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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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