Rotary Chair, VAT, VHIT

Question 1

rationale behind rotary chair testing

Answer 1

• rotational testing has historically been utilized to view:
• –per-rotary nystagmus=during rotation
• –post-rotary nystagmus= following rotation
• ENG/VNG is limited in that stimulation of lateral canal occurs in lower frequency region
• there may be mild spontaneous/positional nystagmus in the presence of normal calorics
• –may indicate compensation
• rotational chair testing may supplement this info
• may be a milder stimulus
• may expand evaluation and help assist in determination of peripheral vs central

Question 2

suggestions for use of rotary chair testing

Answer 2

• expand knowing the status of peripheral vestibular system and compensation
• when spontaneous/positional nystagmus has resolved, but unilateral weakness and symptoms still exist
• to evaluate extent of bilateral weakness
• when caloric irrigations may not be reliable or available (TM perfs, atresia)
• when results are below 10 degrees/sec (hypofunction)
• when a baseline is needed prior to treatment
• –meniere’s
• –chemical ablation (gentamicin treatments)
• can make impact upon course of rehab program
• especially in pts with bilateral peripheral loss
• may be normal and confirm artifact with pts demonstrating mild caloric abnormality
• may be rotary chair or SHA (sinusodial harmonic acceleration)

Question 3

rotary chair testing test protocols

Answer 3

• computer control and analysis have been added to existing tests
• may now obtain frequency specific info
• each stimulus affects both sides simultaneously since we all have a push-pull mechanism
• may either use EOG or VOG (electrodes or frenzels)
• are evaluating VOR: slow component of jerk nystagmus
• –darkened enclosure and tasking is crucial
• projection of eye onto tv screen with VOG so it can be observed by examiner
• assumption: when chair moves, head is making the same movement
• –this assumption may be faulty with frequencies greater than 1 Hz
• restraints:
• –harness, seatbelt
• –ankle straps
• –head restraints
• test frequencies from 0.10 Hz- 1.28 Hz (not descrete frequencies, but octave intervals)
• usually start with lower freqs
• octave intervals
• –0.01, 0.02, 0.08, etc
• signal averaging
• multiple cycles of a given frequency
• –many cycles allow for averaging to minimize artifact and increase test.retest reliability

Question 4

test paradigm for Rotary Chair testing

Answer 4

• slow component eye velocity added to subsequent responses and divided by # of cycles
• –so if 15+16+13+18, divided by # of cycles, similar to averaging of caloric response
• greater number of cycles to average allow for increased reliability
• not all frequencies are tested on all pts
• low frequencies: weakest response from VOR
• –also greatest nausea
• some clinics begin at 0.08 Hz and reduce to 0.01 Hz
• –then proceed from 0.16 Hz to 0.64 Hz

Question 5

step testing for rotary chair testing

Answer 5

• 100-200 degrees per second
• acceleration is done in steps
• VOR response is noted as per rotary (during rotation)
• important measure: time constant is reported in seconds

Question 6

time constant (TC) measure in rotary chair testing

Answer 6

• when the cupula is defected, it takes about 7 seconds to respond and this is lengthened by the storage velocity system (central)
• –central velocity storage: lengthens the cupula deflection from peripheral system from 7 sec to 13-14 sec
• upon acceleration, nystagmus increases and as reach a constant frequency, nystagmus decreases
• TC: time it takes for nystagmus to diminish to 37% of its original strength

Question 7

what pt perceives during step testing

Answer 7

• pt falsely perceives that chair is slowing down
• tasking and head stabilization are crucial
• time constants less than “norm” may be indicative of peripheral vestibular system dysfunction
• note: it is important to attain norms in your own clinic for all vestibular measures

Question 8

another definition of time constant with regards to step testing

Answer 8

• TC: timing relationship between head movement and subsequent eye movement response
• after 45-60 seconds, deceleration step is applied and chair stops
• nystagmus beats in opposite direction and is called post rotary
• upon chair’s stopping, pt perceives that chair is moving on opposite direction
• another time constant is measured related to time in seconds for decay of nystagmus

Question 9

interpretation of rotary chair testing

Answer 9

• 3 measurable parameters from rotary chair testing:
• –phase
• –gain
• –asymmetry

Question 10

phase as a rotary chair measure

Answer 10

• timing between head and eye movement
• eyes are not exactly 180 degrees out of phase with head movement
• eye movements may lead the head= phase lead
• amount is phase angle, measured in degrees
• increase in phase lead outside of normative ranges (+/- 2 standard deviations) implies abnormally short TC
• –problem with “timing”
• shortened TC may indicate peripheral disorder
• velocity storage arises from vestibular nuclei
• –damage in vestibular nuclei may result in lower TC
• need to take into consideration all test findings
• low phase lead may result in abnormally high TC, which may indicate a cerebellar disorder

Question 11

gain as a measure of rotary chair testing

Answer 11

• gain=measure of overall responsiveness of system
• slow component velocity of eye/velocity of head
• may be influenced by alertness or neurological considerations
• unilateral weakness may result in lowered gain, especially at lower frequencies
• primary use: extent of bilateral peripheral disorder
• helps to verify calorics
• if gain is quite low, then phase and asymmetry may not be measured
• confusion may arise when caloric irrigations and rotary chair may not agree

Question 12

asymmetry as a measure of rotary chair testing

Answer 12

• slow component velocity to the right compared with slow component velocity to the left
• gives indication of “bias” within the system
• this usually results from peripheral disorder that remains uncompensated
• cannot completely rule out central disorder
• remember this is yet another “piece of the puzzle”

Question 13

what are adult rotary chair techniques adapted for children

Answer 13

• rotary chair enclosure
• seated on parent’s lap
• tasking techniques
• is more of a screening than diagnostic
• more likely to be successful than with caloric irrigation, because this is fun and that is not

Question 14

active head rotation

Answer 14

• rotary chair does not require the pt to move his/her head, therefore it is considered a passive rotation
• there are systems available that offer active head rotation

Question 15

method of active head rotation

Answer 15

• may also be called the VAT test (vestibular autorotation test)
• pt wears lightweight helmet equipped with a sensor to measure head velocity
• instructions to the pt are for them to fixate on a target or vertical plane
• the speed of the head shake is matched to a computer generated tone

Question 16

VAT setup

Answer 16

• eye movements are recorded by electrodes or VNG goggles
• first 6 seconds are 0.5 Hz for calibration
• the remaining 12 seconds the freq changes gradually from 2-6Hz

Question 17

VAT measures

Answer 17

• Normal VAT responses:
• –gain values near 1.00
• —-peripheral vestibular lesions can produce abnormally low or high gains
• –phase values near 180 degrees
• –symmetrical right/left responses
• —-asymmetry associated with uncompensated unilateral vestibular lesions

Question 18

VAT and fixation

Answer 18

• because high head frequencies are tested, smooth pursuit contributes little to the response, and the test can be conducted in a lighted room while the pt fixates on a stationary target
• –can evaluate both the vertical and horizontal VOR

Question 19

why is VAT good for monitoring

Answer 19

• portable equipment that allows for bedside testing of hospitalized pts
• –test/retest reliability of the test: debated and it has not been adopted universally as a standard test of VOR function

Question 20

VAT disadvantages

Answer 20

• test/retest reliability and repeatability issues require vigilance from the examiner and cautious interpretation of test findings
• other somatosensory cues may contribute to results, so VOR may not be the only pathway involved
• the voluntary nature of active head rotation testing may allow pt to make predictive eye movements

Question 21

video head impulse test

Answer 21

*allows recording and computerized analysis of the head impulse or head thrust test used at the bedside (with head thrust you are looking for them to miss the target and have a catch-up saccade, this gives more info on the saccade

Question 22

what canals are tested with VHIT

Answer 22

• all 6 semicircular canals which gives greater info than the caloric test which examines only the horizontal canal
• lateral/LARP/RALP
• –examining the lateral canal is a back and forth horizontal motion and no concern of torsional eye movements interfering

Question 23

how do you turn the head when testing LARP

Answer 23

head turned 30 degrees to the right

Question 24

how do you turn the head when testing RALP

Answer 24

head turned 30 degrees to the left

Question 25

how to test VHIT

Answer 25

• turn head to the side 30-40 degrees but to the opposite side of what you would think (LARP turns to the right, RALP turns to the left)
• –this is to get the proper vertical eye movement without torsional interference
• –goggles are labeled so that the confusion is lessened
• once into position the head is dropped down 10 degrees and then raised 10 degrees rapidly
• the computer will analyse the head and eye velocities

Question 26

VHIT scores

Answer 26

• normal VHIT should reveal gain of greater than 70%
• if low values are found then a VOR weakness is suspected
• detection of covert corrective saccades (during head motion) and corrective overt saccades (post head motion) are a strong indicator of vestibular deficit