The Use of Implanted Intramuscular FES system for Ameliorating Foot Drop During Locomotion
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Functional Electrical Stimulation (FES) is an assistive method for patients with dysfunctional nervous system who cannot functionally contract skeletal muscle to generate voluntary movement. By applying electrical stimulation on the skin, the muscle is able to generate the contractile force in which it previously wasn’t able to. Current FES systems rely on control systems that use external physical cues, such as a tilt sensor, to determine the timing of stimulation. This method still reflects some problems, as it doesn’t reflect individuality of patients and cannot function properly when the user walks on an inclined surface. This clinical research targets on examining the feasibility of developing an alternative control system that can control the muscle volitionally through the nervous signals generated by the user. A model of the FES system is created by stretching the gastrocnemius muscle and apply intramuscular stimulation in the decerebrated cat. It is hypothesized that the force of the muscle after electrical stimulation is higher than that without stimulation and this positive force feedback is only viable within a range of electrical stimulation. To test this hypothesis, a target tension of muscle contraction in an isolated feline muscle was used as the cue for electrical stimulation with the intent to boost that muscle contraction, that is, positive force feedback was used to initiate intramuscular stimulation as a means of increasing the force of muscle contraction in a decerebrate feline model. The maximum force and duration of contraction were compared when the muscle was stretched with and without stimulation. By varying the initial frequency of stimulation and the amount of stimulation relative to the force output of the muscle, the strength of distinct muscle contractions was increased. It is observed that below threshold values of these parameters no effect was observed and above threshold values tetanic contraction was initiated, but between the range of the intermediate values, the force of muscle contraction between the stimulated groups and the control group increased. These findings suggest that positive force feedback could be a potentially viable control system for FES systems.