Wk8-Clinical Aspects- Internal components and speech processors Flashcards
CIs are perhaps the world’s most successful medical prostheses. What determine’s that?
< 0.2% of recipients reject it or do not use it
The failure rate needing re-implantation is around 0.5%
Describe the “Conceptualization” phase of CI development
1800-1949
- Volta’s “jumper cable” experiment
- Stevens et al identified 3 possible mechanisms underlying electric stimulation
When was the first reported confirmation of the effectiveness of CIs?
In 1977, during the “Research and Development” phase (1950-1979)
When was the “Commercialization” Phase?
1980-2008
Not all CI’s use a ground electrode (like monopolar). What are the 2 alternatives?
Neighbouring electrode (bipolar) or plate electrode
Though they differ in some ways based on manufacturer, what are 4 internal component similarities?
- all have an antenna
- all have a receiver/stimulator
- all have electrode arrays
- all have a magnet
What are the most important differences between different manufacturer CI’s?
- placement of reference electrodes
- pre-curved vs straight arrays
- removable vs non-removable magnet
- orientation of electrodes
- number of electrodes
- length of electrode array
One manufacturer offered 3 array options:
- a standard array for deep insertion
- a medium array for ____, ____, _____
- and a ____ array, which is 2 electrodes for significantly ossified cases
- a compressed array - shortened for Mondini or malformations
- medium array for fibrosis, re-implantation, or special cases
- split array
How is the split array inserted?
The longer array is implanted in the basal portion of the cochlea, and the shorter array is inserted through a second opening into a more apical location for cochleas that are severely ossified
CI arrays may vary by length, width, etc. What length might be considered for EAS?
24 mm or shorter
The Form24 has a tapered silicon portion at the base of the array. What is it’s function?
To prevent CS Fluid leakage
Why do we need so many lengths and types of electrodes?
- Cochleas come in many lengths
- most are 31 mm long, but vary from 25 m to 35 mm
- on a cochlear MRI, the distance b/w the oval window and most lateral point of the cochlea is measured. Size of distance and type of approach can help us estimate correct electrode array.
Why don’t we necessarily want as deep of a CI insertion as possible?
- Some research has indicated that deeper insertion (past the “hearing zone” of the spiral ganglion cells) may not improve ability to hear low frequencies, and may lead to worse outcomes
- deep insertion poses significant risk of cochlear damage
- > recommended higher density of electrode contacts within the hearing zone = greater flexibility
For a standard MRI, 1.5 tesla is enough, and most CI’s can withstand that with the magnet intact (and possibly a bandage to keep it in place). What happens with more detailed MRI’s, which may need 3 tesla?
The magnet must be removed during a day surgery the day before (only one manufacturer states a 3 tesla limit with the magnet in place (the Symphony))
How can we ensure that the electrode is inserted properly?
We can’t do an MRI b/c of the magnets, so we do an x-ray
- usually done right after surgery
- can do video x-ray during insertion, but not really needed.
