Cerebral Blood Flow And Metabolism Measurement

At the present time several techniques are available for studying quantitatively global and regional blood flow and metabolism of the human brain. How ever, many scientists working in the clinical and research field who would like to use these tools for their investigations may be less familiar with the indi cations and limitations of the individual methods. The rapid development of both modern imaging techniques and new tracers may have led to some con fusion in answering the question as to which method is appropriate to solve the diagnostic problem of an individuum with brain disease. Scepticism and ignorance as to the methods to be used as tools in differential diagnosis of brain disorders may have prevented their widespread introduction into clinical practice. Thus, the significance of circulatory and metabolic parameters involved in the majority of diseases of the central nervous system may have been overlooked. The contributions compiled in this book describe in detail the individual techniques, outline their indications and limitations and deal in particular with newer methods such as the atraumatic 133Xe technique, stable xenon tomogra phy, three-dimensional techniques such as 133Xe single photon emission tomog raphy and N-isopropyl-P23-iodoamphetamine. Positron emission tomography studies provide information on function and metabolism, particularly that of oxygen and glucose, in regional brain areas of interest. Nuclear magnetic reso nance may be a promising method for studying metabolic parameters; however, accurate circulation measurements can not be performed at present.

This e-book will review special features of the cerebral circulation and how they contribute to the physiology of the brain. It describes structural and functional properties of the cerebral circulation that are unique to the brain, an organ with high metabolic demands and the need for tight water and ion homeostasis. Autoregulation is pronounced in the brain, with myogenic, metabolic and neurogenic mechanisms contributing to maintain relatively constant blood flow during both increases and decreases in pressure. In addition, unlike peripheral organs where the majority of vascular resistance resides in small arteries and arterioles, large extracranial and intracranial arteries contribute significantly to vascular resistance in the brain. The prominent role of large arteries in cerebrovascular resistance helps maintain blood flow and protect downstream vessels during changes in perfusion pressure. The cerebral endothelium is also unique in that its barrier properties are in some way more like epithelium than endothelium in the periphery. The cerebral endothelium, known as the blood-brain barrier, has specialized tight junctions that do not allow ions to pass freely and has very low hydraulic conductivity and transcellular transport. This special configuration modifies Starling's forces in the brain microcirculation such that ions retained in the vascular lumen oppose water movement due to hydrostatic pressure. Tight water regulation is necessary in the brain because it has limited capacity for expansion within the skull. Increased intracranial pressure due to vasogenic edema can cause severe neurologic complications and death.

Physiology of blood flow and metabolism -- Models of blood flow and metabolism -- Global control of blood flow -- Local control of perfusion -- Externally-based measurements -- Internally-based measurements -- Global changes in cerebral blood flow and metabolism -- Local changes in cerebral blood flow and metabolism -- Conclusions

An outgrowth of a 1987 teaching seminar at the U. of Glasgow, designed to update physiologists--particularly those in teaching positions--on the recent developments in the relation of cerebral blood flow to metabolism. The five papers might also be useful directly to graduate medical students. Distributed in the US by St. Martin's Press. Annotation copyrighted by Book News, Inc., Portland, OR

Until recently, monitoring of cerebral blood flow and metabolism was an unattained goal. Determination of cerebral blood flow was limited to intermittent measurements and particularly difficult to perform in critically ill patients. Meanwhile there are techniques available, however, to monitor cerebral blood flow and cerebral oxygenation, both globally and regionally. Therefore we thought it worthwhile to discuss these new continuous techniques and to compare them with well-known techniques which discontinuously measure CBF. For that purpose, an international workshop with some leading experts in the field was held in October 1992 in Berlin. The workshop consisted of about 20 lectures, either reviews on a special topic, or latest results. These contributions were given by invitation and were extensively discussed. Unfortunately it is impossible to reproduce the discussions. On the other hand, all speakers delivered a manuscript promptly after the meeting so that we were able to edit them within a short time. Since monitoring of cerebral blood flow in intensive care is a rapidly growing and changing topic, the written contributions should be quickly available. Authors, editors and publishers have tried to come close to this ideal. As editors we would like to thank the authors and the publishers who enabled us to come out with this volume of the proceedings as early as possible.

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