The thesis reports an investigation of the mechanisms whereby the femoral artery supplying blood to a temporarily vasodilated skeletal muscle bed also dilates. Arterial diameter was continuously measured by an ultrasonic transit time technique, calibrated against distance by separate determination of the velocity of ultrasound in blood. An instrument capable of sampling up to four distances at repetition frequencies above 1 kHz was developed, and new methods of transmitter pulse triggering and received pulse amplification and detection are described. Design of optimal transducers for arterial, cardiac, venous and transcutaneous use is discussed in terms of testing by beam visualisation and other methods. The system runs for several hours without temperature drift and will resolve distance changes smaller than one micron. Trials by measurement of dynamic distension of a long water-filled rubber tube and comparison with manometrically measured phase velocity showed that the technique yields results within the range of predicted values from the various theories of pulsatile flow in rubber tubes. Blood pressure and flow and vessel diameter were measured from the exposed femoral arteries of anaesthetised greyhounds. Transient hyperaemia was induced by distal injection of vasodilator substances, nerve stimulation or occlusion of the femoral artery, and sustained high flowrate by establishing an arteriovenous shunt. Dilatation of up to 3% was observed in less than half of the experiments. The effects on the response of altering blood pressure, arterial constriction, and various degrees of arterial exposure and handling were observed. The data on exposure illuminate the controversy over the applicability to unexposed vessels of data obtained invasively. Locally originating response mechanisms were tested by perfusion of excised arteries at varying flowrates, pressures and pharmacologically induced tonic constriction levels. Conduction of constriction and relaxation was tested in vivo and in vitro by procedures to show the distant effects of locally applied pharmacological agents. Pressure and distension data were digitised and analysed by computer to determine wave velocities, elastic moduli and the importance of elastic non-linearity. Methods of finding phase, group and foot velocities were compared. The femoral dilatation response occurred after distal arterial section and when an arteriovenous shunt was established. Therefore the mechanism is not thought to involve conduction of dilatation commands from peripheral vessels. Temperature changes caused an opposite effect to high flow dilatation: the artery dilated slightly on cooling during occlusion and vice versa. The dilatation response is considered to depend on local sensing of increased arterial blood flowrate. Two such possible mechanisms are discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:449677 |
| Date | January 1975 |
| Creators | Bertram, C. D. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:509bc2f9-81d7-4303-beff-42c6fc67fd40 |
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