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Vestibular Foundations > Session 7- VEMP > Flashcards

Session 7- VEMP Flashcards

1
Q

how do we measure the function of the utricle and the saccule organs?

A

using VEMP

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2
Q

how many types of VEMP are there?

A

1=cVEMP is recorded from the neck (sternocleidomastoid muscle ) and measures the function of the saccule and inferior vestibular nerve

2=oVEMP is recorded from the eye and reflects primarily utricular function

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3
Q

what does cVEMP stand for?

A

Cervical Vestibular Evoked Myogenic Potential

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4
Q

how do we elicit (evoke) cVEMP?

A

by using either:
-acoustic
-vibratory
-galvanic

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5
Q

what is the most common method of recording cVEMP?

A

-using an acoustic stimulus, either a 2-1-2 or 2-2-2 tone burst at a loud intensity usually at around 95dBnHL

  • the response is then recorded by using surface electrodes at fore-cites at the head and neck
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6
Q

what is the most common electrode montage for cVEMP?

A

is to record from the clavicular joint, forehead and each sternocleidomastoid muscle

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7
Q

what is it important for the patient to do to record a cVEMP?

A

to maintain a contracted sternocleidomastoid muscle.

  • the patient is instructed to either turn their head left or right depending on which side is stimulated
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8
Q

how can a patient monitor their muscle contraction?

A

-visually by using a patient ENG monitor or audibly by using a ENG monitor tone

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9
Q

How is the cVEMP represented?

A

by 2 dystinct peaks. P1 occurs at approximately 13 milli seconds and N1 at approximately 23 milli seconds

p13n23 comples, anything after n23, is cochlear in origin so ignore

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10
Q

what is the purpose of the cVEMP?

A

its a clinical method of assessing the integrity pf the saccule, inferior vestibular nerve and VCR pathway in humans

  • it forms an ipsilateral waveform response generated by activation of vestibular afferents.
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11
Q

what does the latency of the cVEMP waveforms depend on?

A

the design and stimulus chosen to elicit the cVEMP

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12
Q

how do we ensure even muscle contraction?

A

using ENG scaling (Amplitude normalisation)

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13
Q

how is the amplitude, latency and threshold be analysed/ measured?

A

using cVEMP

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14
Q

What ratio is used in cVEMP testing to detect vestibular dysfunction?

A

the amplitude ratio between the right and left ears

a difference greater than 36% is indicative of vestibular dysfunction

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15
Q

what can cVEMP be used for?

A

can detect Superior semicircular canal Dehiscence, Saccular Dysfunction as well as disorders of the Inferior Vestibular Nerve

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16
Q

What is VNG used for?

A

to asess vestibular and occular motor function VOR

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17
Q

what is vHIT used for?

A

to assess function of all 6 semi-circular canals

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18
Q

what does oVEMP stand for?

A

Ocular Vestibular Evoked Myogenic Potential

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19
Q

which muscle is the oVEMP measured from?

A

the evoked potential is measured from the Inferior Oblique muscle

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20
Q

Which vestibular structures and nerve does the oVEMP test primarily depend on?

A

its largely dependent on the utricle and the superior vestibular nerve

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21
Q

what kind of stimulus evoke the oVEMP?

A

-Acoustic (most common)
-Vibratory
-Galvanic

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22
Q

what is the most common method of recording oVEMP?

A

-using an acoustic stimulus using a 2-2-2 tone burst at a loud intensity usually at around 95dBnHL

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23
Q

what is the most common electrode montage for oVEMP?

A
  • the response is then recorded by using surface electrodes at fore-cites at the Underneath each eye, Chin, Forehead (Ground).

the oVEMP is largest when recorded contralaterally which is why the right reference electrode is placed underneath the left eye.

24
Q

what is the patient positioning and instructions for oVEMP?

A
  • patient should be seated or reclined
  • maintain a upwards gaze of 35 degrees for the duration of the recording
25
Q

How is oVEMP represented?

A

by 2 distinct peaks. N1 occurs at approximately 10 milli seconds and P1 at approximately 15 milli seconds

  • you do the tone presentations for the 100-150 times, we do a weighted add, where it adds these results together and gives an average of them
26
Q

what information can be interpreted with the oVEMP?

A

-amplitude
-latency
-threshold

27
Q

what is the most robust ratio to analyse with oVEMP?

A

Amplitude ratio between right and left ears.

A difference of >33% is a sign of dysfunction

28
Q

What is the benefit of combining oVEMP with other vestibular tests like vHIT and VNG

A

it helps assist diagnose:
- SSCD (superior SemiCircular Dehiscence)
- Meniere’s Disease
-disorders of the superior superior vestibular nerve

29
Q

what does VEMP stand for?

A

Vestibular - comes from the vestibular system (sound evoked stimulus via air conduction- patients don’t have to hear the sound

Evoked- in response to a stimulus

Myogenic- its a muscle response that we are recording

Potential- we place electrodes on the skin to record this muscle changes

30
Q

what part of the structure for VEMPs test?

A

the otolith organs

31
Q

what otolith organ is being tested with each VEMP test?

A

cVEMP= saccule
oVEMP= utricle

32
Q

what happens with a cVEMP?

A

1- play a aloud air conduction stimulus to the ear

2- this stimulates the primary afferents of the saccular macular

3- info is relayed along the inferior vestibular nerve up to the vestibular nuclei

4- the info reflexed down the vestibular spinal tract via the vestibular colic reflex

5- its contracts the SCM in the neck

6- we record a change in the tonicity of the muscle

33
Q

is the cVEMP and ipsi or contralateral test?

A

its a ipsilateral, you play the sound in the left ear, the left muscle contracts

34
Q

for a cVEMP test, does the patient need to hear the stimulus?

A

no, the sound creates a travelling wave of pressure that stimulates the otolith organs

35
Q

how does the oVEMP work?

A

1- stimulus comes from the utricle, travels along the superior vestibular nerve to the vestibular nuclei

2- neural signals crosses over the mid line and uses the VOR (vestibular ocular reflex)

3- as it comes down to the eye muscles, we record the muscle tonicity in the extraocular muscle

36
Q

is the oVEMP and ipsi or contralateral test?

A

this is a cross response, stimulus the left ear, we record the muscle tonicity in the right eye muscle BUT its still testing the left ear

37
Q

what are the differences between the cervical VEMP and the ocular VEMP?

A
  • Cervical VEMP:
  • believed to come from the Saccule
  • travels along the inferior vestibular nerve
    -the reflex is measures at the Sternocleidomastoid muscle
  • Its an inhibitory response
  • Its ipsilateral

*Ocular VEMP:
- believed to come the Utricle (depending the stimulus used)
- travels along the Superior vestibular nerve
- Reflex is measured at the Extraocular muscle
- Its an Excitatory response
-Its Contralateral

=oVEMPS are really easy to record but the oVEMP is really hard to record.

38
Q

what are cVEMP contraindications?

A

-cervical spine problems

-conductive hearing loss- because the sound isn’t conducted throughout the ear

-hyperacusis and tinnitus as it can aggravate these

39
Q

what are the steps for measurements of cVEMPs?

A

1- use nuprep to remove any dead skin cells

2- place an electrode on the forehead

3- place the active electrode on the midpoint of the SCM on the neck

4- place the reference electrode on the sternoclavicular joint (bit above the collar bone)

5- tell patient to active the sternocleidomastoid muscle (tonicity of this muscle directly affects how big our recordings are.

6- present a high level acoustic stimulus approximately 95 dBnHL to ipsilateral ear

7- use a very short tone burst, because ts so short in duration, it doesn’t sound uncomfortable

40
Q

what do we need to ensure the patient does so that we can compare cVEMP recordings on each side?

A

equally tense their neck on both sides

40
Q

how does the patient activate the neck muscles (sternocleidomastoid) ?

A

tell the patient to lie down flat and lift their head

or you can push the patients head and they use their forehead to push your hand away

-or MOST COMMONLY turn your head 45 degrees to the side you’re not testing and dip your ear towards the floor

*hold the position for about 45 seconds

41
Q

for cVEMPS, which frequency has the largest reponse?

A

500Hz

42
Q

how do we record cVEMPs?

A

100-150 sweeps (30-40 seconds). We do this once, let the patient rest and do it again.

  • then we do a weighted add, where it adds these results together and gives an average of them
43
Q

why do we record cVEMPs unilateral?

A

because there’s a cross response that we don’t want to be interpreting

so, we ensure equal EMG activity is maintained for both the left and right sides to allow accurate comparisons

44
Q

what are some common pitfalls for cVEMPs?

A
  • conductive hearing loss: an air-bone gap as small as dB can effect recordings as the stimulus is too quiet so we don’t get the travelling wave for them.
  • we don’t get the patient to tense their neck enough, the more tense the neck, the better the recording.
  • stimulus too quiet
  • insufficient muscle tonicity
  • electrode placement
45
Q

what kind of stimuli can be used to elicit a cVEMP or oVEMP response and why the different stimuli?

A

-Both oVEMPs and cVEMPs can be elicited in response to air conduction, bone conduction and electrical stimuli.

*Reasons for different stimuli:
- clinical differentiation between retrolabryinthine and labyrinthine lesions.
- AC cVEMP responses were lose in subjects with air-bone gaps as small as 8.75

46
Q

what is interaural amplitude comparison

A

just work out whether the waveform on the right side and the waveform on the left side are the same size.

Right vs Left

47
Q

How do you interpret cVEMP and oVEMP tracings?

A

1-is there a presence of a waveform. flat line is no VEMP response

2- if you get the presence of a waveform on both sides, compare which is larger vs smaller

48
Q

what does a VERY late latency suggest?

A

some kind of central pathology but we don’t really use latency to interpret VEMPs

49
Q

how do we know if the level of asymmetry is abnormal?

A

we calculate the Asymmertry Ratio (AR) or Saccular Paresis

  • most commonly 40% + difference between R & L VEMP response is abnormal
50
Q

what is the clinical use of VEMPS

A

NOT EVERYONE HAS ACCESS TO THIS EQUIPMENT but we use it for:

  • patients with complaint of sound- evoked vestibular symptoms
  • these patience often have SCCD (Dehiscence- the thinning or disappearance of the temporal bone(bony labyrinth) , makes them dizzy as it creates an extra window on top of the oval window )
  • assessment of the otoliths and vestibular nerve to identify vestibular pathologies (e.g. acoustic neuroma), such as Meniere’s disease or vestibular neuritis
51
Q

What kind of VEMPs would someone with Superior canal dehiscence syndrome have?

A
  • they get VEMPs at very low levels that we would expect VEMPs to be obliterated at.
  • Dehiscence of the bony labyrinth and development f a third window in the superior semicircular canal.
  • VEMP abnormalities can be used in the diagnosis of SCDS
  • Pathological hypersensitivity to sounds will result in high amplitude Reponses to low threshold stimuli (70dBnHL or below) in repose to both AC and BCV stimulation.
52
Q

would a normal person have VEMPS around 80?

A

no 80, 70 is too low. 95 is good

53
Q

what do peak latency delays tell us

A

Peak latency delays can be used to signify retrolabyrinthine or central
pathologies

54
Q

What is the asymmetry ratio (AR) in VEMPs, and what is its clinical significance?

A
  • The asymmetry ratio (AR) measures the difference in VEMP amplitudes between the right and left sides.
  • Values greater than 40% are typically considered abnormal.

-Indicates possible unilateral vestibular dysfunction, such as:
Saccular paresis (saccular dysfunction).
Inferior vestibular nerve abnormalities.

55
Q

what is the calculation for asymmetry?

A

LA-SA/ R+L

LA- larger of the left or right amplitude
SA- smaller of the left or right amplitude
R- right amplitude
L- left amplitude

56
Q

How to tell if there is an abnormality in oVEMP results

A

Check the asymmetry ratio between left and right ear

If there is a difference of more than 33% there is dysfunction

Vestibular Foundations (10 decks)

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