Continuous monitoring of blood flow.

An extensive review of the literature revealed that there are still significant weakness in the available technology for blood flow measurement. This dissertation describes two techniques for blood velocity measurement. The first is an invasive method which uses multimodal optical fibres for light transmission to and from a sensing tip, which attenuates the light depending upon the blood velocity. The design and construction of this flowmeter is presented and bench results shown. The modulated light is transmitted to the detection and processing circuit and provision is made for the transducer to be insensitive to pressure fluctuations and ambient light. The second technique, which is noninvasive, uses a continuous wave Doppler ultrasonic technique; the instrument designed is a portable directional Doppler velocimeter with purpose-built probes intended for monitoring blood flow in femorodistal bypass grafts in ambulatory patients. This portable unit differs from conventional Doppler units in many respect which are described. This unit has been developed in order to understand the behaviour of blood flow in grafts while the patients are persuing everyday tasks. A postoperative study of successful in situ vein grafts from 8 patients has been undertaken to determine the feasibility of the technique. This pilot study shows that posture can have an effect on blood flow in grafts, and also shows that it is possible to monitor blood velocity with Doppler techniques for a long period of time, without intervention of an operator.