Rahal, Mouhamed Saleh; (2001) Optimisation of Nerve Cuff Electrode Recordings for Functional Electrical Stimulation Applications. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

There are about 600 spinal cord injuries (SCI) in Britain every year. The effects are irreversible and devastating, leaving parts of the body permanently paralysed. Functional Electrical Stimulation (FES) is a method to restore some partial functionality to paralysed muscles. Typical FES applications include restoration of hand grasp for tetraplegics patients, restoration of standing and standing up for paraplegics and restoration of bladder function for people with incontinence. Most of the early systems developed are open-loop systems with no feedback to regulate the stimulation. However, they are difficult to use because of their inability to cope with unexpected disturbances. Electroneurogram (ENG) activity recorded from peripheral nerves using cuff electrodes have been shown to be a reliable source of feedback in FES applications, eliminating most of the problems faced with externally-worn sensors. This thesis is dedicated to the optimisation of cuff electrodes in FES applications in terms of the suppression of EMG interference. The single fibre action potential is modelled using monopolar, bipolar and tripolar electrode structures using state of the art models. The effect of parameters such as cuff length, cuff radius, fibre diameter and electrode separation are investigated. It is found that in tripolar recordings the signal depends only on electrode separation and not on cuff lengths. The relationship between cuff geometry and interference from surrounding muscles in cuff electrode recordings is addressed. It is found that moving the end electrodes away from the cuff ends improves immunity from interference. A new cuff electrode configuration termed the screened tripole is proposed with higher inherent signal-to-interference ratio than current recording arrangements. Also in this thesis a closed-loop recording method is proposed, which allows the automatic nulling of residual Electromyogram (EMG) in tripolar electrode recordings. This method has the potential to reduce the high-order filters required in some FES applications. This will enable the development of mostly analogue systems, which are more suitable for implantation.

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