Brainstem Responses Flashcards

1
Q

What is a normal ABR characterized by?

A

Five to seven vertex-positive peaks that occur in the time period from 1.4 to 8.0 ms after the onset of a stimulus
Potentially up to seven peaks, but we ignore 6 and 7

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2
Q

What do the waves or peaks of an ABR represent?

A

Sums of neural activity from one or more sources at various discreet points in time

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3
Q

What is the possible neural generator for wave 1?

A

Distal 8th nerve
Presents at about 1.5 ms

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4
Q

What is the possible neural generator for wave 2?

A

Proximal 8th nerve with some contribution from the distal 8th nerve

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5
Q

What is the possible neural generator of wave 3?

A

Neurons in the cochlear nucleus (CN) and possibly fibers entering the CN
About 3.5 ms

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6
Q

What is the possible neural generator of wave 4?

A

Unknown, but 3rd order neurons in the SOC most likely

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7
Q

What is the possible neural generator for wave 5?

A

May be related to the lateral lemniscus and inferior colliculus
About 5.5 ms

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8
Q

What are the other terms for ABRs?

A

BAER
BESR
*All mean the same thing

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9
Q

How long does it take for the response to go from the spiral ganglion to the brainstem?

A

2 ms
If longer, you can localize where the disorder is due to latencies

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10
Q

Where does the majority of the click energy come from?

A

2000 to 4000 Hz
(mostly in the 3-4 kHz range)

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11
Q

Are clicks the preferred stimulus for neurodiagnostics?

A

Yes

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12
Q

Are ABRs a test of hearing?

A

No
It tests the middle chunk of the hearing pathway
Doesn’t tell us everything
*the only way to truly test the whole system (sensory, nervous, and cortical) is with standard audiometry

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13
Q

Can ABRs also be an indication of early damage?

A

Yes

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14
Q

What is the first presentation for ABRs?

A

Click at 80-90 dB nHL
Will be able to get a good response even on those with hearing loss

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15
Q

What are the parameters that we examine in an ABR?

A

Absolute latency
Interwave latency intervals
Interaural latency differences
Latency-intensity functions
Stimulus rate changes
Amplitude
Waveform morphology and replicability

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16
Q

What is absolute latency?

A

The time interval between the stimulus onset and the peak of the waveform
Measured in ms
The most robust and reliable characteristic and provides the mainstay of ABR interpretation
1.5 (I), 3.5 (III), and 5.5 (V) ms (+/- 2 SD built into the system)

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17
Q

Are the standard latencies for higher level stimuli?

A

Yes
75 dB nHL and up
For clicks presented at 75 dB above normal threshold

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18
Q

Are absolute latencies very consistent and repeatable?

A

Yes, for normal individuals
Peak latencies should replicate within 0.1 ms

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19
Q

Is absolute latency also consistent across subjects?

A

Yes
Which makes latency the most robust parameter in the clinical interpretation of the ABR

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20
Q

What are interwave latency intervals?

A

Time period between peaks
Use the latencies of earlier peaks in the response as the reference
Waves I to III
Wave III to V
Waves I to V

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21
Q

What are the norms for interwave latencies?

A

I to III = 2 ms
III to V = 2 ms
I to V = 4

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22
Q

Is wave I most commonly affected by hearing loss?

A

Yes, due to it being such an early response and not a lot generating that response

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23
Q

What area does wave I-III represent?

A

Activity in the 8th nerve and lower brainstem

24
Q

What area does wave III-V represent?

A

Activity primarily in the brainstem

25
What are interaural latency differences?
Compare absolute latencies of wave V obtained from stimulation of the right versus the left ears at equal intensities *Don't need to look at all of the waves for this bc we are assuming that the rest are normal if wave V looks as expected
26
What are the norms for interaural latency differences?
When peripheral hearing sensitivity is similar in each ear, the latency of wav V should differ by no more than 0.2 to 0.4 ms between ears
27
What are latency intensity functions?
As the stimulus intensity decreases, latencies increase and amplitudes decrease As the stimulus intensity increases, latencies decrease and amplitudes increase Measuring the responses at wave V at multiple different intensities
28
What are the latency-intensity function norms?
Latency increases occur slowly for intensities from 90 to 60 dB nHL Latency increases more rapidly at lower intensities
29
Do latency-intensity functions differ depending on the nature of the hearing disorder?
Yes Present differently for conductive, cochlear, and retrocochlear lesions
30
What is the latency-intensity function for conductive hearing losses?
Prolonged absolute latencies for all waves Due to the actual intensity of the stimulus reaching the cochlea is decreased by the presence of the conductive problem
31
What is the latency-intensity function for those with cochlear hearing losses?
Normal latencies at higher intensities and prolonged latencies at lower intensities Steeper than normal LIF
32
What is the latency-intensity function for retrocochlear disorders?
Often will show the same wave V latency prolongation as conductive hearing losses Due to this similarity, it is important to determine the presence of a conductive loss/component in the loss with audiometry or bone-conduction ABR
33
Besides bone-conduction, how can conductive losses be distinguished from retrocochlear losses?
Comparing the latencies of earlier peaks of the ABR In CHL, all waves will be offset by equal amounts In retrocochlear, earlier peaks may be within normal limits
34
Does increasing the stimulus rate change the latency and amplitude of the ABR?
Yes Generally doesn't have a huge effect in a normal system (usually just a slightest elongation) - more robust responses occur when it has time to regenerate High stimulus rates can be employed to evaluate neural synchrony and recovery Use of higher rates may sensitize testing to subtle neural disorders
35
How much does the stimulus rate cause latency increases?
Increasing the rate from 10/sec to 100/sec, will result in a wave V latency increase by approx 0.5 ms (in normal individuals) Need to go to rates much higher than that to see a more pronounced latency
36
Is the latency of earlier components of the ABR generally less affected by the stimulus rate?
Yes Resulting in an increase in the interwave latency as a function of rate
37
Does the amplitude change with stimulus rate?
No, amplitude of wave V remains fairly consistent Whereas the amplitude of earlier waves decreases This results in changes in amplitude ratios and emphasizes the importance of considering the rate of presentation when comparing amplitude ratios to normal data
38
How many stimulus rates do you perform?
2 slow rates 2 medium rates 2 fast rates
39
What is the normal amplitude range of ABRs?
0.1 to 1 microvolt As the stimulus intensity decreases, the response amplitude decreases Not a super important consideration for ABRs Measured as peak-to-peak amplitude (peak to trough)
40
Do lower amplitude earlier peaks become obscured in the background noise first?
Yes With wave V remaining visible at the lowest intensities
41
Which peak of the wave V complex (IV or V) is used when calculating amplitude?
The higher of the two peaks This amplitude is the largest of all peaks in ABRs obtained from individuals over 18 months of age and should exceed the amplitude of wave I
42
Is it useful to compare the amplitude of wave V and wave I as a ratio?
It can be May provide diagnostically significant information Ratios of less than 1.0 seldom occur in normal or cochlear losses, but may be present in retrocochlear losses Amplitude is more variable than latency, so clinical application tends to be limited
43
Should ABR recordings at higher intensities (75 dB nHL) have well-defined peaks?
Yes, and waves I, III, and V should be present for each ear In individuals with significant peripheral HL, the earlier peaks may be reduced in amplitude
44
What kind of ABRs are used for neurological testing for differential diagnosis?
Rate study or neurologic ABR Can be used to assist in determination of the presence or absence of a disorder, and to a limited extent the site of the disorder Can also be helpful in identification of diffuse lesions, such as those associated with MS and disorders that are not associated with a radiologically identifiable lesion
45
What reports indicate an ABR for differential diagnosis?
Unexplained unilateral or asymmetric SNHL Abnormally poor word recognition in quiet Reduced word recognition in noise PIPB rollover Sudden hearing loss Progressive hearing loss Tinnitus or dizziness with no hearing loss Unexplained elevation or absence of MEMR
46
What are the test protocols for differential diagnostic ABRs?
Click stimuli presented at a level well above threshold (70 to 90 dB nHL) to each ear individually No universal standard Initial rates of stimulus presentation ranging from ≈ 10 to 30 stimuli per second used to obtain baseline information (presentation rates such as 11.1 or 27.7 stimuli per second are used to avoid repetition rates that are multiples of 60 Hz that could introduce artifact into the response and/or standing waves) Do low rates, mid rates, and high rates
47
What should you do if clear responses are not obtained at rates of 11.7 or 27.7?
The presentation should be decreased below 10 per second (7.7/sec)
48
What should be done if clear responses are not obtained at the initial test stimuli intensity?
Then the intensity may be increased to further define responses
49
What are some methods to increase the wave I response?
Increasing the intensity of the stimulus Decreasing the presentation rate Comparing rarefaction and condensation clicks to distinguish cochlear potentials from neural responses Gen closer to generator site (TM electrode) Use a horizontal recording montage (A1-A2)
50
Should the degree of hearing loss preclude an attempt to obtain an ABR?
No, you should always try Although, this can make them more difficult to obtain and can affect the latency and amplitude Can still get wave V for loses up to 60 to 70 dB HL Wave V latency and waveform morphology are progressively affected by greater degree of peripheral hearing loss and by increasing slopes of loss
51
What level of hearing loss results in wave I disappearing?
Loss at 4 kHz exceeding 50 dB When thresholds from 2k – 4k Hz are in the 50-70 dB HL range the overall number of abnormal ABRs increased
52
Did patients with sharply sloping downward sloping audiograms show wave V delays?
Yes Which is probably related to stimulation of fewer basal and more apical regions of the cochlea Patients with rising audiograms, especially those with best hearing at 2,k, 3k, and 4k Hz, are more likely to yield normal ABRs
53
Should some components of the response be observed at levels within 10 to 20 dB of threshold?
Yes
54
Are ABRs sensitive to neurological disorders of the 8th nerve and low to mid brainstem?
Yes These disorders include space-occupying lesions, diffuse lesions, and functional (physiological) abnormalities
55
Are ABRs sensitive to all central nervous system disorders?
No The ABR does not evaluate the integrity of the CNS rostral to (above) the brainstem, so cortical deafness can not be ruled out on the basis of a normal ABR
56
What affect can 8th nerve tumors and other neoplasms have on ABRs?
Prolongation of absolute latency Prolongation of interpeak latencies Degradation of waveform morphology Absence of wave (particularly the later ones)

Auditory Evoked Responses and Neurodiagnostics (6 decks)

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