Current clinical testing of autoregulatory failure involves the patient undergoing a head-up tilt test. This is an experiment to investigate the sequence of physiological events that lead to a syncopal episode by tilting the patient from supine to 70% for up to an hour, or until the patient loses consciousness. This thesis argues that this test is no longer a suitable way of investigating these types of failures. An experiment was carried out to compare the effects of the tilt-test with a battery of other tests that have been used in the assessment of cerebrovascular autoregulation, namely carotid sinus massage, the transient hyperaemic response test, the Valsalva manoeuvre, and lower body negative pressure (LBNP). The first three tests were short, dynamic tests of autoregulation. The final test, and the tilt test, are longer, static tests. It was shown that lower body negative pressure produced more consistent results compared to the tilt-test, principally due to the stimulation of fewer systemic parameters by the test. The thesis also presents an experiment demonstrating for the first time measurement of blood flow to and from the brain during mild LBNP, using quantitative flow analysis conducted using magnetic resonance imaging. The results show a drop in cardiac output, which is reflected in a fall in blood flow in the carotid and vertebral arteries. The near-infrared spectroscopic data suggest that whist there was a drop in cerebral blood volume, sufficient perfusion was maintained through the test. This work provides a basis for future experiments, and the possibility of developing a more specific test to measure changes in blood concentrations locally in the cortex during LBNP.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:493983 |
| Date | January 2008 |
| Creators | Cherry, Patrick J. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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