Setting up a paediatric balance laboratory

1
Setting up a paediatric balance laboratory

• Ewa Raglan
• GOSH and St Georges Hospitals, London
• PAIG/BSA meeting, Sheffield
• May 2009

2
Paediatric Vestibular Laboratory

• Why do we need it?
• Which patients should we refer for further
  testing to the vestibular laboratory?
• Dizziness/imbalance?
• Symptoms of vestibular dysfunction?
• Where/how many do we need?
• DH Good Practice Document on Paediatric
  Audiovestibular Services, Jan 2009
• Staff? Skills?
• Equipment?

3
Epidemiology Dizziness in paediatric population

• Underestimated, but less frequent than in adults
• Children with HL (30-70, Huygen 1993)
• Profound HL (30-40, Moller 2002)
• Age 1-15 (8 vertigo, Niemensivu et
  al 2006)
• Correlation between HI and vest function (Selz
  1996)
• Greater HL greater incidence of vest
  abnormalities ( Soundberg 1965)
• With increased prevalence of hearing imp. with
  age there is an increase of prevalence of vest.
  disorders
• (severe/profound 11000 neonates, 51000
  10-14yrs old) (Parving1996)

4
Reasons for vestibular assessment in HI child and
child with normal hearing

• Aids aetiological diagnosis
• (syndromes, metabolic dis, congenital structural
  anomalies, congenital infection)
• Helps genetic counselling
• Cochlear implantation
• Delayed motor development
• Recurrent unexplained falling
• Suspected malformation of the inner ear
• Ototoxicity
• Post meningitis
• Dizziness (migraine, MD, BPPV)

5
Clinical examination vs instrumental vestibular
testing

• Not every dizzy patient requires quantitative
  vestibular assessment
• Clinical exam. provides some qualitative
  information about vest. System
• The need to quantify vest. function for
  validation, establishment of prognosis, planning
  and evaluation of treatment
• Sometimes suspected vestibular abnormalities not
  shown by clinical evaluation may be shown by
  instrumental vestibular testing.
• There are no studies which would compare
  sensitivity and specificity of clinical
  vestibular examination to quantitative vestibular
  testing (caloric, rotation)
• No studies in children directly comparing
  clinical postural control tests with quantitative
  vestibular testing

6
Vestibular system maturation

• Anatomically developed functionally responsive
  by birth
• but, vestibular responses can be variable
• VOR normalise by 2mths of age, and mature further
  in first 2yrs of life
• OKN usually present at 3-6mths of age
• Smooth pursuit is normal by 5yrs old
• Majority of normal children demonstrate
  vestibular responses to caloric and rotational
  stimuli by 2mths old
• Lack of VOR response by 10mths is abnormal
• Technical modification of vestibular testing in
  children
• Broader range of normal in young children so the
  results should be compared with age-matched
  control subjects

7
Bedside vestibular examination

• To detect unilateral vestibular dysfunction
• Obs for SN
• (suppressed by visual fixation) but visible by
  fundoscopy or Frenzels glasses
• Head thrust
• (catch-up saccade with quick turns towards the
  unilateral loss)
• Head shaking nystagmus
• (N beats away from lesioned side), absent in
  normal subjects
• Vibration induced nystagmus
• (mastoid vibration -nyst beating away from the
  unilateral loss
• Dynamic visual acuity
• (3 line decrease in visual acuity during rapid
  head turns)- bil vestibular loss
• Hyperventilation
• accentuates the downbeating nystagmus in
  patients with cerebellar lesions

8
Bedside Examination

• Otolith dysfunction
• Skew deviation, head tilt
• Subjective visual vertical tilted 10-30 deg
  towards the site of lesion. May be present after
  vest. compensation took place
• Oculomotor testing
• Smooth pursuit tracking (of a moving target)
• Optokinetic response (OKN stimulus)
• Saccades testing (velocity accuracy, latency from
  one target to another)
• Dix-Hallpike test

9
Quantitative vestibular testing

• Recording eye movements
• to be able to reliably interpret the VOR response
• Help to localise neurological abnormalities
• EOG measures change in corneoretinal potential
  using electrode placed around the inner and outer
  canthi of the eyes allows recording of the
  direction, amplitude and velocity of eye
  movements
• VNG determines eye movements, using infrared
  cameras to detect eye movements in darkness
• Horizontal and vertical eye movements recorded by
  EOG
• Horizontal, vertical and torsional recorded by VNG

10
Vestibular Tests VOR
VOR - compensates for changes in head position
allowing images to be fixed on the retina when
head is moving
11
Diagnostic Tests of VOR
Caloric Test (low frequency)0.001Hz VAT
(active rotation) 2-6Hz Whole body
passive rot 0.05-0.6-1Hz
A
H
OVAR
Otolith
P
VAT active rot 2-6Hz
VEMP
12
Methods of vestibular stimulation

• Horizontal semi circular canal
• Caloric irrigation -equivalent to single very low
  frequency (0.003Hz)
• Rotational testing allows precise application of
  multiple frequencies of stimuli, but stimulates
  both ears simultaneously (active high frequency
  and passive low frequency)
• Stimuli for rotational testing
• Impulsive (rapid acceleration 100º/s/s to a
  constant speed)
• Sinusoidal (body side-to-side rotation)
• Measurement of VOR in rotational testing
• Gain SVC eye/head velocity
• Phase offset in timing of eye movement relative
  to head movement
• Asymmetry (in unilateral vestibular
  hypofunction)
• Caloric
• Interindividual variability of responses
  determines unilateral vestibular hypofunction

13
Rotational Testing

• Clinical use
• Presence of bilateral peripheral vestibular loss
• More specific than caloric testing for bilateral
  vestibular hypofunction
• Good correlation between low frequency VOR gain
  reduction, increase phase lead, reduced caloric
  responses
• Limitations
• Not sensitive in detection of chronic unilateral
  vestibular hypofunction

14
Modifications of Vestibular Testing Techniques in
Younger Children

• To improve calibration, ocular motor recordings
• Use flashlight, blinking toy for pursuit tracking
  in under 4 yrs
• Have a child look at the stars in gaze testing
  (Busis 1995)
• Make testing a game whenever possible
• Consider using a blindfold to help remove the
  effects of visual fixation in children who are
  unable to keep their eyes closed
• Converse with the child to keep him alert
• Use full field optokinetic stimulation

15
Modifications of Vestibular Testing Techniques in
Younger Children

• To reduce fearfulness
• Use warm water or air calorics of available
• Show an enlarged picture of a child wearing
  electrodes
• Allow parents to be present and to aid in testing
• Permit small children to sit in their parents
  lap
• Consider rotational testing is child becomes
  afraid of caloric
• To enable completion
• Test the most important element first and work as
  quickly and efficiently as possible eg if doing
  rotation, consider limiting testing to 0.01, 0.04
  0.16hz (Staller 1986)
• Shorten the duration of caloric irrigation

16
Consensus of Opinion (Fife et al 2000)

• Caloric (air, water) and rotational chair testing
  are considered established techniques for testing
  vestibular function in children
• In small children (3 yrs or below), rotational
  testing is more convenient
• In children 5yrs or over, either caloric or
  rotational testing can be performed
• Published studies raise no safety concerns in
  children undergoing caloric/rotational testing
• Children can be tested using any of the
  techniques used on adults with modifications
• There is more variability in the range of normal
  children

17
Bid for vestibular laboratoryBusiness Case

• Clinician Establish the need (geography, patient
  profile)
• Compare current situation with recommended
  protocols for services provided
• Specification for lab
• Capital/equipment committee (finance)
• Working party clinician, procurement, business
  manager, engineering dept, works (estates), ICT
  rep - involvement from the beginning
• Tender (invitation to tender to various
  companies)
• Choice of company (competitive)
• Contract, installation of the lab in a
  pre-prepared venue (floor, ceiling, ambient
  noise, supply of power, electricity, water)

18
Business case for the vestibular chair at GOSH-
BID

• The vest service an integral part of the
  comprehensive AM service crucial for diagnosis
  and management at the tertiary level
• Available specific vestibular expertise (medical)
• Recent developments in genetic hearing
  impairment, cochlear implantation, vestibular
  disorders in metabolic/neurological disease -
  need for the vest. service
• Delayed motor development in hearing impaired
  children and others, iatrogenic loss areas which
  would benefit from the ability to assess in
  detail both vestibular and balance systems (and
  help with rehabilitation)

19
Specification of vest lab for the tender process

• For children (birth 18yrs)
• Specification for HARDWARE
• Rotatory chair assembly to be able to carry
  weight of parent and child up to 250kg
• Chair-frame and headset with appropriate straps
  for parent child (waist, chest, legs)
• Chair seat size to accommodate parent and child
• Facility to fit a baby seat onto the frame for
  testing 0-1 year old
• cushion to be put on the chair for an older
  child to be able to sit independently
• Special mother/ child provision to allow the
  chair to be positioned up to 9 inches back from
  on axis to allow for testing of the child while
  in mothers arms, the slide mechanics should have
  a locking position
• System attached to the chair for assessing
  visual vertical for otolith testing
• OVAR (angle tilt from 0-30deg for otolith
  testing)
• Unilateral centrifuge for otolith testing

20
Specification of vest lab for the tender process
II

• OKN stimulus (spherical stimulus projector
  mounted to the ceiling)
• Pursuit tracking system - laser mechanics allow
  testing of horizontal/vertical axes, testing
  calibration, pursuit and saccades
• Caloric stimulus
• Eye movements recording system EOG and
  biological amplifier
• VNG
• Screen half circle facing chair for projection
  of stimuli
• Infrared camera mounted on the chair to
  visualise patient's face
• Infrared camera to visualise patient and the
  chair

21
Specification for software

• User friendly, allowing use of a range of tests
  to be able to make analysis of the response
  within short period of time, be able to operate
  the signal and provide analysis and present in
  graphical form eye movement or video oculographic
  recordings
• Flexibility of test protocols
• Analysis based on the best cycles of response
• A wide range of stimuli parameters available
• Means and SD of wide selection of normals should
  be used as reference tests
• Customised test summary
• Raw eye data to be saved and presented in a no.
  of graphs in relation to the stimulus
• The user should have the ability to withdraw data
  on particular patients from database
• Software should be stable with no interference
  if computer should crash

22
Tests enabled by the program detailed
specification

• Calibration
• Gaze testing
• Smooth pursuit
• Optokinetic
• Rotational Sinusoidal
• Rotational impulsive
• Saccades
• Safety features
• (emergency cut-out w/o excessive deceleration DC
  Tungsten lighting for reduced electrical
  interference, patient panic button)

23
Business case for clinical scientist

• Describe specific expertise
• (physics engineering computer knowledge)
• Demand (no. of patients tested/week)
• Potential income generation (figure)
• Sources of referrals (internal/external)
• Threats
• Strengths

24
(No Transcript)
25
(No Transcript)
26
Collecting meaningful information
Testing
27
ANALYSIS MODE
28
Analysis - Saccades
29
Analysis Smooth Pursuit
30
SHA, Test Parameters (Reference)

• In US testing typically at octave frequencies
• 0.01
• 0.02
• 0.04
• 0.08
• 0.16
• 0.32
• 0.64
• 1.28
• 2.0 Hz
• and same velocity
• Typically 60 deg/sec.

31
SHA, Test Parameters, Gain (Reference)

• Gain
• How much the eyes move compared to how much the
  chair rotates
• The eyes move opposite to the chair motion

32
SHA, Test Parameters (Reference)
33
SHA, Test Parameters, Gain (Reference)

• Test is considered abnormal if two consecutive
  test frequencies of rotation are abnormal
• Important to test all frequencies
• Mild reduction in low frequencies of rotation
  (lt.04 Hz) with normal high frequencies of
  rotation
• Uncompensated peripheral vestibular weakness

34
SHA, Test Parameters, Gain (Reference

• Abnormally low gain for or most rotational
  frequencies
• Bilateral peripheral end organ lesion (bilateral
  weakness)
• Should match your caloric results with some rare
  exceptions
• Abnormally high gain for all or most rotational
  frequencies
• Cerebellar lesions
• Should match ocular motor evaluation (they should
  show cerebellar abnormalities)
• Also seen in vestibular migraine, vestibular
  hydrops

35
SHA, Test Parameters, Phase (Reference

• PHASE
• Timing relationship between head/chair velocity
  and slow phase eye velocity
• In other words timing difference between the
  head/chair movement and the eyes response to
  that movement
• This timing difference is called the phase lag.

36
SHA, Phase (Reference)

• Increased Phase Lead
• In low rotation frequencies 0.04 Hz and less
• Suggests peripheral vestibular loss
  (uncompensated)
• But can also be vestibular nuclei
• In high frequencies of rotation gt0.04 Hz
• CNS
• Example Lateral Medullary Syndrome

37
SHA, Asymmetry (Reference)

• Compares the VOR slow phase eye velocity response
  to the chair rotation in one direction with those
  in the opposite direction
• Indicates the presence of an imbalance (bias) in
  the system.
• Bias usually happens from and uncompensated
  peripheral vestibular lesion
• Particularly if there is a phase lead in the low
  frequencies of rotation
• Bias can happen from an uncompensated central
  vestibular lesion
• Sensitive to patient attention

38
Normal Sinusoidal Harmonic Acceleration
39
Chair Rotation Sinusoidal Test

• Loaded Data Tab
• Raw Data

40
SHA, Compensated Unilateral Peripheral Vestibular
Lesion
41
Sinusoidal Harmonic Acceleration Compensated
Unilateral Peripheral Vestibular Lesion
42

• Bilateral Weakness (Horizontal Canal)
• Decreased Gain (abnormal grey area) for two or
  more frequencies
• If severe
• Phase will be unreliable
• Spectral purity may be unable to be in the normal
  range even with eyes wide open and perfect data
  capture

43
Sinusoidal Harmonic Acceleration Bilateral
Vestibular Weakness
44
Static Subjective Visual Vertical/ Horizontal

• In complete darkness orient a line vertical or
  horizontal
• Normal do this within about 1 degree
• So /- 2 standard deviations is /-2.5 degrees
• Abnormal patients point the line top to the bad
  utricle side.
• Need multiple repeat measures (6)

45
Static Subjective Visual Vertical / Horizontal
46
Static Subjective Visual Vertical / Horizontal

• Set the line consistently (mean with standard
  deviation, low variance)
• Recommend a minimum of 6 repetitions
• The top of the line will point to the weak
  otolith
• Right otolith weakness
• Line gt 2.5 degrees (more positive than 2.5
  degrees)
• Left otolith weakness
• Line gt -2.5 degrees (more negative than -2.5
  degrees)
• Bilateral otolith weakness
• Will not detect any different from normal if loss
  is symmetric
• The line will be straight up and down with in /-
  2.5 deg. or patient can be highly random
• Patients do show improvement over time --
  compensation

47
Business case for clinical scientist

• Describe specific expertise
• (physics engineering computer knowledge)
• Demand (no. of patients tested/week)
• Potential income generation (figure)
• Sources of referrals (internal/external)
• Threats
• Strengths

48
Labyrinth