Automatic Control of Standing Balance with FNS

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The purpose of this study is to provide meaningful standing function to individuals with motor complete thoracic spinal cord injuries via a new 16-channel implanted neuroprosthesis, and quantify its clinical and technical benefits over existing 8-channel implanted systems. Standing function will be achieved in the home and community environments through continuous supramaximal activation of the trunk, hip and knee extensors along with selected ankle plantar/dorsiflexors and hip ab/adductors in an open-loop manner. The additional channels of stimulation afforded by the new implanted stimulator-telemeter will improve several clinically relevant measures of standing performance over currently available systems. In addition, we will develop a novel control system to automatically regulate posture and actively restore standing balance to individuals in the well-controlled laboratory environment. Thus, we will begin to address the shortcomings of all other implanted functional neuromuscular stimulation (FNS) systems for standing by developing a sensor- driven control system that will actively monitor posture, anticipate perturbations to balance and automatically modulate stimulation to keep the user upright. This will be accomplished by combining innovative feed- forward, feedback and predictive control elements in three dimensions and at multiple joints based on global variables derived from a small number of simple, but information-rich, body-mounted sensors. Dynamic stability will be achieved by using accelerations of the trunk to predict and rapidly respond to the anticipated effects of perturbations, while static stability will be achieved by regulating center of pressure within the base of support using feedback control. A model-based approach to controller development will be adopted that involves computer simulation and laboratory testing with recipients of the 16-channel implanted stimulation system. The ability of the new control system to perform in the presence of spasms and changing muscle properties due to fatigue, as well as its sensitivity to control parameter selection and sensor accuracy, will be evaluated in simulation. This new control system should reduce reliance on the upper extremities while standing with FNS in the laboratory, thereby advancing the goal of eventually providing neuroprosthesis users with freer use of their hands to manipulate objects in the environment by automatically maintaining balance in the presence of intrinsic and extrinsic disturbances.