Biomedical Engineering Reference
In-Depth Information
solution to the problem is to coat the whole electrode and leads with antibiotics.
Skin erosion occurs at the connector site. Low-profile connectors combined
with careful placement and closure should reduce the risk. Electrode or wire
break may occur when the head is moving or turning, which increases the stress
at the connector site. Electrode break requires another intracranial procedure
for replacement. Electrode migration is a very serious issue, since it leads to
clinical failure. Improvement of fixation techniques may solve this issue.
Furthermore, shocking sensations or intermittent stimulation may occur when
there is pacemaker dysfunction due, for example, to battery failure. Replacing
the battery means another surgical procedure to be performed on the patient,
albeit not intracranial.
Beside device malfunctioning, common adverse effects such as psychiatric
issues can occur including apathy, hallucinations, personality changes,
compulsive behavior, mania, depression, reduction of cognitive functions,
psychosis, and even suicide.
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All the complications with DBS electrodes reported recently in the scientific
literature have raised issues that must be addressed before this particular
industry segment can achieve complete commercial success. Medical reports
indicate that about a quarter of the patients implanted with DBS electrodes
have experienced hardware complications such as migration or dislodgement
of the leads. The authors tracked specific problems with the electrodes and
connectors, which included lead fractures, lead migrations, short/open circuits,
erosions, infections and foreign body reactions. Although they reported that up
to 70% of the Parkinson's patients experienced notable improvement resulting
from the procedure, it is clear that DBS could benefit from further development
of the hardware and surgical techniques.
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6.3 Motor Cortex Prostheses
Brain-controlled robotic limbs are still far from freeing paraplegics from their
wheelchairs or giving amputees their limbs back. These patients do retain the
mental dexterity to perform physical actions, even if the spinal cord is severed.
By accessing the region of the motor cortex responsible for a specific
movement, the intention to move can, in principle, be first decoded and then
translated into action with a prosthetic interface. Normally, millions of neurons
fire when an arm is lifted. However, the signal generated from only
approximately 100 neurons is enough to move a robotic arm at the shoulder,
elbow and even clench and open the hand. As a result, the robotic arm becomes
an extension of the body that would be easily controlled by thinking.
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In the particular case of the peripheral nerves employed for neuroprosthetic
applications, the detection and stimulation of their activity using electrodes
fabricated by microelectromechanical systems (MEMS) techniques have been
an important area of research in neuroengineering for over 25 years. Unlike the
electrodes implanted in the brain, which produce significant tissue damage at
insertion and later due to the motion of the head, leading to the deterioration of
the interface and a limited lifetime, the peripheral electrodes can be used for
