Determinants of cardiac performance.

Sequential experimental studies are reviewed which, when properly integrated, confirm the concept that the responses of the ventricles, however measured, are determined by the initial length of fibers, provided that the functional state of the myocardium is not altered. Some of the established factors are discussed which may obscure the evidence that this basic law is of importance under normal and pathologic conditions. D URING the past 50 years progress in the study of heart disease has been achieved over different pathways.1 Among these is the clinical application of instrumentations and technics originally designed in, and limited to, physiologic laboratories. Since my entry into medical school in 1901 I have witnessed the successive employment of sphygmographs, phlebographs, apex beat recorders, sphygmomanometers, plethys-mographs, roentgenographs, electrocardio-graphs, and phonocardiographs. Some of these have not survived the dictates of experimental-fashions and are known to the present generation only as museum pieces or text figures,2 if at all. They were retired from the armamen-tarium of clinicians because the information gained did not appear commensurate with the time and effort required for their proper use. With the development of high fidelity pressure recorders in laboratories and the demonstrated safety of arterial punctures3 and cardiac cathe-terization in hospitals4 we have entered an era in which circulatory derangements are being intensively studied through the interpretation of cardiac outputs and of pressure pulses recorded directly from the cardiac chambers and large vessels. The interpretation of circulatory dynamics by such procedures requires not only a comparison of data from human subjects in health and disease, but also the utilization of information derived from more controllable experiments on animals. We can obviously not hope to comprehend the processes through 485 which we die unless we understand the mechanisms which keep organisms alive. The purposes of this review are (1) to restate briefly some important experimental results on cardiac performance, (2) to reexamine concisely the deductions, theories and concepts of cardiac behavior to which they have given rise, and (3) to attempt a resynthesis of evidence into a modern physiologic concept of myocardial regulation. Such a process of "modernization" involves a divorcement of factual data from theories and the integration of successive discoveries with classical ones of the past. When this is done it frequently happens, as in this instance, that very old laws of cardiac behavior have merely been given more extended applications, rather than that essentially new ones have been …