PRACTICAL USE AND CONTROL COMMANDS OF THE FES SYSTEM

Abstract

Functional Electrical Stimulation (FES) is one of the ways to restore motor functions of paralyzed extremities in stroke or cervical cord injury patients. By using our multi-channel FES system, some activities of daily living were restored in a paralyzed hand and arm. Howerer, in order to apply this system in clinical cases, selection of adequate control commands obtained from the patients' residual functions is essential for easy and sophisticated operations. This paper describes control strategy of EMG processing and its application to a C7 quadri-plegic patient for restoring his hand movements. Electromyograms (EMGs) during wrist movements were examined in five normal volunteers by bipolar intramuscular electrodes in order to select the wrist muscles for detecting control signals. It was found that the wrist movements were mainly differentiated by EMGs of the following muscles: extension by the extensor carpi radialis brevis (ECRB), abduction by the extensor carpi radialis longus (ECRL) and flexion by the flexor carpi ulnaris (FCU) or flexor carpi radialis (FCR). Therefore, EMGs of ECRB during wrist extension and FCR during wrist flexion were utilized as control signals for hand grasping and opening movements, respectively. Elimination of the stimulating pulses and evoked potentials (Mwave, etc.) from muscle discharges during active movements was performed by establishing a window of 16 msec for detecting muscle discharges preceding each stimulating pulse. From the clinical application of this system, it was found that grasping and releasing of the patient's hand were successfully achieved by EMG commands of the wrist muscles. Since the patient had utilized tenodesis for grasping light objects, the EMG commands detected from the wrist muscles provided easy and natural control of the hand movement. Thus, EMGs of the wrist muscles are suitable as a control command for FES. Further investigations on the processing of the EMG and the selection of muscles are necessary to develop a more sophisticated FES system.