American Society for Peripheral Nerve

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The First Permanent Human Implant of the Stimulus Router System: A Novel Blue Tooth Neural Prosthesis
Jaret Olson, MD, FRCSC; Michael J. Morhart; Liu Shi Gan; Einat Reid; Lisa Korus; Jan Kowalczewski; Arthur Prochazka
University of Alberta, Edmonton, AB, Canada

Neural prostheses (NPs) are electrical stimulators that help to restore sensory or motor functions lost as a result of neural damage. Currently existing motor NPs include surface and implanted systems. Surface NPs are technologically simple, noninvasive and relatively inexpensive. However, they often have inadequate selectivity, activating non-targeted muscles and cutaneous sensory nerves that can cause discomfort. We have developed a new type of NP, called the Stimulus Router System (SRS) (Gan et al., 2007, IEEE Trans Biomed Eng 54, 509-517). The system consists of implanted leads that “capture” some of the current flowing between a pair of surface electrodes and route it to a target nerve. The “pick-up” terminal of an SRS lead is implanted subcutaneously under one of the surface electrodes and the “delivery” terminal is secured on or near the target nerve. Previous acute and chronic animal studies have suggested that the SRS is safe and offers advantages that justify human trials.

Method: The SRS was implanted in a tetraplegic man with a C5/6 level spinal cord injury. Three SRS leads were implanted in his right forearm for activation of the finger extensors, finger flexors and thumb flexors for grasp and release. Prior to surgery, activation thresholds for finger extensors and flexors with pulsatile stimuli delivered via conventional surface electrodes were 7.5mA and 8.5mA respectively and sensory threshold was ~6mA. Maximal grip strength of 5 lbs was elicited at a surface current of 19 mA. At 10 days after surgery, the surface currents needed to activate the finger extensors and flexors via the SRS were 2.75 mA and 1.75 mA respectively. Maximal grip strength of 20 lbs was elicited at a surface current of 3 mA, about 50% of sensory threshold. The stimulation parameters fluctuated for the first 3 months but stabilized and remained below sensory thresholds thereafter. The implants remain functional at the time of this report, 11 months after implantation. The subject continues to use the system daily to perform activities of daily life, switching between grasp and release with a wireless earpiece that detects toothclicks (Prochazka, 2005, US Patent 6,961,623).

Results: The results show that the SRS can selectively and functionally activate human muscles without causing discomfort or pain. It can produce stronger muscle contractions at lower surface currents than conventional surface stimulation. We therefore believe it may form the basis of a new family of NPs.


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