Rotary Testing Vestibular Autorotation & Rotary Chair Testing

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

Passive and Active Rotation Passive– pt is moved (head or whole body) by examiner.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.Active—pt is asked to turn their own head. –Head Shake –VAT

Use of Passive Rotational Testing Verification of bilateral caloric weaknessVerification of bilateral caloric weakness Alternative when VNG/ENG calorics not possibleAlternative when VNG/ENG calorics not possible –Pediatric population –External ear anomalies Serial MonitoringSerial Monitoring –vestibulotoxicity –compensation

Rotary Chair Tests Sinusoidal Harmonic Acceleration (SHA) Test: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:Velocity Step Tests: –Sudden Acceleration to constant velocity (L or R) –Of 100° per sec 2 for one second –Responses recorded: Per Rotary (during rotation) Post Rotary (following rotation) –Measuring Decay in slow phase velocity

Head & Eye Velocity Curves

Expected Responses in SHA Phase: Eye approximately 180° re: Head.Phase: Eye approximately 180° re: Head. Magnitude: Eye speed < head speedMagnitude: Eye speed < head speed Symmetry: Right speed = Left speedSymmetry: Right speed = Left speed Eyes moving in opposite direction from head

Phase Lead Largest at Lowest Freqs below 0.16 Hz leads normally observedbelow 0.16 Hz leads normally observed leads increase from 0.04 to 0.01 Hzleads increase from 0.04 to 0.01 Hz Abnormally long leads: peripheral lesionAbnormally long leads: peripheral lesion Abnormally short leads: cerebellar lesionAbnormally short leads: cerebellar lesion

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

Symmetry/Asymmetry Reflects vestibular system “bias”Reflects vestibular system “bias” Commonly, uncompensated Unilateral peripheral weaknessCommonly, uncompensated Unilateral peripheral weakness –Produces stronger slow phase velocities toward weaker side. But can reflect contralateral irritative lesionBut can reflect contralateral irritative lesion

Velocity Step Time Constant: time taken for eye velocity to decline to 37% of peak valueTime 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 similarPer rotary and Post rotary should be similar Shepard criterion* : <13 secondShepard criterion* : <13 second –Manufacturers provide norms –Variability: alerting, system noise. *- Shepard (2001)

Rotary Chair Testing Both Ears simultaneouslyBoth Ears simultaneously Helpful in Bilateral Caloric WeaknessHelpful in Bilateral Caloric Weakness Identifies different patients than VNG/ENGIdentifies 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) “no” & “yes” gestures in time with metronome“no” & “yes” gestures in time with metronome Frequencies from 0.5 to 6 Hz over 18 secondsFrequencies from 0.5 to 6 Hz over 18 seconds While pt. fixates visuallyWhile pt. fixates visually Head motion recorded by accelerometerHead motion recorded by accelerometer Eye motion recorded via video or electrodesEye motion recorded via video or electrodes

Head and Eye Velocity in VAT

VAT Gain and Phase Measures

VAT Normal Responses Gain values near 1.00Gain values near 1.00 –peripheral vestibular lesions can produce abnormally low or high gains. Phase values near 180ºPhase values near 180º Symmetrical Right/Left ResponsesSymmetrical Right/Left Responses –asymmetry associated with uncompensated unilateral vestibular lesions.

Abnormal Phase & Amplitude

A Patient with Vertical Oscillopsia O’Leary (2002)

Head Shaking Test Pt shakes head for 20 secondsPt shakes head for 20 seconds With Frenzel lenses in dark roomWith Frenzel lenses in dark room Look for post-shaking nystagmusLook for post-shaking nystagmus

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