BMME 231 Presentation

1
Vestibular Prosthesis

• BMME 231 Presentation
• Punita Christopher
• 11/12/2004

2
The Balance System

• Five vestibular organs
• Situated in the inner ear within fluid filled
  bony labyrinth (perilymphatic fluid in
  perilymphatic space) and contain fluid filled
  compartments (endolymphatic fluid in
  endolymphatic space)
• Paired organs in contralateral ear - connected to
  each other in brainstem by vestibular nerve

(3)
3
Vestibular function

• Motion of subject ? displacement of the inertial
  element from rest position ? hair cells
  hyperpolarize or depolarize ? modulate the spike
  activity of the first order vestibular afferents
• Motion information travels on 8th nerve to
  vestibular nucleus
• Disease/injury can disrupt the peripheral
  three-link chain (inertial element, hair cells
  and nerve) of motion information
• A prosthesis would restore lost motion
  information

4
The need for a prosthesis

• The lack of sensory information results in
• Dizziness
• Blurred vision
• Inability to orient correctly (including the
  ability to align with the vertical)
• Reduced ability to stand or walk, especially
  under difficult conditions
• Serious consequences, such as increasing the risk
  of falling
• 6.2 million Americans report chronic problem with
  dizziness (2)
• Target groups that would benefit include (1)
• Bilateral vestibular hypofunction patients -
  those that dont get adequate motion cues from
  vision and proprioception during daily activities
• Causes include congenital abnormalities,
  hereditary/genetic degenerative diseases,
  exposure to ototoxic drugs (eg. Gentamicin),
  disease or injury
• Unilateral vestibular hypofunction patients -
  Imbalance in CNS
• Causes include disease or injury of the
  peripheral or central vestibular system (eg.
  viral vestibular neuritis or labyrinthitis,
  acoustic neuromas, chronic otitis media or
  mastoiditis, Menieres Disease, temporal bone
  trauma.
• Fluctuating vestibular function patients no
  adaptation
• early and middle stage MD patients, patients
  recovering from ablative surgery of the inner
  ear, and patients with viral attacks to the inner
  ear.
• Elderly population - prone to fall

5
Vestibular Prostheses

• Two approaches
• Provide head movement information to the nervous
  system directly by electrical stimulation of
  certain points in the neural pathways
• Provide the information via sensory substitution
  through other sensory systems (tactile, visual,
  auditory)
• Implantable
• semicircular vestibular prosthesis
• Non Implantable
• Stimulation of vestibular nerve through surface
  electrodes
• presenting self-motion cues via vibrotactile
  stimulation or electric currents applied to
  tongue/mastoid bone
• Vibrotactile displays successfully used by US
  navy to provide navigational cues to allow
  blindfolded people to control aircrafts (similar
  to postural control)

6
Basic Components and Design Issues

• Components
• Motion Detector - Linear accelerometers and
  rotation sensors fabricated using MEMS
  (micro-electrical-mechanical-systems)
• Application Specific Integrated Circuits -
  connects external devices to microprocessor
• Microprocessors
• Electrodes silicon microelectrodes
• Engineering Issues
• Miniaturization of sensors and electronics - lab
  device too large to implant (845 mm3)
• Misalignments and temperature sensitivity in
  micromechanical instruments
• Biocompatible materials and Sterilization
• Power consumption and transmission MEMS sensors
  require 150mW
• Biomedical Issues
• Implanted Nerve Stimulation
• Sensory coding of information to the CNS
• Site of stimulation effect of disease on site
  of stimulation, unilateral or bilateral modes of
  stimulation
• Surgical approach

7
Prototype Neural Semicircular Canal Prosthesis

• Goal implantable, vestibular neural prosthesis
  using electrical stimulation (1D rotational
  prosthesis)
• Angular velocity of head is measured
• Filtering to match the dynamic characteristics of
  the semicircular canals
• Digitally filtered signal is converted to
  stimulation frequency via a lookup table
• Charge-balanced pulses sent to nerves via
  platinum electrodes implanted near the nerve that
  is being stimulated
• Components contained in a box
• Tested in guinea pigs

8
Prosthesis Circuitry
(4)
9
Stimulation
(4)
10
Animal Experiments

• Experimental Setup
• Animal chair firm and painless restraining of
  animal
• Servo-controller rotation device used to rotate
  animal
• Animal in the center of search coil system
  (attached to rotation device)
• Head held stationary
• Angle adjusted so that horizontal canals aligned
  near earths horizontal
• Stimulation delivered to the nerve branch
  innervating the horizontal semicircular canal on
  one side
• Physiological Results Normal and Prosthesis
  animal
• Prosthesis animal adapted to baseline
  stimulation
• VOR (vestibular-ocular reflex) responses

(5)
11
Experimental Results and Conclusions

• During head movement, semicircular canals help
  stabilize the image of the external world on the
  retina
• When head moves left, VOR causes eye to turn to
  the right - Ability to do so lost in animal with
  plugged canals
• Prosthesis resulted in partial restoration of of
  animals eye movements (low gain)
• Better performance is necessary
• Performance not optimal at high frequencies
• Unilateral stimulation - Both lateral
  semicircular canals respond in a complementary
  manner
• Preliminary findings
• Electrical Stimulation can be used to provide
  motion cues in damaged vestibular system
• Animal responses adapt appropriately to chronic
  electrical stimulation
• Further Studies (6)
• Vestibular Adaptation
• Experiment on squirrel monkey
• Bilateral plugging of lateral canals

12
Non-Implantable Prostheses

• Galvanic Vestibular Stimulation GVS (7)
• Current delivered transcutaneously to the
  vestibular afferents through electrodes on
  mastoid
• Modulates the firing level of various afferents
  and depending on the current polarity causes the
  subject to lean back and forth
• Objective of study to test if the sway response
  brought about by GVS reduces the postural sway
• With GVS all subjects showed reduction in sway
  amplitude and latency

13
Vibrotactile Device

• Single axis research device provides subjects
  with a noninvasive, vibrotactile display of their
  body tilt
• All subjects sway significantly decreased when
  they were provided with vibrotactile display of
  their body tilt.
• Most subjects that fell without the device
  during the Sensory Organization Test
  (standardized clinical test of postural control)
  were able to stand without falling with the
  device turned on.
• Extended to a 3D system.

14
References

• Wall, C., 3rd, D. M. Merfeld, et al. (2002).
  "Vestibular prostheses the engineering and
  biomedical issues." J Vestib Res 12(2-3)
  95-113.
• Hoffman et al. (2000). Aging and chronic problems
  with balance and dizziness based on the
  1994/1995 disability supplement, American Journal
  of Epidemiology.
• Emedicine http//www.emedicine.com/
• W. Gong and D. M. Merfeld (2000). A prototype
  neural semicircular canal prosthesis using
  patterned electrical stimulation. Ann. Biomed.
  Eng., vol. 28, pp. 572581.
• W. Gong and D.M. Merfeld (2000), System design
  and performance of a unilateral horizontal
  semicircular canal prosthesis, IEEE Transactions
  on Biomedical Engineering 49 (2002), 175181.
• Lewis RF, Gong W, Ramsey M, Minor L, Boyle R, and
  Merfeld DM (2003). Vestibular Adaptation studied
  with a prosthetic semicircular canal, Journal of
  Vestibular Research 12 87-94
• Scinicariello AP, Eaton K, Inglis JT, and Collins
  JJ (2001). Enhancing Human Balance Control with
  Galvanic Vestibular stimulation. Biological
  Cybernetics 84 475-80
• Wall C 3rd, Weinberg MS (2003). Balance
  prostheses for postural control. IEEE Eng Med
  Biol Mag. 22(2) 84-90.