2. Abr

Front 1

ABR

Back 1

a far-field recording of neurologic activity of the VIII nerve and brainstem auditory pathways that occurs over the first 10 to 15 sec after a suitable sound stimulus has been delivered to the ear

Front 2

Who discovered the ABR? When?

Back 2

Don Jewett in the late 1960s

Front 3

What about the first publication?

Back 3

in 1971 written by Jewett and Wilson

Front 4

ABR components

Back 4

stimulus

major peaks in the waveform

response latency

Front 5

ABR atimulus

Back 5

high-intensity transient acoustic signal

Front 6

waveforms

Back 6

by Roman numerals

Waves I through Waves V

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response latency

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within a 5 to 6 ms period following the presentation of a high intensity stimulus

Front 8

Generators of waves

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Wave I: distal VIII nerve

Wave II: proximal (brainstem portion) of the VIII nerve

Later waves: have multiple generators within the auditory brainstem

Front 9

What do peaks represent in ABR?

Back 9

synchronous neural discharge from dipole generators located at various way stations along the auditory pathway

Front 10

Where do waves I, II, and III arise?

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from auditory pathways IPSILATERAL to the side of stimulation

Front 11

Where does wave V arise?

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it reflects activity in midbrain auditory structures CONTRALATERAL to the stimulus

Front 12

What do latencies for later conponents depend on?

Back 12

synaptic activity in major brainstem auditory centers

Front 13

In pots with normal hearing, what is click evoked ABR mostly dependent on?

Back 13

activation of the higher frequency (3 kHz) region of the cochlea

Front 14

optimal ABR stimulus

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brief duration (e.g., 0.1 ms) click because it enhances synchronous neural activity

Front 15

tone burst stimuli are also effective in eliciting the ABR

Back 15

yes yes yes yes yes

Front 16

ABR stimulus rate

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20/second or even faster is effective in evoking the ABR

Front 17

As rate increase...

Back 17

ABR latency increases

ABR amplitude decreases

Front 18

Rate influences ABR latency more fore...

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• premature than term neonates
• young children (under 18 mo) than older children
• Older children (up to 13 yrs) than adults

Front 19

As stimulus intensity increases...

Back 19

response latency values decrease

response amplitude increases

Front 20

When intensity is above 70 dB nHL

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latency remains stable

amplitude continues to increase

Front 21

ABR stimulus polarity

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rarefaction

condensation

alternating

Front 22

rarefaction

Back 22

• pressure wave in a negative direction
• produced by movement of the transmitter diaphragm AWAY FROM the TM
• activation of VII nerve caused by upward movement of BM secondary to rarefaction polarity stimulus
• activates of DEPOLARIZES cochlear hair cells
• creates shorter latencies and greater amplitude

Front 23

condensation

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• positive electrical pulses
• produced by movement of the transmitter diaphragm TOWARD the TM
• may produce HYPERPOLARIZATION of hair cells

Front 24

alternating

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• switching between condensation and rarefaction polarities at subsequent stimulus presentations
• can produce out-of-phase responses (reduced amplitude and abnormal responses)

Front 25

What are repetitions/sweeps used to?

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to extract and enhance AERs from background neurologic activity

Front 26

How many sweeps to use?

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enough to produce an adequate SNR for confident ABR wave analysis (no more or no less)

Front 27

minimally recorded ABR electrode placement

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• one electrode located either at the top of the head (vertex) or high in the midline on the forehead
• another electrode located near the ear (earlobe) on the stimulated side
• a ground (common) electrode can be located anywhere (low forehead most common)

Front 28

ABR acquisition is detected within post-stimulus analysis time of....

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15 ms

shorter or longer analysis times may be appropriate under certain test conditions

Front 29

band-pass filter settings

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• 30 or 100
• 1500 or 3000 Hz

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high pass filter

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• as cutoff is increased from a low frequency (0.1 Hz) to higher frequency (500 Hz)
• wave components (wave V) are reduced in amplitude and distortions in latency often are noted (poor morphology of waveforms)

Front 31

low pass filter

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• decreasing cutoff frequency from a very high value (10,000 Hz) to 3000 Hz eliminated noise without distorting ABR latency and amplitude
• ABR contains almost no spectral energy above 2 kHz

Front 32

parameters for evaluating ABR

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absolute latency

interwave latency intervals

amplitude

Front 33

know this for sure

Back 33

Front 34

ABR absolute latency is time between...

Back 34

stimulus onset and the peak ABR waveforms

Front 35

ABR absolute latency norms are recorded with a stimulus that is

Back 35

a click stimulus of 75 dB above normal threshold

Front 36

when should absolute latencies occur?

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Wave I: 1.6 ms

Wave III: 3.7 ms

Wave V: 5.6 ms

Front 37

absolute latency is great in ____ and shorter in ___

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newborns

females

Front 38

latencies of ABR waves increase as the stimulus ___

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decreases

Front 39

ABR latency-intensity function

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Front 40

ABR interwave latency

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the time between peaks in the waveform

Front 41

interwave latency times

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Waves I-III and III-V: 2.0 ms

Waves I-V: 4.0 ms

Front 42

What information is provided from interweave latency

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about the auditory pathways

useful in the neuroldiagnostic ABR approach

Front 43

I-III interwave latency reflects...

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VIII nerve and lower brainstem auditory pathways

Front 44

III-V interwave latency reflects...

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brainstem activity

Front 45

I-V interwave latency reflects...

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a representation of overall activity from VIII nerve and the nuclei and tracts of the brainstem responsive to auditory stimuli

Front 46

range of normal ABR amplitudes

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between .1 to 1.0 microvolts

Front 47

amplitudes will decrease as the stimulus intensity ____

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decreases

Front 48

the "area under the curve" represents

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the total amount of neural energy contributing to the evoked response

Front 49

What has been proposed as the "area under the curve"

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alternative method of quantifying the response of an AMLR

Front 50

How is under the curve measured

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by examining amplitudes as a function of time

by marking the negative peak of one wave to the next negative peak in the waveform

can only be measured using both positive or both negative peaks

Front 51

FFT can be performed on ABR waveforms

Back 51

yep

Front 52

what does ABR spectral analysis allow?

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the major frequencies within the AEP to be separated and analyzed after the waveform has been recorded

Front 53

according to Hall, most energy in an ABR is (low/high) frequency

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low

very little energy is contained above 2 kHz in an ABR waveform

Front 54

other frequencies with prominent energy regions include

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500 to 600 Hz

900 to 1100 Hz

Front 55

Why is it important to consider FFT in spectral analysis

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consider it when setting the high and low pass filters for an ABR recording in order to preserve as much as the ABR waveform as possible

Front 56

What is the purpose of the FFT?

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to demonstrate that most energy in an ABR is low in frequency, below 1500 Hz

Front 57

Specifically, where is most energy found?

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below 500 Hz (most concentrated around 30-40 Hz)

Front 58

ABR spectral analysis

Back 58

Front 59

ABR Fsp values are used to determine what

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the quality of the evoked response in relationship to the noise in the recording

Front 60

What is the premise of Fsp values

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the evoked potential to the auditory stimulus is rather constant (in amplitude, latency, and morphology) from presentation while is noise in recording is more random

Front 61

ABR Fsp values represent...

Back 61

a single point in the recording

gives the probability of the response actually being an ABR response

not ambient background activity

Front 62

higher the Fsp

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the better the ABR response can be considered

Front 63

what Fsp values can be considered a response

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value of 1 to 3

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when is Fsp calculated?

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for every 250 sweeps

Front 65

ABR Fsp values can be used to limit...

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the number sweeps needed to record an accurate ABR response at higher intensities

Front 66

what can ABR Fsp be used to determine

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when more averaging will not produce a response

Front 67

ABR Fsp can reduce test time when using what?

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the minimum number of sweeps when recording AEPs

Front 68

ABR Fsp can be used to increase...

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objectivity and limit the interpretive errors in clinical AER measurement

Front 69

the response is not seriously affected by..

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subject state of arousal (sleep)

most drugs, including sedatives and anesthetic agents

Front 70

age influences on ABR

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latency increases

• under 18 months
• over the age of 60 years

Front 71

ABR and infants waveform

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Front 72

gender influences on ABR

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females have

• shorter latency values
• larger amplitudes

Front 73

clinical importance of gender influences

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balance males and females when establishing normative data

Front 74

body temperature influencing ABR

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consider for patients with

• infection (high temp) - latency decreased
• coma, alcohol, anesthesia (low temp) - latency decreased
• severe hypothermia - ABR disappears

Front 75

ABR normal variations

Back 75

Front 76

for the neurodiagnostic application of ABR, the peripheral system is assumed to...

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function properly and the retrocochlear system is examined

Front 77

clinical applications of neurodiagnostic ABR

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• neurodiagnosis of VIII nerve or auditory brainstem dysfunction
• monitoring VIII nerve and auditory brainstem status intraoperatively during surgery potentially auditory system
• diagnosis of auditory neuropathy

Front 78

neurodiagnostic ABR

click rate?

analysis time?

stimulus level?

Back 78

slower click rate - 10 to 20 per sec

10 to 12 ms analysis time

70 to 100 dB HL stimulus levels

Front 79

response parameters for neurodiagnostic ABR

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• electrode array (Cz/A1 and Cz/A2)
• time window (15 ms)
• delay (-3 ms)
• low freq filter (30 Hz)
• high freq filter (3 kHz)
• sensitivity (50 uV)
• repetitions (2k at max)

Front 80

stimulus parameters for neurodiagnostic ABR

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• type (click)
• duration (100 usec)
• intensity (80 dB nHL)
• polarity (rarefaction)
• rate (11.4/sec)

Front 81

When estimating hearing thresholds or auditory sensitivity, it is assumed

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that the auditory pathways are intact

Front 82

clinical applications for threshold ABR

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• newborn infant auditory screening
• estimation of auditory sensitivity in infants and DTT children, including frequency specific information at audiometric frequencies

Front 83

with advent of UNHS, ABR has assumed an essential role as...

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an électrophysiologie technique for estimating auditory threshold in infants at risk for hearing loss

Front 84

faster click rate for threshold ABR

longer analysis window for threshold ABR

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30 to 70 per sec

20 to 25 ms

Front 85

response parameters for threshold ABR

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• electrode array (Cz/A1 and Cz/A2)
• time window (18 ms)
• delay (-3 ms)
• low freq filter (30 Hz)
• high freq filter (3 kHz)
• sensitivity (50 uV)
• repetitions (2k at max)

Front 86

stimulus parameters for threshold ABR

Back 86

• type (click or tone burst)
• duration (100 usec)
• intensity (80 dB nHL - then decreases in intensity)
• polarity (rarefaction)
• rate (31.4/sec at max)

Front 87

clinical limitations for ABR

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with click stimuli, the ABR only estimates hearing sensitivity int he 1000 to 4000 Hz region and now for lower frequencies (can also be evoked with frequency specific signals)

the ABR is not a test of hearing (evoked with simple acoustic signals and is generated mostly by onset neurons)

ABR provides no information on auditory function above the level of the brainstem (auditory cortex)