· The purpose of this test is to determine if the saccule, one portion of the otoliths, as well the inferior vestibular nerve and central connections, are intact and working normally. The saccule, which is the lower of the two otolithic organs, has a slight sound sensitivity and this can be measured.
· VEMPs are recorded using an evoked response computer, a sound generator, and surface electrodes to pick up neck muscle activation or other muscles if this is of interest.
VEMP testing is not hard, but there are a lot of technical pitfalls.
· It is a very big response, and as long as the person doing the test is attentive to details (getting the sound in both ears with proper placement of inserts or headphones, having the person lift their head through the entire trial, electrodes in the right place with proper impedance), it is very straightforward.
- Best practice, subjects are instructed to tense the muscle during runs of acoustic stimulation, and relax between runs. If the neck muscles are not activated, no VEMP is produced. The reflex scales to tonic EMG — once again — if you don’t activate the neck muscle, you don’t get a response.
- Some patients are unable to hold their heads up. In this case, some experts recommend simply tilting the entire body up by about 30 degrees, so that there is less torque needed by the patient to hold their head up.