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Diagnostic Audiology > Auditory brainstem response (ABR) > Flashcards

Auditory brainstem response (ABR) Flashcards

1
Q

What the definition of electrophysiology?

A

Measurement of electrical activity which is a biproduct of physiological activity

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2
Q

What is the definition of evoked potentials?

A

Measurement of electrophysiological activity associated with sensory stimuli

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3
Q

What are the applications of measurement of auditory evoked potentials?

A

-Can help determine the site of lesion
-Threshold estimation
-Measure of auditory processing
-Intraoperative monitoring
-Neonatal hearing screening
-Objective measures

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4
Q

What are the principles of evoked potentials?

A

-It is possible to measure electrical activity associated with peripheral or central neural activity
-Variations in electrical activity are associated with a change in voltage
-Response is linked to the stimulus- therefore we need to know the stimulus we are going to use and its parameters

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5
Q

What is the neurophysiological basis of evoked potentials?

A

-Neuro-electric field is generated by nerve action potentials
-Synchronisation of a large number of neural responses
-Change in electrical potential over time
-The smaller or more diffuse the potential, the nearer the measurement system must be as it is harder for us to pick it up

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6
Q

What is the difference between far- field and near field recordings?

A

-Far field measurements involve measuring from scalp electrodes which creates barriers between the response and where we are recording it
-Near field measurements are recorded close to the generator site

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7
Q

What are the parameters of evoked potentials that we are interested in?

A

-Magnitude (amplitude)
-Latency
-Presence/ absence

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8
Q

How are auditory potentials classified according to their latency?

A

-The auditory brainstem response (ABR) is an early potential
-The MLR (middle latency response) is in the middle
-SLR (slow latency response) has slow latency
-This is measured in ms a time from the stimulus presentation as the time of occurrence of a specific stimulus

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9
Q

What is the magnitude of the response a measurement of?

A

-The magnitude= amplitude= voltage
-Peaks in amplitude are associated with synchronous neural activity and have a typical range

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10
Q

What time frame is associated with a short latency?

A

0 to 10 ms

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11
Q

What time frame is associated with a middle latency?

A

10 to 100 ms

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12
Q

What time frame is associated with a slow latency?

A

100 to 300 ms

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13
Q

What time frame is associated with a late latency?

A

300+ ms

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14
Q

What is the post-auricular muscle (PAM) response?

A

-The muscle response
-This response is an artefact as it happens far too early to be an evoked potential response
-Can be diminished by getting the patient to relax more or open their jaw

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15
Q

What is the auditory brainstem response (ABR)?

A

-Event-related potential (the event is sound)
-It is a very small response (1 uv)
-May be picked up from scalp electrodes
-Transient response (evoked)
-Occurs 1-15 ms after the stimulus (early)

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16
Q

What are the major measures of the ABR?

A

Amplitude and latencies

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17
Q

What are the four main brain nuclei which are responsible for the generation of the ABR?

A
  1. Cochlear nucleus (first synapse point, tonotopically organised)
  2. Superior olive (located in lower pons, involved in understanding speech in noise, localisation and first place of bilateral representation)
  3. Inferior colliculus (midbrain, tonotopical organisation, involved with localisation and communicates with superior colliculus)
  4. Medial geniculate body (thalamus, receives sensory input and projects to the primary auditory cortex)
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18
Q

What is the lateral lemniscus?

A

The largest tract of auditory fibres that carry information of the cochlear nucleus and superior olivary complex to the inferior colliculus in the midbrain

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19
Q

What are the cortical and subcortical areas associated with the auditory brainstem response?

A

-Heschl’s gyrus
-Planum temporal
-Sylvian Fissure

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20
Q

Where does each ABR wave originate from?

A

-Wave I and wave II come from specific parts of the auditory pathway but other than that each ABR component has multiple generators and results as the combination of electrical activity of several brainstem nuclei
-One anatomic structure may give rise to more than one ABR wave and more than one anatomic structure may contribute to a single ABR wave

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21
Q

Why are objective indicators important for determining the presence of an ABR?

A

-Experience is required to judge that a response is present (e.g. a wave V)
-Clinicians often disagree on the threshold value
-This makes a supposedly objective test actually subjective

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22
Q

State the factors that will influence ABR results

A
  1. Non-pathological subject factors
  2. Stimulus factors
  3. Acquisition factors
  4. Pathological subject factors
    -Tester interpretation
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23
Q

What are the non-pathological subject factors which will influence the ABR?

A
  1. Age- lack of myelin around the nerve reduces transmission of the signal
  2. Gender
  3. Body temperature
  4. State of arousal
  5. Drugs
  6. Muscle activity
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24
Q

What are the stimulus factors that will influence the ABR?

A
  1. Frequency
  2. Duration
  3. Intensity- louder sounds trigger a response in more nerves
  4. Rate
  5. Polarity
  6. Transducer
  7. Masking
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25
Q

What are the acquisition factors (how are you playing and recording the sound) that will influence the ABR?

A
  1. Filtering- if it is below 50 Hz you might be more likely to get main interferences
  2. Electrodes and their position
  3. Amplification
  4. Time window- how long are you screening for
  5. Signal averaging- how clear is your response
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26
Q

What are the pathological subject factors which will affect the ABR?

A
  1. Degree and pattern of hearing loss
  2. Neural/ CNS site of lesion
  3. Neuropathology e.g. neurological condition which is systemic
  4. Decreased consciousness (only affects later AEPs)
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27
Q

What is the pathway that sound takes once it enters the inner ear?

A

-The cochlea changes the sound into action potentials which are coded for frequency, intensity and timing
-Cochlear division of the VIIIth nerve in the cochlear nucleus carries this information to the brain
-The information undergoes processing in the brainstem and thalamus before reaching the cortex

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28
Q

How is the ABR measured?

A

-Surface/ scalp electrodes are placed on the forehead and the ear lobe/ mastoid bone of the patient (far-field recordings)
-Recorded as 5 main waves of electrical activity from the VIII nerve to the brainstem

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29
Q

Describe the 5 different ABR waveforms

A

Wave I is very robust, wave II not so much, wave III is sometimes even bigger than V but IV and V are expected to be a complex, wave V is the one just before the big drop off

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30
Q

What are the two clinical applications of the ABR?

A
  1. Audiological- finding thresholds, screeing for hearing loss
  2. Oto-neurological- looking at the morphology, what it looks like and how that relates to function
31
Q

What is neurological ABR used for? What stimulus does it require?

A

-Identification of neurological abnormality in the VIII nerve and brainstem pathway
-Uses AC click (broadband stimulus)

32
Q

What is a common clinical application of the audiological ABR? What stimulus does it use?

A

-Testing newborn babies and children and adults who cannot be tested behaviourally
-Estimates hearing sensitivity based on the presence of a response at various intensity levels
-Uses frequency specific clicks, tone bursts or chirps

33
Q

Is ABR affected by a patient’s state of arousal?

A

No, and the patient can even be under sedation or anaesthesia

34
Q

Which ABR peaks are the most easily identifiable and reliable?

A

Peaks I, III and V

35
Q

What does the latency and amplitude of the ABR refer to?

A

-Latency: time from stimulus onset to emergence of peak or trough
-Amplitude: size of the peak to peak measure or baseline to peak for I, III and V

36
Q

State the factors affecting the ABR

A
  1. Age
  2. Gender
  3. Stimulus (intensity, time, polarity, duration, repetition rate, masking)
  4. Filters (bandwidth)
  5. Recording site (electrode position)
37
Q

How does age affect the ABR?

A

-Infants below the age of 2 have prolonged latencies due to incomplete myelination
-Need to factor in premature babies who are more susceptible to hearing loss
-Increase in V latency of 0.2 ms between 25 and 55
-Progressive increase in latencies above the age of 65 due to degenerative process

38
Q

How does gender affect the ABR?

A

-Females have shorter latencies and higher amplitudes
-Difference of 0.1 to 0.2 ms
-There is a positive relationship between a smaller and the ABR peak latency
-The travelling wave is faster in the cochlea of women

39
Q

How does the stimulus intensity affect the ABR?

A

-Increase in stimulus intensity results in higher amplitudes and shorter latencies
-Decreasing intensity results in increasing latencies and decreases in amplitude

40
Q

What is the optimal placement of electrodes for the ABR?

A

-Only want minimal amount of electrodes e.g. 3
-The positive (non-inverting) electrode should be placed as high up into the hairline as you can get
-The negative (inverting) electrode should be placed on the ipsilateral mastoid
-The common electrode should be placed on the contralateral mastoid

41
Q

What does polarity refer to when we are discussing the ABR? What are the three different polarities used in ABR?

A

-The position of the speaker when it generates a sound
-The three different polarities are positive polarity (condensation), negative polarity (rarefaction) and the alternate polarity (combination of both)

42
Q

Which polarity is preferred for ABR testing?

A

-The alternate polarity is preferred to minimize the stimulating artifact
-The alternate polarity is a form of polarity that occurs when the rarefaction and condensation polarisations are administered successively

43
Q

How can noise be reduced from the ABR trace?

A

By selectively eliminating electrical activity outside the 30-3000 Hz range (energy of click ABR)

44
Q

How is the ABR impacted by the stimulus repetition rates?

A

-Need to do thousands of repetitions to extract ABR from noise
-If you speed up the repetition rates it decreases the test time which is good however you get a reduction in amplitude and increase in latency
-Need to allow some time for the auditory nerve to recover and refire
-Need robust waveform without taking too much time

45
Q

What are some examples of neurological problems the neurological ABR is useful for diagnosing?

A

-Retrocochlear lesions e.g. tumours on the auditory nerve, intra-axial tumours and tumours outside the brainstem
-Demyelinating disease e.g. MS
-Vascular lesions of the brain stem, blockages or haemorrhages of the blood vessels
-Differential diagnosis of comatose patients (e.g. metabolic or toxic cause vs structural lesion)
-Status of auditory nerve and brainstem pathways

46
Q

What can the ABR not diagnose?

A

The type of pathology e.g. vascular or tumour (can only indicate the possible existence of the retrocochlear lesion)

47
Q

Describe how the following sites of lesion affect which ear the ABR abnormalities manifest:
1. Auditory nerve lesion
2. Large CPA (cerebellopontine angle) tumours
3. Brainstem lesions

A
  1. Ipsilateral effects
  2. Contralateral effects due to brainstem compression
  3. Ipsilateral, contralateral or bilateral
48
Q

What is the procedure for neurological ABR testing?

A

-Intense stimulus level needed (between 60-90 dB HL)
-Must repeat to obtain at least 2 similar waveforms

49
Q

State the normal values for latency for each wave (neurological ABR)

A

Wave I- Smaller than 2 ms
Wave II- Smaller than 3 ms
Wave III- Smaller than 4 ms
Wave IV- Smaller than 5 ms
Wave V- Smaller than 6 ms

50
Q

How is the neurological ABR interpreted?

A

-Interpeak latency (interval between two waves) between waves I and V should be about 4 ms
-Compare between right and left sides
-IT5 (difference between wave V in right and left ear) useful when wave I is not able to be elicited

51
Q

What is the normal ratio of wave V to wave I (peak-to-peak amplitude of wave I and V)?

A

More than 1.0 uV

52
Q

What pathology may result in a very small wave V amplitude and a wave V/I ratio of less than 1.0 uV?

A

A retrocochlear pathology (problem with the auditory nerve)

53
Q

What may cause absent waveform components?

A

Lesions at the location/ primary generator site

54
Q

How do the following types of hearing loss affect the neurological ABR result:
1. Conductive
2. High-frequency sensory (cochlear)
3. Neural (e.g. acoustic neuroma)

A
  1. Good wave morphology, inter-peak latency with normal limits but waves I-V horizontally shifted (delayed)
  2. Small and poorly formed wave I, slightly delayed in latency, interpeak latency within normal limits, wave I disappears are stimulus intensity decreases, as the click-stimulus intensity level approaches threshold within the 1-4 kHz region, wave V latency increases sharply
  3. Clear wave I, normal latency, delayed inter-peak latency between wave I and III
55
Q

After obtaining which result from the PTA can you no longer use neurological ABR as part of your assessment?

A

If ABR is absent when there is a severe peripheral hearing loss

56
Q

Interpret these neurological ABR results which was carried out at 80 dB bilaterally

A

-Normal interaural differences
-Some individual wave latencies outside normal range bilaterally (slightly delayed latencies)

57
Q

How do you carry out threshold (audiological) ABR?

A

-Start at intensity which is loud enough to hear a response
-As intensity decreases, most ABR waves disappear except V which can be elicited within 10-20 dB of the behavioural threshold
-Continue to decrease until no wave V is seen

58
Q

What is the definition for ABR threshold?

A

The lowest level at which a CR is present with a RA recording at least 5-10 dB below the threshold, obtained under good recording conditions

59
Q

Define the terms in red present on this threshold ABR

A

CR= Clear response
RA= Response absent
Inc= Inconclusive (the wave is not repeatable enough and a conclusive decision cannot be made)

60
Q

Why should you take extra caution when trying to do ABR on patients with neurological damage?

A

-The results may be spurious (may interfere with the ABR itself so the results will not be helpful to us)
-Wave V may not be a valid indicator of peripheral hearing sensitivity

61
Q

If not hearing, what is ABR assessing?

A

The integrity of the peripheral auditory system and brainstem pathways before it reaches the cortex (means that cortically deaf patients will have normal ABRs)

62
Q

Which type of ABR should be used in medico-legal cases?

A

Threshold ABR

63
Q

Which type of ABR is used for diagnostics?

A

Neuro-otological

64
Q

Which waves are most important for threshold and neurological ABR?

A

Threshold- wave V
Neuro-otological- wave I to V

65
Q

What equipment is needed for ABR?

A

-Amplifier in order to amplify the small evoked potentials
-Two channel equipment
-Transducer- same options as PTA
-Biosense Medical AEP software

66
Q

What needs to be checked before the ABR testing begins?

A

-The parameters (transducer, which ear is being stimulated, polarity)
-The amplifier parameters (gain, artifact rejection, filter settings)
-Impedances (need to be below 5 kW and interelectrode impedances need to be balanced- difference between them cannot be more than 2 kW)

67
Q

How would you prep the patient’s skin and place the electrodes on them?

A

-Ensure the patient is comfortable lying down on a chair or a reclining couch
-Clean the skin with an abrasive gel
-Clean the higher forehead and behind the right and left ears on the mastoid
-Wipe abrasive gel in the same direction and then remove all the gel
-Place electrodes on the higher forehead as close to the hairline as possible, behind the left and right ears on the mastoid bone
-Once electrodes are in place put the transducer on

68
Q

How many sweeps does the ABR recording need to be run for?

A

The amount in the protocol

69
Q

What type of ABR is this? How would you interpret it and why?

A

-Neurological ABR- only one intensity tested on left ear (blue)
-Normal
-Normal latency for waves I, III and V, waveforms repeatable, waves I, III and V clearly visible

70
Q

What type of ABR is this? How would you interpret it and why?

A

-Threshold ABR- right ear tested
-Normal
-Stimulus level is decreasing, highly repeatable waveforms, threshold is 10 dB or better

71
Q

What type of ABR is this? How would you interpret it and why?

A

-Threshold ABR- broadband stimulus (click), different intensities tested
-Abnormal- severe or greater hearing loss
-No visible waveforms- response absent at 80 dB

72
Q

What type of ABR is this? How would you interpret it and why?

A

-Neurological ABR- only tested at one level
-Normal left ear, abnormal right ear- possible conductive hearing loss
-Good wave morphology but horizontal shift (delay)- prolonged latencies

73
Q

What type of ABR is this? How would you interpret it and why?

A

-Neurological ABR
-Abnormal- no waveforms present
-However no replications- needs to be replicated to be sure

Diagnostic Audiology (12 decks)

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