Abstract
One of the great unsolved problems of medicine and surgery is the cause of thrombosis in the veins of the leg. These thromboses occur postoperatively and may lead to swollen and ulcerated legs. A more serious and possibly fatal complication arises if part of the clot breaks off and gives rise to a pulmonary embolism. In view of the impressive advances that are being made in medicine and surgery, it is disquieting that the risk of dying from a pulmonary embolus is now twice as great as it was 20 years ago. Furthermore, recent work has shown that some 30% of all surgical patients develop thrombosis in the deep veins of the leg. This thesis presents a biomedical engineering approach to the problem. It has been suggested that one way in which the incidence of thrombosis might be reduced is to increase the venous return from the leg. This thesis is, therefore, concerned with the measurement and control of this flow. The thesis opens with a section on the measurement of vessel blood flow in which three techniques are considered in detail. First, electromagnetic flowmetry, which is used clinically in the later stages of the thesis, is investigated with particular reference to calibration errors. Secondly, the technique of local thermal dilution flowmetry is discussed and the design of the necessary instrumentation described in full. Thirdly, the possible application of light diffusion theory to blood flowmetry is analysed and tested using a simple flow probe. The section is completed by a short chapter on the design of an instrument for the measurement of vascular hydraulic conductance. The other main section of the thesis consists of an analysis of the effects of three parameters on venous flow in the leg. The three parameters considered are external magnetic fields, external pressure and rhythmic passive flexion. The thesis concludes with an appraisal of these techniques and outlines possible fields for future work.