Feedback control of standing balance using functional neuromuscular stimulation following spinal cord injury.

摘要

Functional neuromuscular stimulation (FNS) has been used to restore basic standing capabilities to individuals with spinal cord injury (SCI). In current clinical practice, constant open-loop stimulation is applied to continuously activate extensor musculature and maintain erect standing. This leaves the user to stabilize against postural disturbances by using their arms to apply support loading on an assistive device or surface. The ability to reach and manipulate objects while maintaining standing posture with minimal effort is consequently compromised. The next major advancement in improving FNS standing function is employing feedback control to modulate stimulation levels and produce automatic postural corrections to balance against disturbances and facilitate ease of use. Previous investigations in closed-loop FNS standing have examined controlling individual joints along single planes of movement and demonstrated measurable improvements in disturbance rejection. However, optimal clinical standing function requires unconstrained, three-dimensional (3-D) movements actuated synergistically by multi-articulate musculature. This dissertation project investigates the potential of using feedback to control stimulation levels to paralyzed musculature spanning the ankles, knees, hips, and trunk for control of standing in 3-D against postural perturbations. Initially, model-based methods were developed to create control systems employing feedback of joint kinematics and total body center of mass (COM) acceleration. These systems were subsequently evaluated for performance, robustness to feedback error, and quantity of sensor-based feedback potentially required. Simulation results indicated that a significant reduction in user upper extremity (UE) loading against postural perturbations is feasible with feedback control compared to the clinical analog of constant, maximal muscle excitation. For laboratory evaluation, a control system utilizing COM acceleration feedback was created for a specific user of an FNS standing system with 16 channels of intramuscular stimulation. Compared to the baseline case of constant stimulation levels used clinically, feedback control reduced the mean UE loading applied by the user by 33% against external perturbations and by 27% during volitional reaching activity. Future work should consider applying these feedback control methods to additional participants with novel stimulation paradigms, creating validated user-specific model control systems, developing algorithms to quickly adapt controller parameters according to time-varying stimulated muscle output, and selectively incorporating joint feedback.