Reviews of Educational Material  |   April 2016
The Heart and Circulation: An Integrative Model
Author Notes
  • Albany Medical Center, Albany, New York.
  • (Accepted for publication October 25, 2015.)
    (Accepted for publication October 25, 2015.)×
Article Information
Reviews of Educational Material / Cardiovascular Anesthesia
Reviews of Educational Material   |   April 2016
The Heart and Circulation: An Integrative Model
Anesthesiology 4 2016, Vol.124, 976-977. doi:10.1097/ALN.0000000000000977
Anesthesiology 4 2016, Vol.124, 976-977. doi:10.1097/ALN.0000000000000977
The concept that the heart is a pressure-generating pump propelling the blood through the systemic and pulmonary circulations is one of the fundamental principles of cardiovascular physiology, so axiomatic, that it is difficult to imagine it will ever be challenged. And yet, in this age of evidence-based medicine, even this seemingly inviolable tenet has been put to the test and surprisingly found to be less than foolproof.
This book is a thoughtful, stimulating, and ultimately challenging reevaluation of the traditional heart-as-a-pump concept, referred to as the “cardiocentric” model of cardiovascular physiology. In its place, the author presents a systematic, deliberate, and convincing evidence that the energy for blood propulsion arises at the periphery in the microvascular beds and in turn proposes an alternative, “hemocentric” model of circulation where the heart rhythmically interrupts the flow of blood and assumes the role of an impedance rather than of a pressure-propulsion pump.
In the first part of the book (10 chapters), a detailed review of the early embryonic circulation is given. While this material may be of less interest to a busy clinician, it provides important evidence in support of the proposed model to basic scientists and neonatologists. A refreshing highlight is the section on comparative phylogeny where, in place of the pressure-propulsion model, the evolutionary/biological model of circulation is introduced (Ch. 11 and 12). The validity of the proposed model is confirmed by comparing the key developmental stages of the invertebrate, mammalian, and avian species.
In the second part of the book, the mature circulation is discussed, beginning with a penetrating study of the functional morphology of the heart. A brief historic overview of “men and ideas” that shaped this fascinating field is given, from Leonardo da Vinci and R. Lower to J. Pettigrew-Bell. It includes more recent developments and research methods that confirm the unique lemniscate pattern of myocardial wall architecture, demonstrated by Pettigrew-Bell well over a century ago. The fact that the archetypal form of the heart is a vortex, developed in the course of evolution on account of the heart’s damming-up function, supports the basic thesis of the book that the heart is an organ of impedance. The saying by J. Pettigrew-Bell, that the architectural plan of the heart is a “Gordian knot” holding the key to its function, has no doubt began to be unraveled (Ch. 13).
In the remainder of the book, further proof from a variety of clinical and experimental scenarios is given, such as from the field of exercise physiology, where during peak exertion cardiac output in highly trained athletes increases up to six times above the baseline, and on account of rapid heart rate and shortened diastole, markedly exceeds the theoretical pumping capacity of the heart. To make up for the deficit, the concept of a “muscle pump” was proposed decades ago but is rapidly losing ground due to the lack of firm experimental evidence (Ch. 17).
The final chapters may be of particular interest to practitioners working in the field of cardiovascular anesthesia. First, the hemodynamic significance of aortic occlusion is discussed in light of the proposed model (Ch. 18). Should the heart be a pressure-propulsion pump, one would expect not only a significant drop in pressure distally to the applied aortic clamp but also a significant drop in cardiac output, if not cardiovascular collapse. Such would be the case in a compliant hydraulic system driven by a pump. Contrary to expectation, tightly controlled experiments in dogs have shown that cardiac output actually increases by 20 to 40% during occlusion of the thoracic aorta. No wonder caval occlusion is so poorly tolerated, because the principal “motor,” i.e., the capillary beds returning the blood back to the heart is effectively disabled.
In chapter 19, the flow-restraining function of the heart is further explored in examples ranging from large arteriovenous fistulas to congenital heart defects with “short-circuited” circulation at the level of the heart and/or great vessels, as is the case in atrial and ventricular septal defects and patent ductus arteriosus. Finally, the penultimate chapter discusses the challenging physiology of single ventricle hemodynamics, which according to the author offers yet the strongest evidence in support of the autonomously moving blood paradigm (Ch. 20).
In the last chapter entitled “Blood as an Organ,” the synthesis of the proposed circulation model is reviewed in the light of comparative anatomy (Ch. 11) and phenomenology of the mature circulation. The author explores differential sensitivity to hypoxia between the pulmonary and systemic circulation and the role of red blood cells as “oxygen sensors” and regulators of flow in the microvascular beds during normal and pathologic states (such as septic shock). There is considerable evidence that the red blood cells can no longer be viewed as “storage containers” for hemoglobin passively distributed by the circulating blood but rather they must be seen as playing an active role in microcirculatory flow. In this context, the author posits a radical suggestion that the hitherto vague concept of “organ and tissue autoregulation” be expanded to comprise the macrocirculation, in the sense that the systemic and pulmonary capillary beds are the actual “motors” of the circulation. This is the ultimate challenge that the reader is given to ponder when confronted with the evidence presented in this book.
With The Heart and Circulation, Dr. Furst has commendably reviewed the origin and historical development of the heart-as-a-pump concept and amassed, as well, a very considerable weight of evidence undermining it and supporting an alternative model of the heart as an organ of impedance. This book will be particularly well received by all those who, like myself, experience a growing lack of confidence in the cardiocentric model of circulation. It is not necessary, however, to be a critic of the traditional paradigm to enjoy this book. Clinicians and researchers firmly committed to the cardiocentric model in any discipline or specialty will be challenged, if not fascinated, by the numerous inconsistencies and observations so eruditely brought to light by Dr. Furst.
In summary, I recommend this book to all open-minded cardiovascular physiology enthusiasts without reservation; it is destined to be a valuable resource for deepening the understanding of the circulation.
Anthony M. O’Leary, M.B.B.S., F.R.C.A., Albany Medical Center, Albany, New York.