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Electrodiagnostics > BAER > Flashcards

BAER Flashcards

1
Q

Know ear anatomy

A

(slides 1-12)

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2
Q

Know the ascending central auditory pathway

A

(slides 12-16)
* Receptive organ: organ of corti
* 1° sensory neurons: bipolar cells. Dendrites = synapse with hair cells. Cell bodies =** spiral ganglion** (in bony cochlea). Axons = form cochlear nerve as leaving the cochlea.
* Dorsal and ventral cochlear nuclei (rostral medulla). DCN axons form the acoustic stria and join the contraolateral lateral lemniscus. VCN axons synapse on ipsi + controlateral dorsal nucleus of the trapezoid body.
* Lateral lemniscus (pons) bilaterally
* Caudal colliculis (midbrain): integration and reflex center
* medial geniculate nucleus (thalamus): relay center
* 1° auditory cortex (temporl lobe)

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3
Q

AERs represent the ____ latency components of auditory evoked responses

A

Early (0-10ms)

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4
Q

3 types of BAER stimuli

A
  • Air-conducted click
  • Ton-bip or burst
  • Bone-conducted click
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5
Q

Air-conducted clicks are square DC pulses at center frequency of ____ Hz, stimulating the ____ of the cochlea.

A

2-4 kHz, base (high f)

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6
Q

Tone-pip or burst: what’s it for?

A

Produces a narrow peak at a selected frequency, to stimulate a specific area of the cochlea. To assess sound sensitivity to various frequencies.

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7
Q

Bone-conducted click: what’s that?

A

Direct stimulation of the cochlea using a bone-stimulator. By-passes the middle ear. Useful to distinguish sensorineural vs conductive deafness.

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8
Q

What is the masking noise? what does it prevent?

A

Click delivered to controlateral ear. 20-30 dB lower intensity than stimulated ear. Goal: prevent the cross-over artifact

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9
Q

Describe anatomical placement of the 3 electrodes

A
  • Recording: vertex
  • Ground: nuchal crest (electrically neutral)
  • Reference: mastoid or dorsal spinous process of T1

slide 25

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10
Q

How to determine the BAER threshold (dB) of a patient?

A
  1. Set intensity level to a point where no BAER response is seen
  2. Increase by 5 dB increments until wave V appears (wave V threshold)
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11
Q

BAER is ____ of arousal level

A

independant (awake, sedated, GA)

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12
Q

Know the 7 BAER waveform generators

A

Slide 19

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13
Q

Normal BAER

How is hearing confirmed ?

A

Presence of 4-5 vertex-positive waves

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14
Q

Normal BAER

How to measure:
a) wave amplitude (uV)?
b) Absolute latencies (ms)?
c) Interpeak latencies (ms)?

A

a) +ve peak -> following -ve trough
b) stimulus -> +ve peak
c) peak-peak

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15
Q

Normal BAER

Wave I occurs within ____ ms latency

A

1-2 ms

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16
Q

What should we account for when measuring absolute latencies

A

0.9 ms delay from tubal insert

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17
Q

Which interpeak latencies are most commonly measured and what do they represent

A

I-III: dt from cochlear nerve -> pons
I-V: cochlear nerve -> midbrain

Slide 32

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18
Q

What is the central conduction time

A

Interpeak latency from I-V

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19
Q

Know the effect of mastoid vs T1 reference on waveforms

A

Slide 35

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20
Q

Wave IV is often merged with III or V with the ____ reference

A

Mastoid

M = merged

21
Q

Wave IV is generally a single peak with ____ reference

A

T1

1 = single

22
Q

Wave I latency is slightly longer with the ____ reference

A

T1 reference

(farther than mastoid)

23
Q

Name the 3 possible stimulus polarities

A

Rarefaction
Condensation
Alternating

24
Q

Which polarity better separates wave III and IV in dogs?

A

Rarefaction

Rare = the best

25
Which polarity produces the longest latency of wave I
Condensation | Longer word
26
What is the advantage of the alternating polarity
Reduces cochlear microphonics, stimulus artifact and distortion of wave I.
27
# Effect of ____ on waveform latencies and amplitudes ↑ intensity
↑amplitudes, ↓latencies | (intuitive)
28
# Effect of ____ on waveform latencies and amplitudes ↑ rate
↓amplitudes, ↑latencies | (opposite vs intensity)
29
# Effect of ____ on waveform latencies and amplitudes ↑ frequency (tone pip)
↓ latencies (sound travels from base -> apex of cochlea)
30
# Effect of ____ on waveform latencies and amplitudes Number of sweeps
↑ Signal-to-Noise ratio
31
# Effect of ____ on waveform latencies and amplitudes Anesthesia
Negligible (...) | more details slide 41
32
# Effect of ____ on waveform latencies and amplitudes Body T°
↑ latencies (flat line < 20°C)
33
# Effect of ____ on waveform latencies and amplitudes Head size
No effect
34
Which wave is the last to disappear with decreasing intensities
Wave V (1st to appear, last to disappear)
35
what happens if stimulus rate is too high (> 50/s)
Neural adaptation
36
Onset of hearing in a) Dogs b) cats c) LA
a) day 14 b) day 5 c) birth
37
When are Adult BAER waveforms reached in a) dogs b) cats c) LA
a) 4-6 weeks b) 6-8 weeks c) hrs after birth
38
# Abnormal BAER Structures affected with: a) Conductive deafness b) Sensorineural deafnesss c) Central deafness
a) External + middle ear b) inner ear + cochlear nerve c) brainstem + auditory cortex
39
# Abnormal BAER Waveform alterations for **conductive** deafness
* Flat line or delayed absolute latencies * Intact interpeak latencies * Restored with bone-conducted click
40
Waveform alterations for **sensorineural** deafness
* Flat line (complete loss) or delayed absolute latencies at low intensities (partial loss) * Intact interpeak latencies * NOT restored with bone-conducted click
41
Waveform alterations with **central** deafness
* Prolonged interpeak latencies (I-III, III-V, I-V), depending on site affected * > 0.2 ms latency difference between 2 ears * V/I amplitude ratio < 0.5 ms suggestive of brainstem Lx | Note: deafness requires extensive Lx
42
Which BAER waveform alterations are suggestive of **brain death**
Flat line +/- wave I and II preserved *isoelectric BAER + EEG confirms brain death for supratentorial Lx
43
# Deafness PSOM
Conductive *Restored with bone-conducted click | slide 50
44
# Deafness Otitis interna
Sensorineural | slide 51
45
# Deafness Congenital pigment-associated
Sensorineural, cochlear-saccular (stria vascularis) | slide 52
46
# Deafness Presbycusis
Sensorineural (hair cell abiotrophy) +/- conductive (ossicular OA) | slide 54
47
NIHL
Sensorineural (mechanical damage to hair cells) +/- conductive (damage to tympanic membrane) Causes a temporary or permanent threshold (wave V) shift (TTS, PPS) | slide 55
48
Ototoxicity
Sensorineural (cochlear saccular or neuroepithelial) | slide 56
49
Equine THO
Sensorineural (damaged cochlea) +/- conductive (damaged ossicles) *auditory loss is the most common neurological deficits, followed by vestibular and facial nerve dysfunction | Slide 58

Electrodiagnostics (10 decks)

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