A self-optimising portable FES system using an electrode array and movement sensors

A portable functional electrical stimulation system has been designed using embedded systems technology. The system, which was applied to patients suffering from foot drop, uses sensors to monitor foot movement and orientation in a unique way, uses sophisticated algorithms for feedback, and drives an array of surface electrodes for stimulation. This system meets British Standards and safety requirements for medical equipment. A new technique was invented based on using the twitch response of muscles to optimise the configuration of the electrode array. This reduces the setup time in the clinic. Using feedback from the sensors, the optimum configuration of electrodes is chosen to produce correct stimulation and movement in real time. The instrument presents the patient with a ranked list of electrode combinations that are likely to be optimum; the patient can then choose a combination that is both effective and comfortable. The system is also able to vary the chosen pattern of electrodes and the stimulation signal parameters during the stimulation process. This may enable some problems associated with fatigue and skin irritation to be reduced. Trials were carried on 30 controls and 12 patients to test the instrument and study and develop the system optimisation and control algorithms. These preliminary clinical trials showed that control of the stimulation during walking, based on the optimisation algorithms developed in this work, gives high quality correction of foot drop. This was shown by gait assessment analysis by the physiotherapists involved in the project and blind assessment using independent researchers. These trials prove that the concept of using the electrode array for stimulation has advantages over using a conventional 2-electrode system.