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Rotary Testing. Vestibular Autorotation & Rotary Chair Testing. THE BARANY CHAIR. ROBERT BARANY (1876-1936; Nobel Prize 1914) Invented device to stimulate the semicircular canals through controlled rotation. Passive and Active Rotation.

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rotary testing

Rotary Testing

Vestibular Autorotation

&

Rotary Chair Testing

the barany chair
THE BARANY CHAIR

ROBERT BARANY

(1876-1936; Nobel Prize 1914)

Invented device to stimulate the semicircular canals through controlled rotation.

passive and active rotation
Passive and Active Rotation
  • Passive– pt is moved (head or whole body) by examiner.
    • Halmagyi Head Thrust
    • Rotary Chair tests
    • Off-Axis Rotation
  • Active—pt is asked to turn their own head.
    • Head Shake
    • VAT
use of passive rotational testing
Use of Passive Rotational Testing
  • Verification of bilateral caloric weakness
  • Alternative when VNG/ENG calorics not possible
    • Pediatric population
    • External ear anomalies
  • Serial Monitoring
    • vestibulotoxicity
    • compensation
rotary chair tests
Rotary Chair Tests
  • Sinusoidal Harmonic Acceleration (SHA) Test:
    • Oscillating (left-right) in rotary chair
    • Freqs from 0.01 to 0.64 Hz
    • Peak angular velocities 50° per sec
  • Velocity Step Tests:
    • Sudden Acceleration to constant velocity (L or R)
    • Of 100° per sec2 for one second
    • Responses recorded:
      • Per Rotary (during rotation)
      • Post Rotary (following rotation)
    • Measuring Decay in slow phase velocity
expected responses in sha
Expected Responses in SHA

Eyes moving in opposite direction from head

  • Phase: Eye approximately 180° re: Head.
  • Magnitude: Eye speed < head speed
  • Symmetry: Right speed = Left speed
phase lead largest at lowest freqs
Phase Lead Largest at Lowest Freqs
  • below 0.16 Hz leads normally observed
  • leads increase from 0.04 to 0.01 Hz
  • Abnormally long leads: peripheral lesion
  • Abnormally short leads: cerebellar lesion
gain eye speed head speed
Gain (Eye Speed/Head Speed)
  • Gain generally higher at higher frequencies
    • reflects extent of peripheral weakness, bilaterally.
symmetry asymmetry
Symmetry/Asymmetry
  • Reflects vestibular system “bias”
  • Commonly, uncompensated Unilateral peripheral weakness
    • Produces stronger slow phase velocities toward weaker side.
  • But can reflect contralateral irritative lesion
velocity step
Velocity Step
  • Time Constant: time taken for eye velocity to decline to 37% of peak value
    • A measure of vestibular response decay (feature of the velocity storage mechanism).
  • Per rotary and Post rotary should be similar
  • Shepard criterion* : <13 second
    • Manufacturers provide norms
    • Variability: alerting, system noise.

*- Shepard (2001)

rotary chair testing
Rotary Chair Testing
  • Both Ears simultaneously
  • Helpful in Bilateral Caloric Weakness
  • Identifies different patients than VNG/ENG
    • 80% of symptomatic pts with normal ENG
    • Different frequency range than calorics
    • 66% sensitivity in pts with known lesions.
    • (compared to 90% with ENG)
vestibular autorotation test vat
Vestibular Autorotation Test (VAT)
  • “no” & “yes” gestures in time with metronome
  • Frequencies from 0.5 to 6 Hz over 18 seconds
  • While pt. fixates visually
  • Head motion recorded by accelerometer
  • Eye motion recorded via video or electrodes
vat normal responses
VAT Normal Responses
  • Gain values near 1.00
    • peripheral vestibular lesions can produce abnormally low or high gains.
  • Phase values near 180º
  • Symmetrical Right/Left Responses
    • asymmetry associated with uncompensated unilateral vestibular lesions.
head shaking test
Head Shaking Test
  • Pt shakes head for 20 seconds
  • With Frenzel lenses in dark room
  • Look for post-shaking nystagmus
dynamic visual acuity test
Dynamic Visual Acuity Test
  • Visual Acuity—discrimination of shapes of different sizes
  • during active head movement.
  • Packaged systems

/ Snellen Chart

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