Physiology of the Heart [antikvár]

Preface Why write a textbook about the biophysical basis of cardiac function? Of what importance are the energetics and chemistry of myocardial contraction to anyone but a physical chemist or a biochemist? Why should electrical potentials at the surface of the myocardial cell concern those who are not basic electrophysiolo-gists? The answers to all of these questions lie in the fact that virtually every important physiological, pharmacological, or pathological change in cardiac function arises from alterations in the physical and chemical processes that are responsible for the heartbeat. Although it remains fashionable to consider the heart as a muscular pump, this organ is much more than a hollow viscus that provides mechanical energy to propel blood through the vasculature. It is an intricate biological machine that contains, within each cell, a complex of control and effector mechanisms. Both the strength of cardiac contraction and its electrical control are modulated by alterations in one or more of these cellular mechanisms, which are involved in the fundamental processes of excitability, excitation-contraction coupling, and contraction. This text is written for medical students and graduate students in the biological sciences, and for the physician who would like to find a simplified exposition of our current understanding of the physiological and biophysical basis of cardiac function. Therefore, this book is intended to provide a synoptic view of our present knowledge in this rapidly expanding area. The major emphasis is on the relationships between the biochemical properties of individual constituents of the myocardial cell, the biophysics of cardiac muscle function, and the performance of the intact heart. The task of relating these different aspects of cardiac function to each other has required much selectivity and, undoubtedly, an excess of simplification and speculation. There can be no doubt that much of this conceptual material will become invalid as our knowledge of cardiac function advances. This is, after all, the lesson taught to us by the history of science. The early neurophysiologists who tried to understand nerve conduction as the passage of fluid down hollow tubes were trying to explain physiological phenomena in terms of the limited biophysical knowledge of their time. With the development of an understanding of animal electricity, the focus in neurophysiology shifted to studies of the electrical properties of the nervous system, and attempts were made to explain phenomena such as neuron-to-neuron communication and memory in terms of electrical circuitry. More recently the enormous advances in our knowledge of chemical transmitters and the potential for information storage as newly synthesized mac-romolecules have cast doubt on many of the theories of the great neurophysiologists of the last century. Yet these were not unintelligent scientists. They were.