Raised intracranial pressure and the cerebral circulation

Rowan, John O (1977) Raised intracranial pressure and the cerebral circulation. PhD thesis, University of Glasgow.

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Abstract

The first five chapters of the thesis review the literature on intracranial pressure, the cerebral circulation and their interrelation and set the scene for the experimental work which is described in chapters 6 to 11. Intracranial pressure is now measured routinely in many clinical centres but a great deal of caution is required in interpreting the results, particularly with respect to the method of measurement, the history of any raised pressure and the values of other physiological variables such as blood pressure and cerebral blood flow. The cerebral circulation itself displays a remarkable tendency to remain constant, the fundamental concept being that there exists a basic control mechanism which acts to maintain cerebral blood flow in order to meet the metabolic requirements of the brain. The methods used to measure cerebral blood flow in the work described are metabolically inert gas clearance techniques based on the Pick principle. Hemisphere blood flow in baboons was measured by the xenon-153 intracarotid injection technique while micro-regional blood flow was measured by the hydrogen clearance technique utilising inhalation of hydrogen gas. All pressures were measured by the use of in-dwelling fluid filled catheters and strain gauge pressure transducers. The effect of raised intracranial pressure on cerebral blood flow was examined in three animal models in which intracranial hypertension was created by different methods, viz:- general diffuse compression, focal supratentorial compression and focal infratentorial compression. These experiments confirm that the effect of raised intracranial pressure on the level of cerebral blood flow depends on the cause of the raised pressure. In each situation there are different effects on compensatory mechanisms such as blood pressure and cerebral resistance vessel diameter. The experiments on cerebrovascular pressures and resistances showed for the first time that intracranial pressure represents cerebral venous outflow pressure to within a few mmHg over a wide range of pressure values and also that outflow vascular resistance changes are independent of the cause of intracranial hypertension thus confirming that it is changes in prevenous cerebrovascular resistance which result in the different cerebral blood flow responses observed. The investigations into the blood pressure response observed during intracranial hypertension have demonstrated quite clearly that neither global cerebral ischaemia nor brain stem ischaemia is the trigger mechanism for the response. The results support the hypothesis that the initiating stimulus is local press\are changes both in the brain stem and spinal cord. Considerable doubt is also cast on the assumption that the role of the blood pressure response is to maintain cerebral blood flow in the face of rising intracranial pressure. Finally, it has been shown that an intact spinal cord is necessary for the maintenance of cerebral blood flow autoregulation to raised intracranial pressure, while autoregulation to blood pressure changes remains intact. This disassociation of the auto- regulatory function has not been previously demonstrated.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: J MA Lenihan
Keywords: Neurosciences
Date of Award: 1977
Depositing User: Enlighten Team
Unique ID: glathesis:1977-72085
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 13:04
Last Modified: 17 May 2019 13:04
URI: http://theses.gla.ac.uk/id/eprint/72085

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