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Rotary Testing - Rotary Testing Rotary Vestibular...

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Unformatted text preview: Rotary Testing Rotary Vestibular Autorotation & Rotary Chair Testing Rotary THE BARANY CHAIR THE ROBERT BARANY (1876-1936; Nobel Prize 1914) (1876-1936; Invented device to stimulate the semicircular canals through controlled rotation. Passive and Active Rotation Passive • Passive– pt is moved (head or whole body) by Passive– examiner. 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 • Verification of bilateral caloric weakness Verification • Alternative when VNG/ENG calorics not Alternative possible possible – Pediatric population – External ear anomalies • Serial Monitoring Serial – vestibulotoxicity – compensation Rotary Chair Tests Rotary • 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 Head & Eye Velocity Curves Head Expected Responses in SHA Expected Eyes moving in opposite direction from head • Phase: Eye approximately 180° re: Head. • Magnitude: Eye speed < head speed Magnitude: • Symmetry: Right speed = Left speed Phase Lead Largest at Lowest Freqs Phase • • • • 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 • Gain generally higher at Gain higher frequencies higher – reflects extent of peripheral weakness, bilaterally. Symmetry/Asymmetry Symmetry/Asymmetry • Reflects vestibular system Reflects “bias” “bias” • Commonly, uncompensated Commonly, Unilateral peripheral weakness weakness – Produces stronger slow phase velocities toward weaker side. • But can reflect contralateral But irritative lesion irritative Velocity Step • Time Constant: time taken for eye velocity to Time decline to 37% of peak value decline – A measure of vestibular response decay (feature of the velocity storage mechanism). • Per rotary and Post rotary should be similar Per • Shepard criterion* : <13 second – Manufacturers provide norms – Variability: alerting, system noise. *- Shepard (2001) Rotary Chair Testing Rotary • • • 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) Test • • • • • “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 Head and Eye Velocity in VAT Head VAT Gain and Phase Measures VAT VAT Normal Responses VAT • 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. Abnormal Phase & Amplitude Abnormal A Patient with Vertical Oscillopsia Patient O’Leary (2002) Head Shaking Test Head • Pt shakes head for 20 seconds • With Frenzel lenses in dark room • Look for post-shaking nystagmus Dynamic Visual Acuity Test Dynamic • Visual Acuity— discrimination of discrimination shapes of different sizes sizes • during active head during movement. movement. • Packaged systems / Snellen Chart Snellen ...
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