Seattle Dizzy Group

Treating Chronic Vestibular & Hearing Loss with Cutting Edge Implanted Devices

by James Phillips, PhD

Director of the Dizziness & Balance Center at University of Washington Medical Center 

 (Presented to Seattle Dizzy Group on 11/10/18)

This presentation gives an overview of vestibular and auditory prostheses including how the University of Washington Medical Center is currently evaluating these cutting edge implanted devices which will hopefully help to improve the quality of life for many with chronic vestibular and hearing loss.

What is the Vestibular System?

• The vestibular system includes the structures in the inner ear that contribute to balance and orientation.
• It includes the nerves that relay balance and orientation information from the inner ear to the brain.
• It includes the neurons in the brain that make sense of that information, by combining information from a variety of sources:
  • different parts of each inner ear
  • from both ears
  • from the visual system
  • from the muscles and joints

What Parts of the Inner Ear are Parts of the Vestibular System?

• Semicircular canals
  • Posterior canal
  • Lateral canal
  • Anterior canal
    • Detect turning
• Otolith organs
  • Utricle
  • Saccule
    • Detect front-back, right-left, up-down
    • Detect tilt
• Vestibular Ganglia

What are the Semicircular Canals?

• 3 canals (posterior, lateral, anterior)
• Orthogonal
  • Fluid filled
• Ampula
  • Location of hair cells.  (Our sense of balance starts with hair cells!).
    • Like the hair cells in the cochlea for hearing
  • Neural transduction
    • Convert movement into neural signals

How Do the Semicircular Canals Work?

• When you turn your head fluid moves in the semicircular canals.
• Each ampula contains a cupula, which billows when the fluid moves, which in turn bends the hairs of the hair cells.
  • Gelatinous tongue
  • Embedded hair cells
  • Sense rotational acceleration

How Do the Otolith Organs Work?

• The otolith organs contain a gelatinous cap (otolithic membrane) and otoliths (otoconia, calcium carbonate crystals).  They also contain hair cells.
• When we slide or tilt, the gelatinous cap deforms, and the hairs of the hair cells bend.
  • Shear
  • Sense of tilt and linear acceleration

What Happens When the Inner Ear Vestibular System Fails Bilaterally?

Both ears fail to work:

• No whirling vertigo
• Significant Disorientation
  • Swimmy headed feeling
• Nausea and fatigue
  • Conflicting sensory input
• Anxiety
• Cognitive Impairment
• Oscillopsia
  • Failure to stabilize your eyes when you turn your head
  • The visual world moves when you move
  • Reduces your vision
• Postural and Gait Instability

Is There Compensation for Inner Ear Vestibular Loss?

• YES
• Over time we can compensate well for vestibular loss
  • Especially true of children
  • Our brains are designed to adjust for loss of input
• Compensation is dependent on learning:
  • not to misinterpret sensory cues from a non-working vestibular system
  • to use contextually appropriate cues
  • to develop a general strategy that is adaptive over a range of situations
  • to substitute useful information from other sensory systems:
    • Somatosensory System
    • Visual System
• Compensation requires sensory stability
  • Defeated by change of fluctuation

Can We Replace the Inner Ear Vestibular System?

Yes, with a vestibular prosthesis!

Who Could Be Treated with a Vestibular Prosthesis?

• Not patients with a single acute transient loss of function.
• Patients with bilateral loss of balance function.
  • Often iatrogenic
    • Exposure to ototoxic drugs
• Patients with uncompensated unilateral loss of balance function.
  • Large numbers of patients do not adapt to a loss from one ear
• Patients with fluctuating balance function.
  • Meniere’s Disease
    • Extreme intermittent vertigo
      • Destructive therapy
        • Injected ototoxin, surgical ablation, nerve section
        • These devices would take the place of a labyrinthectomy
• Usher Syndrome patients:
  • Bilateral loss of balance dysfunction
  • Combined with hearing loss
    • Usher Syndrome patients may already have inner ear implants (cochlear implants for hearing loss).
  • To effectively treat Usher Syndrome vestibular loss requires a combined vestibular and auditory implant.

UWMC Road to Human Trials

1. Design a device to stimulate vestibular afferent fibers.
   • Leverage a highly developed existing technology
     • Cochlear implant
   • Modify the software and hardware
     • Create a minimally invasive electrode technology
     • Create appropriate stimulation strategies
       • FM not AM
   • Partner with an existing Cochlear Implant manufacturer
2. Develop a simple surgical approach with the right target.
   • Three semicircular canals
     • Coherent rotational information
3. Construct prototype devices.
   • Identical to the final production device

UWMC Road to Clinical Trials

1.   Evaluate the device in animal model.
   • Implanted devices in 14 rhesus monkeys
     • Similar inner ear anatomy to humans
     • Test in intact and lesioned animals
       • Ideal model for unilateral and bilateral loss
     • Evaluate risk
       • Longitudinally evaluate inner ear function
         • Using identical clinical tests to those that are used diagnostically in humans
     • Evaluate efficacy
       • Longitudinally evaluate prosthetically elicited function
         • Using clinically relevant behavioral and physiological measures
2. Test the device in human patients with vestibular loss.
   • In 4 Meniere’s Disease patients
     • Can the device restore vestibular function lost from the destructive treatment?
3. Modify our devices to create a combined cochlear and vestibular prosthesis.
4. Test the new device in rhesus monkeys.
5. Modify our existing FDA IDE to test patients with hearing and vestibular loss with the new combined implant.
6. Test the new device in human patients with combined hearing and vestibular loss (2 additional patients, 6 total).

Turning the Implanted Device On

• Electrical stimulation with biphasic pulse trains
• Produces:
  • Eye movements – eVOR (Vestibulo-Ocular Reflex)
  • Body sway
  • Sensation of motion
• Effective vestibular stimulation does not produce:
  • Nausea
  • Pain
  • Sound sensation
  • Facial nerve activation

UWMC Research Team Conclusions

• We know that a vestibular implant works!
• We have tested such a device in animals and humans.
• We have an existing approval to test these devices in patients.
• We have built a combined vestibular and cochlear implant.
• We are currently testing it in monkeys.
• We are working with the FDA to modify our existing human trial to test this new device.
• We are not the only ones doing this!  (John Hopkins is researching similar implanted devices).

*This material regarding vestibular and auditory prosthetic technology is the intellectual property of the members of the device research team, the University of Washington, and Cochlear Ltd.*

More Information:

Conquering Vertigo article by James Phillips, PhD

James Phillips, PhD

Director of the Dizziness & Balance Center

University of Washington Medical Center