Electromyographic and Position Controlled Functional Electrical Stimulation of the Musculature about the Human Ankle Joint

Abstract

<p>In the last two decades, functional electrical stimulation (FES) has been investigated as a means for replacing lost function of limbs resulting from paralysis. Improvement in the gait of hemiplegic patients when gradually varying stimulation sequences were employed to control footdrop during the swing-phase of gait, led to the work presented in this thesis.</p> <p>The material described below is original to the field of FES.</p> <p>Two potential controllers of stimulus intensity and hence ankle joint position on the affected side have been explored. These are: the electromyographic (EMG) activity of the corresponding dorsiflexor and plantarflexor muscles on the contralateral side; and ankle-joint angle variations obtained from the contralateral side. The variance ratio, a statistical descriptor for repeatability, has been invoked to quantify the efficacy of EMG and joint position control. Practical time-constants of averaging have been determined for the processing of control and evoked EMG signals to be used in an FES-based orthosis incorporating feedback. Experiments have indicated that EMG, when used to modulate stimulus strength to effect control of ankle-joint position, is as efficacious as joint-angle-variation control. These experiments revealed that joint-position information is contained in the EMG records obtained from the prime movers during specific movements of the ankle joint.</p> <p>This thesis describes an initial attempt to control the affected ankle-joint position of hemiplegics during locomotion. Corresponding signals available from the contralateral side were used to modulate stimulus intensity on the affected side. A computer-controlled interactive program has been used to impose a delay proportional to the period of stepping between recording of the control signals and activation of the stimulators. Preliminary results obtained from a normal and a hemiplegic subject are presented, and their relevance to future thrusts in the field of FES are discussed.</p>