Closed-loop control of a FES system incorporating natural sensory feedback used for restoration of hand grasp in tetraplegics

A tetraplegic volunteer was implanted with an eight channel implantable stimulator to restore hand grasp function. He was also instrumented with a nerve cuff electrode around the cutaneous nerve innervating the radial aspect of the index finger. The nerve signal amplitude reflected mechanical events on the skin of the index finger. The activity from the natural sensors was used for automatic regulation of the stimulation intensities of the paralysed hand muscles. With the system in closed-loop control mode, the mean stimulation intensity to maintain a suitable lateral grasp could be significantly reduced compared to the stimulation intensity used by the subject in the open-loop control mode. We have shown the closed-loop FES system to function well on five separate days over a period of four months.