The physiological mechanisms for achieving fecal continence and the results
of the surgical methods to correct incontinence are reviewed. The devices hitherto
designed to attempt to achieve continence artificially are discussed and an analysis of
4130 reported complications of a successful device for the control of urinary
incontinence (the AMS 800) are presented. Based on these reviews, the need to
design and evaluate a prosthetic anal sphincter is identified and such a device is
presented in this thesis.
The effect of circumferential occlusive pressure on the blood flow of porcine
colon was assessed by a Laser Doppler flow meter. It was demonstrated that distal
blood flow is reduced by 50% at 52 mmHg. The occlusion pressure required to
achieve continence to semi-solids was shown to be reduced by the introduction of
angulation both in a theoretical model and experimentally, using a specifically
designed fecal substitute.
The Neosphincter was, therefore, designed to simulate the normal physiology
of the anorectum by closing and angulating the bowel without causing crenation and
The design parameters of the device were evaluated in an in-vitro model and
its placement assessed in a series of acute animal experiments in a porcine model.
The effects of the prosthesis set at an operating occlusion pressure of 33-45 mmHg
were then evaluated in survival animal experiments by implantation in Yucatan minipigs
for up to 20 weeks. The device produced fecal continence in 85% of the
activation times without causing ischaemic injury. Mechanical complications
associated with the control pump were encountered and design faults were identified.
A new pump was designed by the author.
The effect of Neosphincter function on blood flow distribution in the human
colon was studied during colectomy using a prototype Laser Doppler flow scanner.
Blood flow remained greater than 50% at 60 mmHg occlusion pressure.
d flow remained greater than 50% at 60 mmHg occlusion pressure.
The data presented show that the Neosphincter achieves continence in the
mini-pig model and further suggest that continence would be achieved in the human
without producing intestinal ischaemia. Ethical approval has been obtained to
proceed to trials in human patients.