Final Rotary Chair,SHA,SV,Vfx,VVOR,AHR Flashcards
Slow phase is driven by what
Slow phase is driven by the ears (peripheral vestibular)
Fast phase is driven
Fast phase is driven by the CNS (central)
Nystagmus beats towards
Nystagmus beats towards the stimulated ear
Nystagmus beats away
Nystagmus beats away from an inhibited/affected ear
Describe the vestibular audiogram
Very Low F: Calorics
Low & Mids: Rotary Chair & hit
High F: Active head rotation
What are the two types of rotation tests?
Active & Passive
The patient move their own head
Active
Active Rotation Example
Vestibulo-autorotation test (VAT/Vorteq)
&
Headshake can be active or passive
Define Active RT
The patient move their own head
The patient is moved (head or whole body) by the examiner
Passive
Passive Rotation example
Halmagyi Head Thrust (HIT),
Rotary Chair Tests,
Off-axis rotations (SVV and SVH)
Define Passive RT
The patient is moved (head or whole body) by the examiner directly
Rotary Chair Evaluation Parameters
gain, symmetry & phase
Why is It unwise to test only one slow velocity
VOR functions at a wide range of velocities and to only test one and generalize would not be an accurate picture.
Pros of Rotary testing
Rotary testing is a more natural speed of head movement/ VOR function & more tolerable than calorics
Where is the axis of rotation?
The axis of rotation for rotary chair is centered between both labyrinths (bilateral stimulation)
CCW rotations
CCW rotations = left-beating nystagmus
- (left HSCC excitatory, right HSCC inhibitory effect)
- CCW is rotating to left
CCW - couterclock wise
CW rotations
CW rotations = right-beating nystagmus
* (right HSCC excitatory, left HSCC inhibitory effect)
* CW rotatess to the right
Rotatary Chair focus on what phase?
RC ONLY Focuses on Slow phases of nystagmus
* Fast phases are tossed out for analysis .
* All slow phases are then combined in a sinusoidal form for analysis.
Rotary chair can be used to examine the
Rotary chair can be used to examine the HSCC, central systems and vestibular nuclei.
Clinical application of rotary chair
- Evaluates bilateral vestibular loss (BVL); or patient w/ low calorics
- monitor for ototoxicity (vestibulo-toxicity)
- evaluate for CNS disorders
- Tells us degree of Central compensation
- guides Rehab therapy decisions
- evaluate vestibular function on those who can’t undergo caloric testing or w/ calorics that can’t be reliably compared
SHA stands for
Sinusoidal Harmonic Acceleration
SHA procedure
- velocity of 60 deg/s @ various freq
- Octave of .01-1.28
- 2-3 cycles for each freq
- start MF,HF then LF
- IN Darkness
- Must Task
SHA (VOR) Measurement Parameters:
Gain: eye movements relative to chair (head) movement
* Gain measured @ <.15 = no calc is made
Symmetry: difference b/w peak right beating and peak left bearing divided by sum of SPV (slow phase velocity)
* Most common in those with spontaneous nystagmus
Phase: compares timing of peak eye velocity to peak chair velocity
* most valuable, indirect measure of velocity storage mechanism
Spectral Purity: How clean the data is
* any artifact?
SHA
Normal or Abnormal?
Normal
Step Velocity examines what
The vestibular system’s central velocity storage
Step Velocity Procedure
- Patient is quickly accelerated to a constant velocity and rotated in one direction (CW or CCW) for about 1 minute
- Typically velocity used is either 60, 100 or 200 deg/s
- Velocities > 200 deg/s= more ear-specific
- stopped abruptly and post-rotary nystagmus observed for about 1 minute
- repeated for the opposite direction (CW or CCW)
- pre & post-rotary nystagmus are compared
Abnormal gain or duration patterns (called time constants) suggest specific deficits in the vestibular system
Step Velocity Test
- Performed in complete darkness with tasking
- Initial stimulation should show a burst of nystagmus beating toward the direction of rotation
- nystagmus will dispear over time as the subject maintains constant velocity
- stopped and their will be a second burst of nystagmus but in opposite direction
Both the gain and duration of the per-rotary and post-rotary nystagmus are measured
Summary
* Darkness - rotate = burst N - Nysta stops since rotation constant - Stopped = burt N but opposite
Step Velocity Measurement Parameters:
Gain = Initial peak gain SPV of nystagmus
* Measured pre & post-rotary
Reduced gain = Central, bilateral or unilateral vestibular disorders
* Greater rotational velocities (>200 deg/s) = more ear-specific (due to larger excitatory response)
Time Constant = Time required for nystagmus to decay to 37% of original peak gain SPV
* Measure pre & post-rotary
* Variable dependent on velocity of chair
* > 10 seconds = normal
shortened time constants = Central, bilateral or unilateral vestibular disorders
Step Velocity Reduced gain
Central, bilateral or unilateral vestibular disorders
Time required for nystagmus to decay to 37% of original peak gain SPV
Time Constant
Step Velocity
shortened time constants
shortened time constants = Central, bilateral or unilateral vestibular disorders
Normal time constant (sec)
Greater/equal to 10 seconds = normal
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.
Visual Suppression (Fixation) VFx:
Visual Suppression (Fixation) VFx
- fixate on point while being rotated in the chair sinusoidally. (visual is same speed as chair)
- Should be able to maintain focus on the light which will reduce the vestibular induced nystagmus.
- Failure to fixate = central sign (occipital, parietal lobe or flocculus of cerebellum)
- No tasking because there is a target
- Ensure good vision
VFx
Failure to fixate =
Failure to fixate = central sign (occipital, parietal lobe or flocculus of cerebellum)
Performed by projecting the OPK stimulus onto the wall of the rotary chair enclosure
Patient is rotated sinusoidally much like the VFx test but the OPK stimulus is stationary (does not move with the chair)
Visual Enhancement (VVOR):
Visual Enhancement (VVOR):
- Performed by projecting OPK stimulus on wall of rotary chair enclosure.
- patient is rotated sinusoidally and OPK stimulus does not move.
- Pursuit, OPK, and VOR systems contribute.
- Test is done if the patient has low gain for traditional SHA tests.
Rotational Chair Limitations:
- Tests VOR at low & mid frequencies
- Only shows Function of HSCC and SVN, + CNS & VN (no info about function of otoliths, IVN, or other SCC’s
- Can’t perform on claustrophobic or obese patients.
- poor ear specificity, will miss mild-moderate unilaterallosses
- lower cost, easy-to-use, more space efficent tool to measure the VOR during rapid head movements where visual stability might be impaired in a patient with a vestibular (VOR) deficit
- assess moderate to high frequency head movements not adequately addressed by rotary chair and provide a fuller representation of head movement and functional limitations experienced by patients at a substantially lower cost
Active Head Rotation Test (AHR)
Active Head Rotation (AHR) Procedure
- Goggles
- Metronome
- Patient would actively shake their head “yes” and “no” to the beat of a metronome over a specified frequency range
- Could also be performed with Dynamic Visual Acuity Test (DVA or DVAT)
Active Head Rotation Test (AHR)
- Used to measure VOR during rapid head movement where visual stability might be impaired in a patient with VOR deficit.
- assesses moderate - high frequency movements not assessed by rotary chair
- Cheaper
Active Head Rotation
measurement
Gain, phase parameters
AHR: compares & assess what?
- compares eye movements induced by active motion of the head
- assess mid to high frequencies. rotary chair is low - mid frequencies
AHR freq range
range 2 to 6 Hz
* Central oculomotor system can only move eyes at frequencies 1-2 Hz.
* To make sure you are assess peripheral it needs to be above 2 Hz
AHR limits
- goggles slip and can cause HF phase to be wrong
- Test-retest is insufficient
- Overestimate vestibular function because they have contributions from neck or higher cortical function
- No code to bill
