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Young DB. Control of Cardiac Output. San Rafael (CA): Morgan & Claypool Life Sciences; 2010.

Cover of Control of Cardiac Output

Control of Cardiac Output.

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Preface

We learn early in our education that blood is pumped by the heart through the arteries, first to the lungs and then to the rest of the body, returning to the heart through the veins. However, the circulation that now seems so obvious was not understood until the eighteenth century when Hale first described it. He recognized that the heart was the center of the circuit, providing the motive force propelling blood at high pressure into the arteries. For the next several hundred years, physicians and physiologists inferred from the heart’s power and position at the center of the system that it controlled the flow of blood throughout the body, and today, the majority of physicians still may believe cardiac output to be regulated by the pumping strength of the heart. However, during the 1950s, Arthur Guyton and coworkers conducted an extensive series of experiments that, together with what had been learned earlier by Starling, Wiggers, and many others, led to the conclusion that, in fact, the normal heart could do little more than pump what returned to it from the veins; it had no control over the rate of output but could only respond to the flow of blood into its chambers. Guyton concluded that cardiac output was controlled instead by the factors that regulated the flow of blood from the body back to the heart. While this may seem to be a straightforward hypothesis, the circulatory mechanisms involved in mediating the control are complex and interrelated with other systems, and consequently, the full understanding of cardiac output regulation requires command of many aspects of physiology.

The publications of Guyton and coworkers and their contemporaries beginning approximately 50 years ago essentially provided all the data required to strongly support this hypothesis, and their conclusions were formalized in 1973 in the second edition of Circulatory Physiology: Cardiac Output and Its Regulation by Guyton et al. [1]. My purpose in this publication is to reacquaint the reader with the concepts they had developed, concentrating less on the techniques and data from the original experiments and more on the resulting concepts. In addition, more recent significant elaborations and modifications of the original work are included, along with results of simulations designed to assist in appreciating the work. I consider this to be worthwhile because a full presentation of the concepts is no longer available, and to this day, they are valid and essential in understanding circulatory physiology and pathology.

The concepts developed over the past 50 years are the basis of a complex mathematical model, Digital Human, developed by Thomas G. Coleman, a coauthor of the aforementioned book. The equations that comprise the cardiovascular section of the model were derived directly from the concepts and logic developed earlier by Guyton, Coleman and associates, and therefore, its simulations are faithful representations of the theories of operation of the cardiovascular control system based on that logic. I encourage the reader to take advantage of Professor Coleman’s outstanding work and use Digital Human to investigate additional aspects of cardiovascular control (go to http://digitalhuman.org.).

Physiologists and clinicians learned many things from Arthur Guyton; among the most important may be that worthwhile understanding of physiology requires the study of more than tissues or organs, but instead analysis of complete systems, with time as a variable. The lesson is well illustrated by the concepts he developed concerning cardiac output regulation.

Copyright © 2010 by Morgan & Claypool Life Sciences.
Bookshelf ID: NBK54471

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