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Electrophysiology > ABR - Diagnosis > Flashcards

ABR - Diagnosis Flashcards

1
Q

Evoked potentials definition

A

electrical signals generated by the nervous system in response to a stimulus

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2
Q

What are 2 short-latency evoked potentials?

A

ECochG and ABR

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3
Q

In general, what is the ABR (auditory brainstem response)?

A

a relatively quick and reliable, objective clinical test that measures the functional integrity of the auditory peripheral and brainstem structures (tests from the cochlea to the brainstem)

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4
Q

ABR is probably the most widely used AEP in which clinical scenarios?

A
  • estimating behavioral thresholds in infants
  • detecting neurologic abnormalities of the VIII CN and brainstem
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5
Q

The important thing to remember about the ABR is that it…

A

makes INFERENCES about hearing (it’s not an actual hearing test!!)

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6
Q

What type of stimulus does the ABR test protocol typically use?

A

clicks

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7
Q

How does the ABR actually measure hearing?

A

it measures hearing based on the electrical output from the different structures along the auditory pathway

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8
Q

What are the 3 main categories of clinical applications for the ABR?

A
  1. hearing screening (for early ID of HL)
  2. estimation of hearing thresholds
  3. neuro-otologic applications
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9
Q

What are some examples of neuro-otologic applications of the ABR?

A
  • determining site/level of a lesion
  • monitoring of comatose patients
  • intraoperative monitoring
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10
Q

Describe the morphology of the ABR.

A

a series of + and - peaks (biphasic) of waves (components) after the onset of a high-intensity, brief stimulus (click)

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11
Q

How are the components of the ABR typically identified/labeled?

A

with Roman numerals; I-VII

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12
Q

T/F: At higher intensities, all ABR components are visible with wave V being the largest.

A

True

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13
Q

What are the characteristics of waves II, IV, VI, and VII?

A

they’re typically smaller and quite variable, and can’t always be recorded in all patients (thus limiting their clinical application)

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14
Q

Which waves of the ABR are usually analyzed for diagnostic purposes?

A

waves I, III, and V

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15
Q

What are 3 types of stimuli the ABR can use?

A
  • clicks
  • chirps
  • tone bursts
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16
Q

Characteristics of click stimuli:

A
  • abrupt onset
  • short duration
  • broad spectrum (to evoke responses from numerous nerve fibers along the cochlear partition)
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17
Q

What is the range of sound that click stimuli usually evaluate?

A

2000 to 4000 Hz

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18
Q

Characteristics of tone burst stimuli:

A
  • provide fx specific info
  • requires a longer recording window to capture specific responses
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19
Q

What is an example of a clinical scenario where you would use tone burst stimuli in an ABR?

A

when building a baby’s audiogram to determine thresholds for cochlear implantation

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20
Q

Why do tone burst stimuli require a longer duration for recording?

A

because the response has a longer latency in comparison to click stimuli

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21
Q

Characteristics of chirp stimuli:

A
  • more efficient than clicks because it evokes larger amplitude ABRs
  • this advantage is dependent on cochlear fx specificity
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22
Q

Testing parameters for chirp stimuli:

A

either fx specific, or in a 2000 to 4000 Hz range

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23
Q

What is the reason the ABR can be used to determine the site/level of a lesion?

A

the ABR waveform reflects the neural activity that originates in the different anatomical structures along the neural pathway

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24
Q

Wave I of the ABR correlates to which structure?

A

the part of the auditory nerve closest to the cochlea

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25
Q

Wave II of the ABR correlates to which structure?

A

the part of the auditory nerve closest to the brainstem

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26
Q

What are two terms we use to describe an ABR waveform?

A

latency and amplitude

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27
Q

What are the two types of latency in reference to ABR testing?

A

absolute and relative

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28
Q

Absolute latency definition

A
  • the neural conducting velocity, essentially, how fast a stimulus is passing through the anatomical structure
  • on the waveform, it’s where each peak appears (I, II, III, etc.)
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29
Q

Relative latency definition

A

consists of inter peak latency and intramural latency differences

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30
Q

Interpeak latency definition

A

the latency between waves, such as I-III, III-V, or I-V

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31
Q

interaural latency difference definition

A

comparison of the right vs left side of the brain

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32
Q

What are some factors that affect amplitude of ABR waveforms?

A
  • temporal synchrony/neural activity coherence in the responding structures
  • the number of elements contributing to the response
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33
Q

A smaller amplitude of an ABR wave signifies…

A

lower temporal synchrony

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34
Q

A larger amplitude of an ABR wave signifies…

A

a greater number of neurons being activated

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35
Q

What is the amplitude ratio of Wave V to wave I typically used for in clinical scenarios?

A

because wave V is typically larger than wave I, any low ratio may be indicative of a pathological abnormality

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36
Q

In regards to latency of waveforms, what two components appear to generate waves I and II of the ABR?

A

the auditory nerve (distal and proximal portions respectively)

37
Q

In regards to latency on waveforms, what component appears to generate wave III?

A

the ipsilateral cochlear nucleus

38
Q

In regards to latency on waveforms, what component appears to generate wave IV?

A

the superior olivary complex

39
Q

In regards to latency on waveforms, what component appears to generate wave V?

A

the rostral part of the contralateral Lateral Lemniscus, proximal to its termination in the inferior colliculus (the LL inputs to the contralateral IC)

40
Q

What are 4 stimuli factors that can affect ABR waveforms?

A
  • intensity
  • frequency
  • stimulation rate
  • polarity
41
Q

Characteristics of intensity of a stimulus

A
  • influences latency and amplitude
  • a change in intensity affects waves I-IV most prominently, while wave V becomes more robust
42
Q

An increase stimulus intensity results in…

A

a decreased latency

43
Q

A decreased stimulus intensity results in…

A

an increased latency

44
Q

Amplitude and stimulus intensity are directly proportional, meaning…

A

increased intensity will increase the amplitude (and vice versa)

45
Q

Characteristics of frequency of a stimulus

A
  • tone burst and chirps are fx specific
  • the absolute latency should decrease as the fx increases
  • wave V is easily IDed in all 4 fxs (500, 1k, 2k, 4k Hz)
  • waves I and III are only IDed in 2k and 4k Hz
46
Q

Characteristics of the rate of a stimulus

A
  • repetition rate = rate at which stimuli are presented in a time unit
  • changing of rate is used to evaluate the nature of neural adaptation
  • increased presentation rate increases latency, and reduces amplitude of all components
47
Q

Why do we want to evaluate neural adaptation in ABR through presentation rates of stimuli?

A

this value could be different in normal hearing patients vs those with auditory nerve or brainstem pathologies (good for diagnostics)

48
Q

Characteristics of polarity of a stimulus

A
  • rarefaction = neural activity occurs about half a period earlier when compared with condensation; latency is also shorter
  • alternating = can be used to eliminate/reduce stimulus artifacts at high stimulus levels
49
Q

Studies show that rarefaction produces…

A

more robust and shorter latency, thus increasing auditory sensitivity

50
Q

Studies show that stimuli of condensation elicit…

A

earlier responses

51
Q

Analog filtering is performed on the input signal to accomplish what for ABR?

A

to remove frequency components that are not part of the signal of interest

52
Q

What filter setting is commonly used for supra threshold measures in ABR?

A

band-pass setting of 100 - 3000 Hz

53
Q

What filter setting is commonly used for measures near threshold in ABR?

A

usually a more open, band-pass setting of 30 or 50 to 3000 Hz is used (this helps to capture the broad, lower-fx wave V near the threshold)

54
Q

What kind of impedance readings are necessary for obtaining quality ABR waveforms?

A

low (below 5 kiloOhms) and balanced

55
Q

What should the value of the inter-electrode impedance be for obtaining quality waveforms?

A

when the values are within 2k Ohms of each other

56
Q

Why do contralateral waveforms not display wave I?

A
  • because they don’t activate the auditory nerve ( they only display waves III-VI)
  • it also enhances wave V
57
Q

What causes a post-auricular muscle artifact (PAM)?

A

contraction or movement of muscles located behind the ear, particularly the post-auricular muscles

58
Q

What type of masking is used for ABR, typically?

A

white noise, since the click is a broadband stimulus

59
Q

How much masking would be needed during an ABR test?

A

it has to be enough to elevate the hearing threshold in the non-test ear; this prevents cross over of the signal

60
Q

T/F: Masking affects the latency or amplitude of an ABR response.

A

false

61
Q

ABR masking conditions for AC

A

if the latencies of waves I and V are abnormal, then you need to mask

62
Q

ABR masking conditions for BC

A

if wave I is absent or delayed, masking is needed

63
Q

A caudal to rostral course of maturation means what?

A

that the auditory nerve matures before the brainstem

64
Q

Newborn ABR morphology

A
  • characterized by 3 prominent, almost equal amplitude peaks as early as 32 weeks conceptional age
  • emergence of other components occurs by about 3 months of age
65
Q

The absolute latencies of waves III and V continue to decrease with little change in wave V’s absolute latency after how many weeks?

A

40

66
Q

When does Wave I latency reach adult values?

A

as early as 3 months old

67
Q

When does wave V and IPLs reach adult values?

A

they continue to decrease and reach adult values by 18-24 months

68
Q

ABR latencies continue to … throughout early childhood before … and then start to … as we age.

A

decrease; stabilization; increase

69
Q

The amplitude of wave I has been reported to decrease with what 2 factors?

A

age and HL

70
Q

Female ABRs consistently show…

A

shorter absolute latencies, and larger amplitudes throughout waves III-V (in comparison to males)

71
Q

What are some other factors that are included in gender differences between ABR waveforms?

A
  • hearing sensitivity
  • body temperature
  • smaller head size
  • smaller brainstem distances
  • hormonal differences
72
Q

Small changes in body temperature can impact neural activity by…

A

influencing the events that lead to action potential generation, neurotransmitter release, synaptic transmission, and neural conduction velocity

73
Q

T/F: An ABR screening is recommended for babies needing care in the NICU for more than 5 days.

A

True (they could be at risk for late-onset progressive HL or ANSD)

74
Q

The JCIH recommends that a repeat screening be performed under what circumstances?

A

if the infant doesn’t pass the initial screening before hospital discharge (preferably several hours after the first)

75
Q

When does ABR indicate brain death in comatose patients?

A
  • when wave I is present by itself
  • when the absence of wave I is accompanied by a documented auditory end organ injury
  • when previously recorded potentials are no longer detectable
76
Q

Reasons to use ABR for intraoperative monitoring

A
  • hearing preservation (for procedures near the auditory system)
  • having the info can be handy when discussing postoperative outcomes for hearing
  • establishing preoperative baselines
  • continuous monitoring of neural functions in auditory structures during the procedure
77
Q

Hearing is often considered at risk during procedures concerning lesions in which area of the brain?

A

the cerebellopontine angle area

78
Q

AEP testing during surgical procedures can also help do what?

A

facilitate development and improvement of surgical techniques

79
Q

List the components for clinical interpretation of ABR.

A
  • identification of waveforms (presence or absence of waves I, III, and V)
  • latencies of waves I, III, and V
  • inter peak intervals of I-III, III-V, and I-V
  • right left differences of the inter peak intervals
  • amplitude ratio of IV/V:I
80
Q

ABR that could indicate conductive HL

A
  • all waves’ absolute latencies would be delayed
  • inter peak intervals would still be normal
81
Q

ABR that could indicate SNHL

A
  • mild HL would present with reduced amplitudes (anything worse, they’d be decreased further/absent)
  • some waves might still be present
  • normal latencies
82
Q

What are the norms for latency of waves I, III, and V?

A

I = 2.06 ms, III = 3.57 ms, V = 5.53 ms

83
Q

What are the norms for inter peak intervals of waves I, III, and V?

A

I-III = 1.51 ms, III-V = 1.96 ms, I-V = 3.47 ms

84
Q

ABR criteria for retrocochlear dysfunction

A
  • absence of all waves I-V that are unexplained by extreme HL determined by audiometric testing
  • absence of all waves following I, II, or III
  • abnormal prolongation of inter peak intervals I-III, III-V, and I-V
  • abnormal diminished V/I amplitude ratio, especially when accompanied by other abnormalities
  • abnormally increased differences between the 2 ears (interaural differences) when not explained by unilateral or asymmetric middle and/or ear dysfunction
85
Q

Audiometric profile for patient with an acoustic neuroma

A
  • higher fx hearing loss usually occurs first
  • unilateral loss
  • tinnitus and/or dizziness on one side
  • SRT fine
  • WRS not consistent with pure tones
86
Q

Abnormalities of Wave I on ABR can indicate…

A
  • peripheral auditory dysfunction (conductive or cochlear)
  • pathology involving the distal auditory nerve
  • intracranial pathology due to the cochlea receiving blood supply from the internal auditory artery
87
Q

What condition can be indicated by a poorly formed/absent wave I, but a clear wave V?

A

high-frequency HL

88
Q

Indications of abnormal I-III inter peak intervals

A
  • prolongation reflects dysfunction between the auditory nerve and the lower pons (on the stimulated side)
  • acoustic neuromas
  • demyelinating disease
  • brainstem tumors
  • vascular lesions on the brainstem
89
Q

Indications of abnormal III-V inter peak intervals

A
  • reflects dysfunction between the lower pons and mesencephalon (usually, but not always, on the ipsilateral side to the lesion)
  • demyelinating disease
  • tumor
  • vascular disease

Electrophysiology (5 decks)

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