Cardiac Output And Regional Blood Flow

Although cardiac output is measured as the flow of blood from the left ventricle into the aorta, the system that controls cardiac output includes many other components besides the heart itself. The heart’s rate of output cannot exceed the rate of venous return to it, and therefore, the factors governing venous return are primarily responsible for control of output from the heart. Venous return is affected by its pressure gradient and resistance to flow throughout the vascular system. The pressure gradient for venous return is a function of several factors including the blood volume flowing through the system, the unstressed vascular volume of the circulatory system, its capacitance, mean systemic pressure, and right atrial pressure. Resistance to venous return is the sum of total vascular resistance from the aortic valve to the right atrium. The sympathetic nervous system and vasoactive circulating hormones affect short-term resistance, whereas local tissue blood flow autoregulatory mechanisms are the dominant determinants of long-term resistance to venous return. The strength of contraction of the heart responds to changes in atrial pressure driven by changes in venous return, with small changes in atrial pressure eliciting large changes in strength of contraction, as described by the Frank–Starling mechanism. In addition, the autonomic nervous system input to the heart alters myocardial pumping ability in response to cardiovascular challenges. The function of the cardiovascular system is strongly affected by the operation of the renal sodium excretion–body fluid volume–arterial pressure negative feedback system that maintains arterial blood pressure at a controlled value over long periods. The intent of this volume is to integrate the basic knowledge of these cardiovascular system components into an understanding of cardiac output regulation. Table of Contents: Introduction / Venous Return / Cardiac Function / Integrated Analysis of Cardiac Output Control / Analysis of Cardiac Output Regulation by Computer Simulation / Analysis of Cardiac Output Control in Response to Challenges / Conclusion / References / Author Biography

The effects of hypoxia on cardiac output and fractional distribution of regional blood flow were measured in unrestrained and unanesthetized Sprague-Dawley rats. Cardiac output was determined by thermodilution techniques, while blood distribution was determined by Rb86Cl and iodoantipyrine131 tracers. The animals were exposed 18-24 hours after cannulation to atmospheres of air and 7 and 10% oxygen in nitrogen. Cardiac output was higher in the hypoxic environments. Fractional distribution to brain, heart, and adrenal was increased, while that to the kidney and spleen was decreased in reduced O2 environments. (Author).

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.

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 4–5 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.

Cardiac output has always been a subject of interest to both clinicians and researchers in different branches of medicine and surgery. In the last decade more attention has also been paid to its application in pediatrics, neonatology, fetal medicine and pregnancy. Better understanding of the peripheral circulation has provided more insight into the patholophysiology of different diseases. Many cardiac and non-cardiac disorders affect cardiac outputs. Monitoring of the changes in cardiac output is also important in the acutely ill patient. There are several methods to measure cardiac output, each with advantages and pitfalls. This book deals with all relevant aspects of cardiac output in eight parts: part one describes the methods of measuring cardiac output and a comparison between the catheterisation based and the noninvasive techniques, while part two describes the changes in cardiac output due to physiological causes. Part three describes cardiac output in cardiac diseases and systemic hypertension. Cardiac output in acutely ill patients is discussed in part four. Effect of cardiac medications, temporary atrial pacing, permanent pacing, pharmacologic stress testing and anesthesia are covered in detail in part six, while changes in cardiac output in noncardiac diseases are described in part seven. Finally great attention has been paid in part eight to the regional circulation including cerebral, coronary, skeletal and splanchnic circulations. A separate chapter discusses in detail the dynamics of blood flow. This book will be useful both to the cardiologists as well as to physicians in other fields of surgery and medicine and to their trainees. Readers will find this book an interesting and a useful reference on the topic of cardiac output.

Reflex Control of the Circulation presents an interdisciplinary discussion of concepts in the reflex control of circulation. This volume describes aspects of autonomic receptor physiology, central pathways of reflex control, the electrophysiology of cardiovascular afferents, the interaction between reflexes, the autonomic control of regional blood flows, the autonomic control of fluid and electrolyte balance, and neurohumoral control of the circulation through normal and pathological states (e.g., hypertension, congestive heart failure). In addition, the regulation of regional blood flow during exercise and developmental aspects of reflex control are examined. Any researcher interested in the autonomic system and its role in circulation will find this book fascinating reading.

This unique book provides clinicians and administrators with a comprehensive understanding of perioperative hemodynamic monitoring and goal directed therapy, emphasizing practical guidance for implementation at the bedside. Successful hemodynamic monitoring and goal directed therapy require a wide range of skills. This book will enable readers to: • Detail the rationale for using perioperative hemodynamic monitoring systems and for applying goal directed therapy protocols at the bedside • Understand the physiological concepts underlying perioperative goal directed therapy for hemodynamic management • Evaluate hemodynamic monitoring systems in clinical practice • Learn about new techniques for achieving goal directed therapy • Apply goal directed therapy protocols in the perioperative environment (including emergency departments, operating rooms and intensive care units) • Demonstrate clinical utility of GDT and hemodynamic optimization using case presentations. Illustrated with diagrams and case examples, this is an important resource for anesthesiologists, emergency physicians, intensivists and pneumonologists as well as nurses and administrative officers.