Vestibular Foundations - VEMP Part 2

cVEMP= saccule
oVEMP= utricle

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

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

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

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

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

• 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.

-cervical spine problems

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

-hyperacusis and tinnitus as it can aggravate these

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

equally tense their neck on both sides

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

500Hz

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

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

• 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

-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

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

Right vs Left

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

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

we calculate the Asymmertry Ratio (AR) or Saccular Paresis

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

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

• 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.

no 80, 70 is too low. 95 is good

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

• 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.

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

Check the asymmetry ratio between left and right ear

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