Rotary Chair Flashcards
What are the benefits for rotary chair?
More sensitive to bilateral vestibular loss, ototoxicity, and CNS disease than VNG
Easier to tolerate than calorics (good for those who cannot tolerate it)
Can be used to evaluate vestibular rehab potential
What are some limitations to rotary chair?
Only tells us about horizontal SCC function and SVN unless used with off-axis rotations for otoliths
You may not see mild vestibular losses
Was human rotation and centrifugation described long ago?
Yes, by aristotle
Five senses (wits) - sight, hearing, taste, smell, touch
Didn’t get a clear depiction of vertigo and rotation in text until the early 1900’s
There was no inclusion of the vestibular system in the senses
*In 1792 Charles Wells provided scientific evidence to suggest expanding Aristotle’s original 5 senses to include perception of motion by the vestibular system
What was the barany chair?
Invented by Robert Barany (Nobel prize 1914)
Hungarian physiologist
Invented a device to stimulate the semicircular canals through controlled rotation
The subject is placed in the chair, blindfolded, then spun about thevertical axiswhile keeping his head upright or tilted forward or to the side
The subject is then asked to perform tasks such as determine his direction of rotation while blindfolded, or rapidly change the orientation of his head, or attempt to point at a stationary object without blindfold after the chair is stopped
*still used by the military to some degree to demonstrate spatial disorientation effects
What was rotational testing originally used for?
Experimental medicine
Psychiatric disorders
Torture?
What are the expected responses for the rotary chair?
Eyes moving in opposite direction from head
Nystagmus beats toward a stimulate ear and away from an inhibited ear (keeping the VOR intact)
*should be about the same gain as the head movement
How do you measure rotary chair responses?
Phase: eye approximately 180 deg RE: head
Gain: Eye speed < Head speed
Symmetry: right speed = left speed
What is passive rotation?
The patient is moved (head or whole body) by the examiner directly
Examples: Halmagyi Head Thrust (HIT), Rotary Chair Tests, Off-axis rotations (SVV and SVH)
*more easy to control, but might not be able to move as fast as active
What is active rotation?
The patient is directed to move their own head
Examples: Vestibulo-autorotation test (VAT/Vorteq)
Headshake can be active or passive
*active is a little more realistic in their responses
Does the rotary chair expand our evaluation of the VOR to include more velocities?
Yes
Rotational testing is also a more ‘natural’ physiologic representation of head movement / VOR function and is typically more tolerable to patients than calorics
Is there bilateral stimulation for rotary chair?
Yes
CCW rotations = left-beating nystagmus
(left HSCC excitatory, right HSCC inhibitory effect)
CW rotations = right-beating nystagmus
(right HSCC excitatory, left HSCC inhibitory effect)
What phases are we concerned about for rotary chair?
Slow phases
Fast phases are tossed out by computer for analysis purposes
All slow phases are then combined in a sinusoidal form for analysis
Rotary chair can be used to examine the HSCC, central systems and vestibular nuclei
What are the clinical applications of rotational testing?
To evaluate for bilateral vestibular loss (BVL), or patient w/ low calorics
To monitor for ototoxicity (vestibulo-toxicity)
To evaluate for CNS disorders (vestibular nuclei, vestibulo-cerebellum, migraine, etc.)
To infer degree of central compensation to peripheral disorders and make determinations about rehabilitative therapy
To evaluate vestibular function on those who can’t undergo caloric testing or those w/ caloric responses that can’t be reliably compared (surgical ears, mastoid cavity, PE tubes, perforation, otorrhea, microtia/anotia, young children or handicapped
What is the typical test battery for rotary chair?
Calibration
Spontaneous Nystagmus (identifies any pre-existing nystagmus or other abnormality that may bias rotational responses)
Sinusoidal Harmonic Accelerations (SHA) - velocity of 50 or 60 deg/s; frequencies .01 – 1.28 Hz (possibly up to 2.0Hz; system dependent)
Step Velocities (60, 100, or > 200 deg/s)
Visual-Vestibular Interaction Tests (VFx (Visual Fixation / Suppression), VVOR (Visual Enhancement)
Subjective Visual Vertical (SVV) Tests (otolithic test of utricle)
What is velocity?
Speed
Distance/time
What is acceleration?
Change in speed (velocity) per unit of time
What is frequency?
Duration of movement
Acceleration + deceleration
What is the test battery for the sinusoidal harmonic acceleration test (SHA)?
Picks up where the caloric evaluation leaves off
Patient brought to velocity of 60 deg/s at various frequencies (typically octaves of 0.01-1.28 Hz)
Turned 180 degrees and then turns back
Minimum of 2-3 cycles recorded for each frequency
May use screening protocol of alternate octaves initially and fill in as needed
Typically begin with mid frequencies, highs, then lows (due to tolerance)
Performed in complete darkness
Must TASK the patient throughout
What are the SHA measurement parameters?
Gain - ratio of SPV of eyes to that of the chair/head (If measured gain is <.15 then no calculation of phase or symmetry will be made)
Symmetry - difference between peak RB and peak LB nystagmus divided by the total sum of SPV (most common in those with pre-existing spontaneous nystagmus or acute unilateral (uncompensated) losses)
Phase - timing component comparing timing of peak eye velocity to peak chair/head velocity (how long does it take the VOR to initiate)
Spectral purity - how clean is the data
What is abnormal gain for SHA?
Low gain across the board (typical for severe or complete BVL)
Reduced gain at low frequencies and normal in the highs is typical of mild or partial BVL (also seen in acute unilateral loss)
High gain responses don’t generally mean anything
What are some cautions with gain?
Ensure good calibration, patient alertness (meds/fatigue), complete darkness and appropriate tasking
How do you interpret symmetry data for SHA?
Ratio of right-beating nystagmus (SPV) should be approximately equal to left-beating nystagmus (SPV)
Asymmetric responses are common in those w/ pre-existing spontaneous nystagmus or acute (uncomp.) unilateral lesions
How do you interpret phase data for SHA?
For individuals who have phase leads (associated with peripheral vestibular loss)
Phase lags is generally central pathologies (often seen in those with cerebellar lesions or sometimes in those with migraine-related dizziness)
What is the step velocity test?
Also called the impulse acceleration test
Examines the vestibular system’s central velocity storage
Patient is quickly accelerated to a constant velocity and rotated in one direction (CW or CCW) for about 1 minute (typical velocities used are 60, 100, or 200 degrees per second)
Velocities at and greater than 200 degrees/sec are more ear specific
Patient is then stopped abruptly and post-rotary nystagmus observed for about 1 minute
Process repeated for the opposite direction (CW or CCW)
Initial nystagmus and post-rotary nystagmus are compared
How do you perform the step velocity test?
Performed in complete darkness with tasking
Initial stimulation should show a burst of nystagmus beating toward the direction of rotation
The nystagmus will dissipate over time as the subject maintains constant velocity
The chair is stopped and their will be a second burst of nystagmus this time in the opposite direction
Both the gain and duration of the per-rotary and post-rotary nystagmus are measured
What are the step velocity measurement parameters?
Gain - initial peak gain SPV of nystagmus (measured both during and after rotation); central, bilateral, or unilateral vestibular disorders can cause reduced gain
Time constant - how long it takes the nystagmus to decay to 37% of original peak gain SPV (measured both during rotation and after rotation); variable dependent upon velocity used (should use own norms); general rule is greater than or equal to 10 seconds is normal; central, bilateral, or unilateral vestibular disorders can cause shortened time constants
What is the criteria for interpretation of gain?
Variable dependent upon velocity (use own norms)
In General: Gain < 0.3 or >30% asymmetry (CW vs CCW) abnormal
Caution: Ensure good calibration, patient alertness (meds/fatigue), complete darkness and appropriate tasking
What is the criteria for interpretation for time constant?
Variable dependent upon velocity (use own norms)
In General: TC < 10 seconds abnormal (8-9 sec borderline)
Prolonged TC = non-localizing (possible migraine related)
Or for > 200 deg/s velocities, asymmetric TC = UVL on low side
What is the visual suppression test?
Patient is asked to fixate on a point of light projected in front of them on the enclosure wall while being rotated sinusoidally
Visual target travels at same speed as chair (travels with the patient)
The subject should be able to maintain focus on the light thereby significantly reducing or eliminating the vestibular induced nystagmus
Failure to fixate is a central sign
No need to task for this test
What is the visual enhancement test?
Performed the least
Performed by projecting the OPK stimulus onto the wall of the rotary chair enclosure
Patient is rotated sinusoidally much like the visual suppression test but the OPK stimulus is stationary (does not move with the chair)
Combo of contributions from pursuit, OPK and VOR systems
This test is usually done if the patient has low gain for traditional SHA tests (if the gain increases it implies an intact central vestibular system and the damage is peripheral) - patient would not be able to typically produce more nystagmus in this condition if the central system was damaged
What are some limitations to rotary chair?
Only tests VOR at low and mid frequencies (no highs) - 0.01 – 2.0 Hz for SHA (can be slightly higher)
Only tells us about function of HSCC and SVN (also central and vestibular nuclei)
Cannot be performed/evaluated on some patients (claustrophobic, obese)
Poor ear specificity (will miss mild-moderate unilateral losses as both labyrinths are stimulated the stronger (healthy) side drives the response)
What are active head rotation tests?
Created as a lower cost, easy-to-use, more space efficient tool to measure the VOR during rapid head movements where visual stability might be impaired in a patient with a vestibular (VOR) deficit
Idea was to better assess moderate to high frequency head movements not adequately addressed by rotary chair
Are active head rotation devices often incorporated with existing ENG/VNG equipment?
Yes, accelerometer clipped on to goggle and metronome
Patient would actively shake their head “yes” and “no” to the beat of a metronome over a specified frequency range (yaw and pitch plane)
Could also be performed with dynamic visual acuity test
*gain and phase parameters
What does active head rotation measure?
Compare eye movements induced by active motion of the head rather than passive head/body movements induced by a motorized chair
AHR devices assess mid to high frequency range whereas rotary chairs assess low to mid frequency range
(typical range - 2-6 Hz)
Need to be above 2 Hz to ensure that you are only testing the peripheral system (central oculomotor system can only move eyes at frequencies 1-2 Hz)
What are some issues with active head rotation clinically?
Goggle slippage on the head can cause high frequency phase to be incorrect / distorted
Test-Retest reliability is insufficient
VAT/VORTEQ tests, like all other “active” head rotation tests overestimate vestibular function because they have contributions from neck and/or higher cortical function
If you have a rotary chair, is there a need to do VAT/VORTEQ?
No
Information is largely redundant
Were people overusing the rotary chair code (92546)?
Yes, they were using it for active head rotation
Not permitted
No specific code for active head rotation tests
When can you bill the rotary chair code?
Bill one unit per plan of testing
Should only be billed with motor driven rotational chair
May also bill 92547 - use of vertical electrodes for recording purposes to reflect time to place recording electrodes not indicated with VNG
