Closed Loop Neuroprosthesis for Reach to Grasp Assistance: Combining Adaptive Multi channel Neuromuscular Stimulation with a Multi joint Arm Exoskeleton
Stroke patients with severe motor deficits cannot execute task oriented rehabilitation exercises with their affected upper extremity. Advanced rehabilitation technology may support them in performing such reach to grasp movements. The challenge is, however, to provide assistance as needed, while maintaining the participants' commitment during the exercises. In this feasibility study, we introduced a closed loop neuroprosthesis for reach to grasp assistance which combines adaptive multi channel neuromuscular stimulation with a multi joint arm exoskeleton. Eighteen severely affected chronic stroke patients were assisted by a gravity compensating, seven degree of freedom exoskeleton which was attached to the paretic arm for performing reach to grasp exercises resembling activities of daily living in a virtual environment. During the exercises, adaptive electrical stimulation was applied to seven different muscles of the upper extremity in a performance dependent way to enhance the task oriented movement trajectory. The stimulation intensity was individualized for each targeted muscle and remained subthreshold, i.e. induced no overt support. Closed loop neuromuscular stimulation could be well integrated into the exoskeleton based training, and increased the task related range of motion (p 0.0004) and movement velocity (p 0.015) while preserving accuracy. The highest relative stimulation intensity was required to facilitate the grasping function. The facilitated range of motion correlated with the upper extremity Fugl Meyer Assessment score of the patients (p 0.028) Combining adaptive multi channel neuromuscular stimulation with antigravity assistance amplifies the residual motor capabilities of severely affected stroke patients during rehabilitation exercises and may thus provide a customized training environment for patient tailored support while preserving the participants' engagement.
Front. Neurosci.