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For decades, the monitoring of mixed venous oxygen saturation has been done invasively using fibre-optic catheters. This procedure is not without risk as complications may arise from catheterization. This thesis describes an alternative and novel means of monitoring venous oxygen saturation. The technique outlined involves inducing regular modulations of the venous blood volume and the associated measurement of those modulations using an optical sensor. Just as pulse oximetry utilizes the natural arterial pulse to perform spectral analysis of the peripheral blood in order to estimate the arterial blood oxygen saturation, the new venous oximetry technique uses the artificially generated pulse to perform the task of measuring peripheral venous oxygen saturation. This thesis explores and investigates the feasibility of this new venous oximetry technique. A heuristic model was first developed to predict the effects of introducing an artificially generated pulsatile signal in the venous system. The effect on the underlying natural arterial pulsation was also examined. Experiments were then conducted to justify and interpret the model developed. Other experiments were also conducted to optimize the design of the artificial pulse-based venous oximeter, to explore the effects of prolonged modulation of the venous system and to establish evidence that the measurements made were indeed related to venous oxygen saturation. It is concluded that the new venous oximetry technique is indeed feasible and with further research and development would one day replace the current invasive method.

Today's health professionals are facing a crisis in training needs: on one hand, the working hours of junior doctors and experience at the operating table are being reduced; on the other, patients are growing ever more critical and litigious. VR simulators may be able to provide a solution, but whilst hardware costs have fallen in recent years, they are still expensive when compared to conventional methods and few have been adopted. The challenge for researchers has been to create realistic, but affordable, surgical interfaces and to provide convincing assessments of the resulting systems. There are several common forms of assessment in the surgical simulation literature. The most popular would seem to be the construct validity test, in which experts' performance is contrasted with that of novices. Although this method provides a useful check, it is argued that the results are often unreliable, given the short-term nature of the test and the difficulty of separating practice and learning effects. Moreover, a wider literature search shows that consistency and persistency of performance are much more highly respected in eg. military and aviation contexts. A design for a virtual suturing simulator, dubbed FESTIVALS, is proposed which is based upon principles established in motor psychology over the last few decades. In particular, practice variability is promoted by requiring the user to employ both hands in facilitating access. Also, a delayed feedback schedule is introduced to provide feedback on errors. The Finite Element Method is adapted to build an accurate deformation model to support bimanual working and real-time haptic display. Evaluation of this system showed that the FESTIVALS system possessed good training and retention characteristics. In addition, a usability study collected feedback from clinicians which showed a generally favourable response and allowed several recommendations for future development. By considering discrete phases of the suturing data collected in these evaluations, it is also possible to show that construct validity held for several metrics. This is of particular interest because it appears to show that experts were much more capable of planning specific movements in advance, suggesting a more highly developed technique for error-control. This finding led to a novel proposal for an error-correction model of expertise.

This dissertation concerns the structural design of medical stent grafts. A new type of an innovative stent graft has been developed. Unlike the conventional stent grafts which consist of a wire mesh and a covering membrane, the proposed stent graft can be made from a single folded sheet of material. Firstly, a detailed symmetric design of a foldable cylindrical tube for the new stent graft has been presented. Folding is achieved by dividing the structure into a series of identical elements with hill and valley folds as in origami (Japanese art of paper folding). The folding patterns allow the stent graft to be folded and expanded both radially and longitudinally. The relationships among the design of the elements, the number of elements in the circumferential and longitudinal directions and the folded dimensions of the stent graft have been derived. It has been found that compact folding in the radial direction can be achieved by increasing the number of circumferential elements. A geometric mismatch during deployment has also been identified. The elements have to deform when the structure is expanded. Optimum designs which minimise the deformation have been found. Secondly, a new stent graft with helical folds has also been designed to improve radial strength and ease the deployment process. Helical folds are introduced by adjusting the joining position of the two edges of a sheet that had been symmetrically jointed in the symmetric design. The relationships among the number of elements in one complete circumference of a helix, the helical angle and the radius of the helical type stent graft have been established. The locations for the helical folds are optimised for easy folding by considering both geometric aspects of folding and the buckling patterns of a thin-walled tube under torsion, which are found analytically. Thirdly, using numerical analysis of the finite element method (FEM) the strain level and overall deformation of the stent graft during deployment has been calculated. Finally, the stent graft has been manufactured to verify the concept. A number of prototypes of the stent graft, which are the same size as standard oesophageal and aortal stent grafts, have been produced successfully using the same materials as current stent grafts of stainless steel and shape memory alloy (SMA) sheets. The patterns of folds on the materials are produced by photochemical etching. It has also been demonstrated that the SMA stent grafts self-expand smoothly and gradually by a near body temperature.