Tachtsidis, Ilias; (2005) Experimental measurements of cerebral haemodynamics and oxygenation and comparisons with a computational model: A near-infrared spectroscopy investigation. Doctoral thesis , UCL (University College London).

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Abstract

This thesis describes studies of cerebral oxygenation, autoregulation and metabolism carried out on human volunteers and patients. These studies are intended to aid both the development and the validation of a new physiology based mathematical model of the cerebral circulation and metabolism. The thesis contains comparisons between the experimentally derived data and predictions from this model. The experimental studies involve the measurement of systemic and cerebral haemodynamic parameters and their response to physiological challenges. In particular, near-infrared spectroscopy (NIRS) is used to monitor cerebral blood volume, oxygenation and flow. NIRS is a non-invasive technique, which uses the differing optical absorption of oxy-and deoxy-haemoglobin in the near infrared to monitor variations in oxygenation and blood volume deep within the tissue. A 2 channel NIRS instrument with spatially-resolved capabilities (NIRO 300, Hamamatsu Photonics KK), was used to monitor cerebral changes in response to physiological challenges such as hypercapnia, hypoxia and passive tilt in healthy volunteers. Furthermore we studied patients with primary autonomic failure with severe orthostatic hypotension undergoing a tilt test. The main reason for using data from these patients is that a comparatively minor physiological challenge (a 60 tilt) produces a major drop in arterial blood pressure and cerebral haemodynamics. The computational model, against which the experimental data is compared, is being developed at UCL. The model is capable of accepting experimentally determined data as an input and predicting changes in other measured and non-measured parameters. The thesis describes the model and illustrates its abilities using both theoretical and experimental data, in particular examining the measured and predicted changes in cerebral tissue oxygenation. Finally, practical aspects of clinical data monitoring are addressed and the capabilities and limitations of the cerebral modelling work are discussed. The findings and conclusions of these studies should be relevant to the wider mathematical, physiology and biomedical optics community.

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