Browsing by Author "Hughes, Timothy John"

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    A blood-perfusion flowmeter
    (1975) Hughes, Timothy John
    A variety of methods have been used for measuring blood flow in large vessels. However, almost all of these methods are unsuitable for measuring perfusion flow in tissue. Basically all attempts at perfusion flow measurement have used either a tracer method (radio-active dyes, microspheres) or a thermal method where the rate of heat clearance from a heated probe is used as a measure of local flow. Tracer methods suffer from the fact that they give essentially a single measurement of flow and this only after tissue has been removed and analysed. Thermal methods on the other hand can give continuous measurement. What is actually being measured in the thermal method is the apparent thermal conductivity of the tissue in the immediate vicinity of the probe. The apparent thermal conductivity increases with flow as heat from the probe is not only conducted away by the surrounding tissue but is also carried away by the perfusing fluid. The way in which local perfusion is related to thermal conductivity and the methods used to measure thermal conductivity have led to criticisms of thermal methods. This work deals with instrumentation to eliminate some sources of error in thermal methods and automate the whole measurement procedure. It also includes a critical review of thermal methods in general and previous work in the field in particular.
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    Hot-thermistor spirometry for the artificial ventilation of infants
    (1982) Hughes, Timothy John
    This thesis describes equipment and techniques which were developed for use in monitoring mechanical aspects of artificial ventilation and optimising ventilation procedures. A strong emphasis is placed on the clinical applicability of the techniques and clinical applications are discussed. A new temperature-compensated hot-thermistor anemometer/spirometer was developed because the wide variety of spirometers described previously for-measuring respiratory volumes •and volume flow rates were unsatisfactory for routine use in monitoring infant ventilation. The principles of hot-thermistor spirometry were investigated both theoretically and experimental.ly to develop new temperature-compensation techniques and to predict the effect of gas composition changes on spirometer celebration. New electronic circuits were developed which greatly simplify the construction of temperature-compensated hot- thermistor anemometers and extend the dynamic range off low rates that can be measured.