Research centering on blood flow in the heart continues to hold an important position, especially since a better understanding of the subject may help reduce the incidence of coronary arterial disease and heart attacks. This book summarizes recent advances in the field; it is the product of fruitful cooperation among international scientists who met in Japan in May, 1990 to discuss the regulation of coronary blood flow.
The aim of this treatise is to summarize the current understanding of the mechanisms for blood flow control to skeletal muscle under resting conditions, how perfusion is elevated (exercise hyperemia) to meet the increased demand for oxygen and other substrates during exercise, mechanisms underlying the beneficial effects of regular physical activity on cardiovascular health, the regulation of transcapillary fluid filtration and protein flux across the microvascular exchange vessels, and the role of changes in the skeletal muscle circulation in pathologic states. Skeletal muscle is unique among organs in that its blood flow can change over a remarkably large range. Compared to blood flow at rest, muscle blood flow can increase by more than 20-fold on average during intense exercise, while perfusion of certain individual white muscles or portions of those muscles can increase by as much as 80-fold. This is compared to maximal increases of 4- to 6-fold in the coronary circulation during exercise. These increases in muscle perfusion are required to meet the enormous demands for oxygen and nutrients by the active muscles. Because of its large mass and the fact that skeletal muscles receive 25% of the cardiac output at rest, sympathetically mediated vasoconstriction in vessels supplying this tissue allows central hemodynamic variables (e.g., blood pressure) to be spared during stresses such as hypovolemic shock. Sympathetic vasoconstriction in skeletal muscle in such pathologic conditions also effectively shunts blood flow away from muscles to tissues that are more sensitive to reductions in their blood supply that might otherwise occur. Again, because of its large mass and percentage of cardiac output directed to skeletal muscle, alterations in blood vessel structure and function with chronic disease (e.g., hypertension) contribute significantly to the pathology of such disorders. Alterations in skeletal muscle vascular resistance and/or in the exchange properties of this vascular bed also modify transcapillary fluid filtration and solute movement across the microvascular barrier to influence muscle function and contribute to disease pathology. Finally, it is clear that exercise training induces an adaptive transformation to a protected phenotype in the vasculature supplying skeletal muscle and other tissues to promote overall cardiovascular health. Table of Contents: Introduction / Anatomy of Skeletal Muscle and Its Vascular Supply / Regulation of Vascular Tone in Skeletal Muscle / Exercise Hyperemia and Regulation of Tissue Oxygenation During Muscular Activity / Microvascular Fluid and Solute Exchange in Skeletal Muscle / Skeletal Muscle Circulation in Aging and Disease States: Protective Effects of Exercise / References
The Social Security Administration (SSA) uses a screening tool called the Listing of Impairments to identify claimants who are so severely impaired that they cannot work at all and thus immediately qualify for benefits. In this report, the IOM makes several recommendations for improving SSA's capacity to determine disability benefits more quickly and efficiently using the Listings.
The fields of biological and medical physics and biomedical engineering are broad, multidisciplinary and dyanmic. They lie at the crossroads of frontier - search in physics, biology, chemistry, and medicine. The Biological & Me- cal Physics/Biomedical Engineering Series is intended to be comprehensive, covering a broad range of topics important to the study of the physical, che- cal and biological sciences. Its goal is to provide scientists and engineers with textbooks, monographs, and reference works to address the growing need for information. Books in the series emphasize established and emergent areas of science - cluding molecular, membrane, and mathematical biophysics; photosynthetic - ergy harvesting and conversion; information processing; physical principles of genetics; sensory communications; automata networks, neural networks, and cellular automata. Equally important will be coverage of applied aspects of b- logical and medical physics and biomedical engineering such as molecular el- tronic components and devices, biosensors, medicine, imaging, physical prin- ples of renewable energy production, advanced prostheses, and environmental control and engineering. Elias Greenbaum Oak Ridge, TN M. Zamir Department of Applied Mathematics University of Western Ontario London, Ontario, N6A 5B7 CANADA [email protected] Library of Congress Cataloging-in-Publication Data Zamir, M. (Mair) The physics of coronary blood flow / M. Zamir. p. cm. â (Biological and medical physics, biomedical engineering) Includes bibliographical references and index. 1. Coronary circulation. 2. Hemodynamics. 3. Blood flow. I. Title. II. Series. QP108.Z36 2005 612.1?7âdc22 2005042502 ISBN-10: 0-387-25297-5 e-ISBN: 0-387-26019-6 Printed on acid-free paper.
This presentation describes various aspects of the regulation of tissue oxygenation, including the roles of the circulatory system, respiratory system, and blood, the carrier of oxygen within these components of the cardiorespiratory system. The respiratory system takes oxygen from the atmosphere and transports it by diffusion from the air in the alveoli to the blood flowing through the pulmonary capillaries. The cardiovascular system then moves the oxygenated blood from the heart to the microcirculation of the various organs by convection, where oxygen is released from hemoglobin in the red blood cells and moves to the parenchymal cells of each tissue by diffusion. Oxygen that has diffused into cells is then utilized in the mitochondria to produce adenosine triphosphate (ATP), the energy currency of all cells. The mitochondria are able to produce ATP until the oxygen tension or PO2 on the cell surface falls to a critical level of about 4â5 mm Hg. Thus, in order to meet the energetic needs of cells, it is important to maintain a continuous supply of oxygen to the mitochondria at or above the critical PO2 . In order to accomplish this desired outcome, the cardiorespiratory system, including the blood, must be capable of regulation to ensure survival of all tissues under a wide range of circumstances. The purpose of this presentation is to provide basic information about the operation and regulation of the cardiovascular and respiratory systems, as well as the properties of the blood and parenchymal cells, so that a fundamental understanding of the regulation of tissue oxygenation is achieved.
Cardiologists must answer three important questions when evaluating and treating patients with a coronary artery stenosis. As a physiologist: "What is the effect of this stenosis on coronary blood flow and myocardial function?"; as a clinician: " Is this lesion responsible for the patient's symptoms?"; and finally as an interventionalist: "Will revascularization of this artery improve the patient?" Fundamentally, the answer to these questions can be given to a large extent by measuring coronary pressure. That is the rationale of writing this book. 1. 1 Historical overview. Andreas Gruentzig and most interventional cardiologists in the early days of PTCA, had the intuitive feeling that pressure measurements could help to establish the severity of a coronary stenosis and to monitor the progress and result of a coronary intervention. At that time, measuring coronary pressure by the balloon catheter was part of a standard procedure. A residual transstenotic gradient of less than 15 mmHg was generally considered as a good result. Later, however, it turned out that measuring these (resting) gradients with balloon catheters was inaccurate an only had a limited prognostic value. Moreover, because there was no consistent theory to correlate pressure measurements to blood flow, the interest in measuring coronary pressures faded and disappeared almost completely with the introduction of new balloon catheters not intended for pressure measurement.
The ultrasound velocity tomography allows measurement of cardiac geometries for various phases in the cardiac cycle. The present tomograph makes reconstruc tions at intervals of 20 ms. Because of a lack of clear (intramural) landmarks (except the roots of the papillairy muscle), it is difficult to pinpoint spatial trajectories of particular points in the heart. Therefore, a second method was developed of injecting radiopaque markers in the heart and following their motion patterns during the cardiac cycle with help of a biplane X-ray equipment. The data obtained with both methods can be implemented in our finite element model of the heart to compute intramural stresses and strains. The results obtained sofar with the extended Darcy equation to account for the interaction of blood rheology and tissue mechanics look promising. Further testing with more sophisticated subjects than mentioned in Figure 9 is required before it will be implemented in our finite element model of the heart. We conclude that analysis of regional cardiac function, including regional myocardial blood flow, requires still a major research effort but the results obtained sofar justify, to our opinion, a continuation in this direction. Acknowledgement The authors acknowledge Dr. C. Borst and coworkers for doing the animal experiments and prof. Van Campen and dr. Grootenboer for their participation is some aspects of this work.
