| Summary: | What drives the circulation? In this comprehensive review of existing circulation models, the conventional view that the heart is a pressure-propulsion pump is challenged. The existing models fail to explain an increasing number of observed circulatory phenomena. A unifying circulation model is proposed in which the blood, responding to metabolic demands of the tissues, is the primary regulator of cardiac output. This new model arises from accumulated clinical and experimental evidence. The heart, rather than being an organ of blood propulsion, assumes a secondary role and generates pressure by impeding the flow of blood. This is supported by examples from the fields of early embryonic circulation, comparative phylogeny, functional morphology, exercise physiology and a range of clinical scenarios. The Heart and Circulation: An Integrative Model offers a paradigm shift in the understanding of circulatory phenomena. It will become a valuable resource for all those clinicians, researchers, educators and students who, having been confronted with the paradox of the circulation, are looking for a broader interpretation.
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