VEMPs Flashcards
1
Q
very basic what are vemps
A
electrical recordings produced by a muscle in response to a stimulus processed by the vestibular system or at least by a portion of it
2
Q
history of VEMPS
A
- short latency myogenic responses were recorded to loud clicks with active electrode below the inion
- vestibular origin questioned
- new recording method from neck flexor muscles
3
Q
how do we know there is a vestibular input and that it is not mediated by the cochlea
A
- know there is a vestibular origin because the response is aboloshed following unilateral vestibular neurectomy
- know it is not from the cochlea because there is no correlation between response and degree of SNHL
- –if there is CHL, there will not be a VEMP
4
Q
sternocleidomastoid muscle origin, insertion, and action
A
- origin (2 heads):
- –top of the sternum
- –middle portion of the collarbone (clavicle)
- insertion:
- –mastoid process of the temporal bone (located behind the ear)
- action:
- –laterally flexes to the side of the contracted muscle (ear touching shoulder)
- –rotates to the opposite side of the contracting muscle (chin pointing up in opposite direction)
- –when both are contracted, the neck flexes (chin tuck position)
- –aides in deep breathing
5
Q
normal latency for VEMPs
A
seen within 20-25ms
6
Q
what are the two components of a VEMP response
A
- P1 which is positive
* N1 which is negative
7
Q
what is the saccule
A
- vertically oriented in the sagittal planes (divides left and right)
- hair cells oriented with the kinocillium (excitation) away from the striola
- forces on the saccule:
- –parallel=causes shear force=stimulation
- –perpendicular=compressive=non-stimulating
- linear accelerometer
- note: the saccule is the receptor for sound and vibration in some amphibians
8
Q
cVEMP pathway summary
A
- sound stimulates the saccule
- traverses the vestibular nerve and ganglion to reach the vestibular nucleus in the brainstem
- from there, impulses are sent to the neck muscles via the medial vestibulospinal tract (MVST) and the leg muscles via the lateral vestibulospinal tract (LVST)
- sound evoked VEMPs are almost completely unilateral
9
Q
patient preparation for VEMPs
A
- requires the pt will lie flat or sit upright and still for a few minutes
- skin is cleaned on the forehead and on the neck
- electrodes are placed over the cleaned surface
- headphones are positioned
10
Q
recording method for VEMPs
A
- sternocleidomastoid muscle activated and high-level acoustic stimulus presented
- side of SCM muscle activation vs stimulus ear
- –unilateral vs bilateral SCM muscle activation
- —–need a 2 channel setup for bilateral stimulation
- —–shortens test time, which may be helpful for peds or elderly
- –ipsilateral, contralateral, and binaural stimulation
- have pt lying or sitting with SCM muscle contracted, then deliver sound
- SCM muscle contraction will change (transient) because pt gets fatigued
11
Q
parameters with 500 Hz tone burst evoked VEMPs
A
- onset phase: rarefaction
- level: 90-95 dB nHL
- rate: 5/second
- rise/fall: 2 cycles
- plateau: 0 cycles
- gating: blackman
12
Q
parameters with click evoked VEMP
A
- polarity: rarefaction
- level: 90-100 dB nHL
- rate: 5/second
- duration: 100 microseconds
13
Q
recording parameters of VEMPs
A
- amplifier gain: 5000x
- filter settings: 10-1000Hz
- time window: 100 msec
- # of sweeps: 64-256
- artifact rejection: off
- number of channels: 1-2
- non inverting electrode: mid sternocleidomastoid muscle
- inverting electrode: sternoclavicular junction
- ground electrode: forehead
14
Q
general latency of P1 for VEMPs and N1 latency
A
- 13-19ms for P1
* N2 latency 20-28ms
15
Q
clinical uses of VEMPs
A
- cVEMP reflects stimulation of the saccule, a vestibular end organ not evaluated by typical vestibular testing
- oVEMP reflects the utricle
- VEMP evaluated neural pathways not measured in those recording the VOR
