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Title: High power magnetic stimulation of the peripheral nervous system and the upper urinary tract
Author: Young, A. J.
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2007
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In theory many of the physiological effects of electrical stimulation should be repeatable with magnetic stimulation. The aim of this study was to investigate some of the potentially clinically relevant actions of high power magnetic stimulation on the mammalian peripheral nervous system. This investigation can be separated into 3 parts. Firstly, experiments examining the ability of 'wide pulse' electrical stimulation to produce complete reversible block of peripheral nerve were undertaken at both the compound and single unit level. The findings were used to estimate the magnitude of an impulse magnetic field required to produce 'magnetic nerve block'. Secondly, the design and construction of two prototype high power magnetic stimulators (HPMS) and their associated filed coils was carried out. Theoretical predictions and practical measurements of the output of each stimulator were undertaken. Thirdly physiological experiments with the HPMS's were performed, examining magnetic stimulation of unmyelinated nerve fibres in the upper renal tract. The aim of stimulating the kidney was to generate ureteric peristalsis, which may have a role in aiding stone excretion, especially post lithotripsy. For the electrical nerve block study the saphenous nerve in anaesthetized rats and rabbits was exposed. Either the whole nerve or fine filaments dissected from the cut proximal end of the nerve were studied. A-ap, A- 5 and C fibres were stimulated and blocked by wide electrical pulses with an exponential decay. The strength duration relationship of this response was studied and block was confirmed by failure of conduction of a proximally generated action potential to pass through the blocked region. Two HPMS's were designed and constructed in conjunction with Digitimer Ltd. and the department of Electrical and Electronic Engineering at Loughborough University. The first prototype was rated at 4.3 KJ and the second at 96KJ. Early on in structural testing it was found that conventional coil design was insufficient to allow repetitive shots, particularly with the 96KJ device. Redesign of the coil housing allowed multiple stimuli without failure. Finally physiological experiments with the prototype HPMS's demonstrated stimulation of C-fibres in the upper renal tract in a pig model. Magnetic stimulation of the kidney was able to generate ureteric peristalsis in the in-situ and exteriorized kidney preparations studied. Local anaesthetic applied topically to the renal pelvis and calyces blocked this response indicating that magnetic stimulation of ureteric peristalsis is a neurally mediated phenomenon. This thesis demonstrates that high power magnetic stimulation is technically feasible from both an engineering and physiological perspective. It can activate all classes of nerve fibre allowing the extracorporeal stimulation of internal organs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available