DEVELOPMENT OF A UNIVERSAL CONTROL UNIT FOR FUNCTIONAL ELECTRICAL STIMULATION (FES)1

Abstract

In collaboration with the College of Engineering the author has developed a laboratory, or clinic, based, battery operated "universal" control system, designed to improve disabled gait in upper motor neuron disabilities, especially stroke, hemiplegia, and cerebral palsy, by applying several channels of FES (Functional Electrical Stimulation) to the lower limb muscles while the patient is walking. The timing of the FES pulses, which can be applied to as many as six of the patient's muscles, is determined by potentiometer controlled one-shot timers, which are triggered by any of three switches in the sole of either shoe. Combinations of inverters, flip flops, AND gates and OR gates in the externally connected logic circuits determine the sequence of delays and pulses applied to the patient's muscles. This paper describes and diagrams some of the logic circuits and as an example of the possible application of the concept of a "universal" control unit reports the modifications of gait induced in a hemiplegic, four year post-stroke, patient. The characteristics of this patient's gait with FES in comparison to its characteristics without FES are demonstrated with motion picture frames, EMG recordings and graphic tracings of her right knee and ankle joint positions. They include more symmetrical timing of her right and left stance and swing phases, increased dorsiflexion of her right ankle in the swing phase, followed by a more distinct heel strike, and improved flexion--extension sequences of the knee and ankle joints and an increased heel rise in the stance phase. The author concludes that the gait characteristics of some hemiplegic patients will improve as they become adapted over a period of weeks or months to a control logic, which lessens their functional limitations by the use of a properly timed and amplified sequence of FES pulses. He suggests that the FES control requirements for individual patients should be determined experimentally with a control system "universally" adaptable to a wide range of disabilities, and that these control parameters could then determine the design of portable units, which may be used on a long term basis. These units would include only the operational options needed to duplicate the gait corrections found to be practicable for each individual patient, by the testing procedure, through a universal logic unit as described in this paper.