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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
Q

Which polarity produces the longest latency of wave I

A

Condensation

Longer word

26
Q

What is the advantage of the alternating polarity

A

Reduces cochlear microphonics, stimulus artifact and distortion of wave I.

27
Q

Effect of ____ on waveform latencies and amplitudes

↑ intensity

A

↑amplitudes, ↓latencies

(intuitive)

28
Q

Effect of ____ on waveform latencies and amplitudes

↑ rate

A

↓amplitudes, ↑latencies

(opposite vs intensity)

29
Q

Effect of ____ on waveform latencies and amplitudes

↑ frequency (tone pip)

A

↓ latencies
(sound travels from base -> apex of cochlea)

30
Q

Effect of ____ on waveform latencies and amplitudes

Number of sweeps

A

↑ Signal-to-Noise ratio

31
Q

Effect of ____ on waveform latencies and amplitudes

Anesthesia

A

Negligible (…)

more details slide 41

32
Q

Effect of ____ on waveform latencies and amplitudes

Body T°

A

↑ latencies
(flat line < 20°C)

33
Q

Effect of ____ on waveform latencies and amplitudes

Head size

A

No effect

34
Q

Which wave is the last to disappear with decreasing intensities

A

Wave V
(1st to appear, last to disappear)

35
Q

what happens if stimulus rate is too high (> 50/s)

A

Neural adaptation

36
Q

Onset of hearing in
a) Dogs
b) cats
c) LA

A

a) day 14
b) day 5
c) birth

37
Q

When are Adult BAER waveforms reached in
a) dogs
b) cats
c) LA

A

a) 4-6 weeks
b) 6-8 weeks
c) hrs after birth

38
Q

Abnormal BAER

Structures affected with:
a) Conductive deafness
b) Sensorineural deafnesss
c) Central deafness

A

a) External + middle ear
b) inner ear + cochlear nerve
c) brainstem + auditory cortex

39
Q

Abnormal BAER

Waveform alterations for conductive deafness

A
  • Flat line or delayed absolute latencies
  • Intact interpeak latencies
  • Restored with bone-conducted click
40
Q

Waveform alterations for sensorineural deafness

A
  • Flat line (complete loss) or delayed absolute latencies at low intensities (partial loss)
  • Intact interpeak latencies
  • NOT restored with bone-conducted click
41
Q

Waveform alterations with central deafness

A
  • 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
Q

Which BAER waveform alterations are suggestive of brain death

A

Flat line +/- wave I and II preserved

*isoelectric BAER + EEG confirms brain death for supratentorial Lx

43
Q

Deafness

PSOM

A

Conductive
*Restored with bone-conducted click

slide 50

44
Q

Deafness

Otitis interna

A

Sensorineural

slide 51

45
Q

Deafness

Congenital pigment-associated

A

Sensorineural, cochlear-saccular (stria vascularis)

slide 52

46
Q

Deafness

Presbycusis

A

Sensorineural (hair cell abiotrophy) +/- conductive (ossicular OA)

slide 54

47
Q

NIHL

A

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
Q

Ototoxicity

A

Sensorineural
(cochlear saccular or neuroepithelial)

slide 56

49
Q

Equine THO

A

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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