PhD Project: Neutralisation of myoelectric interference from recorded nerve signals using models of the electrode impedance

Supervisors: Dr. Andreas Demosthenous and Prof. Nick Donaldson

Any form of paralysis due to spinal cord injury or other medical condition, can have a significant impact on the quality and life expectancy of an individual. Advances in medicine and surgery have offered solutions that can improve the condition of a patient, however, most of the times an individual’s life does not dramatically improve. Implanted neuroprosthetic devices can partially restore the lost functionalities by means of functional electrical stimulation techniques. This involves applying patterns of electrical current pulses to innervate the neural pathways between the brain and the affected muscles/organs, while recording of neural information from peripheral nerves can be used as feedback to improve performance.

Recording naturally occurring nerve signals via implanted electrodes attached to tripolar amplifier configurations is an approach that has been successfully used for obtaining desired information in non-acute preparations since the mid-70s. The neural signal (i.e. ENG), which can be exploited as feedback to another system (e.g. a  stimulator), or simply extracted for further processing, is then intrinsically more reliable in comparison to signals obtained by artificial sensors. Sadly, neural recording of this type can be greatly affected by myoeletric (i.e. EMG) interference, which is present at the neural interface and registered by the recording amplifier. Although current amplifier configurations reduce myoelectric interference this is suboptimal and therefore there is room for improvement. The main difficulty exists in the frequency-dependence of the electrode-tissue interface impedance which is complex.

In the very specific case of a bladder control implant, we want to record signals from appropriate neural pathways that would help us determine whether or not the bladder contracts and act accordingly, i.e., neuromodulate to suppress the contractions and prevent incontinence. The amplifier has to detect changes in neural signal that are very small (i.e. sub-microvolt) with interference sharing part of the spectrum and having about 3 orders higher magnitude than the neural signal. Also, as this approach
is meant to be used by a person with permanent disability, it has to be performed 24 h per day and for that reason a rechargeable battery must be used to provide power to the implant. Therefore, the aim of this project is to come up with a new amplifier configuration that would offer very good interference neutralisation in the ENG bandwidth and be power efficient. Researchers are hoping that by combining neuromodulation for reflex incontinence with neurostimulation for bladder emptying, the bladder could be completely controlled without having to cut any of the sacral sensory nerves.

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