W3 Cochlear Implant Flashcards
Basics
Describe the origins of the CI (brief)
(year, where, comparison to now)
- University of Melbourne, 1978
- two out of three prototypes failed
- resulting company (Cochlear Limited) now has ~65% of world market with implants in excess of 350k people
What are the target neurons for sensorineural hearing loss treatment called?
Cochlear implants target the Spiral Ganglion Cells
- World population of hearing-impaired:
- Australian population of hearing-impaired:
- Approximately _% of the above that are profoundly deaf
- ___ M world-wide, __ k in Australia
- Approximately _% are severely hearing impaired
- _ M world-wide, __ k in Austrlia
- World population of hearing-impaired: ~120 M
- Australian population of hearing-impaired: ~1 M
- Approximately _% of the above that are profoundly deaf
- 2.4 M world-wide, 20 k in Australia
- Approximately _% are severely hearing impaired
- 6 M world-wide, 50 k in Austrlia
List the major milestones in the development of the bionic ear
(Hints: x5, 1790s Volta, 1950 - 1984 Nucleus)
- 1970s: A Volta shocks himself and hears explosion followed by thick soup boiling
- 1950s: Single channel cochlear implant devices in France and USA
- 1970s: 3M Corporation first commercially marketed (single channel) CI
- 1977: First successful multi-channel cochlear implant implanted in Vienna (later to become Med-EI)
- 1984: Nucleus multi-channel cohcelar implant (Melbourne research, Sydney manufacturing) approved by the US FDA
Today: more than 400,000 implanted
True or False:
Cochlear Implants use constant voltage pulses. Other devices (e.g. Medtronic deep brain stimulators) use constant current instead.
False
vice versa:
Cochlear Implants use constant current pulses. Other devices (e.g. Medtronic deep brain stimulators) use constant voltage instead.
Developers learn about spiral ganglion clel (SGC) survival by ‘playing’ with the inter-phase gap.
How is ‘charge per phase’ defined?
Charge = current (i) x time (t); in coulombs
(see image)
True or False?
Regarding the Stimulus Waveform:
Phase 1 starts the stimulation process. The onset of phase 2 has an influence on what happens next. The inter-phase gap controls this onset.
True
(see image)
Describe Phase 2 of the Stimulus Waveform
Charge recovery phase - typically of equal charge for maintenance of charge balance
List the following components of the CI (Nucleus CI24RE) in the attached image.
see image
Notes:
- stimulator - contains chip, which contains capacitors, transofrmer, etc. - hermetically sealed inside a titanium/ceramic chamber
- encapsulation is silicone, a polumer well-tolerated by body - structural, flexible, many good properties (leads also silicone)
- magnet - device is powered by inductors - bring two close together and current induced in the other. antenna - held into position by way of a magnet
Differentiate the modes of stimulation commonly used in modern cochlear implants.
Bipolar mode: current passed between a pair of electrodes both within the cochlea.
Common Ground mode: current passed between an intracochlear electrode and all the other intracochlear electrodes connected together. (goes through the tissue then returns to the electrode array)
Monopolar mode: current passed between one intracochlear electrode and one or more extracochlear electrodes.
Idea: should be able to stimulate from electrode to either the next (bipolar stimulation) or can skip one and stimulate further away (bipolar+1 / +2 / +3 etc.). Because the cochlea is tonotopically mapped (different regions respond to different frequencies), want to only narrowly stimulate certain neurons.
Compare Monopolar vs. Bipolar stimulation.
No perceptual difference really (?), but MP is most efficient (electrically), and BP most effective physiologically (slightly better efficacy/resolution of sound).
However, because the difference isn’t huge, it is rarely worried about such that the first implants sold did not have variable capabilities.
Monopolar is ‘perceived to go everywhere’ (stimulates everything), but with modern processing strategies this has been ‘reduced’ and is the most common way of stimulating now as this conserves battery power (99% of CIs; bipolar are far rarer).
Draw a shcematic of an Inductor-based Implant Power Supply (circuit diagram) (include external component before transmission across skin flap).
See image
(in Aus, circuit is tuned to 5 MHz)
See attached diagram of the anatomy of the cochlea. Which space does the electrode array of an implant situate?
Hair cells are inside the scala media. As these are lost in recipients of CIs, the targets are the spiral ganglion neurons. The most effective location for the electrode array is hence within the scala tympani.
List some competitors of Cochlear Implant technology
see image
