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Rotary Testing

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

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  1. Rotary Testing Vestibular Autorotation & Rotary Chair Testing

  2. THE BARANY CHAIR ROBERT BARANY (1876-1936; Nobel Prize 1914) Invented device to stimulate the semicircular canals through controlled rotation.

  3. 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

  4. 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

  5. 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

  6. Head & Eye Velocity Curves

  7. 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

  8. 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

  9. Gain (Eye Speed/Head Speed) • Gain generally higher at higher frequencies • reflects extent of peripheral weakness, bilaterally.

  10. 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

  11. 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)

  12. 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)

  13. 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

  14. Head and Eye Velocity in VAT

  15. VAT Gain and Phase Measures

  16. 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.

  17. Abnormal Phase & Amplitude

  18. A Patient with Vertical Oscillopsia O’Leary (2002)

  19. Head Shaking Test • Pt shakes head for 20 seconds • With Frenzel lenses in dark room • Look for post-shaking nystagmus

  20. Dynamic Visual Acuity Test • Visual Acuity—discrimination of shapes of different sizes • during active head movement. • Packaged systems / Snellen Chart

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