Control of cardiac output by regional blood flow distribution
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Most data indicate that cardiac output is normally controlled by the systemic circulation rather than by the heart. This manuscript extends that concept by analyzing the systemic circulation with a mathematical model comprised of two dissimilar blood flow channels. The concept and the model are not new and have, in fact, a strong anatomical and historical basis. However, re-examination using a quantitative, computerized analysis scaled to human dimensions is made in the face of new experimental data.
The crux of the model is that two parallel blood flow channels have dissimilar compliances. Regional blood flows distribute total blood volume between the two primary blood storage areas, where the blood is more or less effective in promoting venous return according to its location. Changes in cardiac output can theoretically be achieved solely by changes in arterial resistance, without alteration of venous compliance or resistance; this is the situation that is analyzed in detail.
The performance of the model was correlated with experimental data that describe the hemodynamic responses to thoracic aortic constriction, exercise, circulatory shock following endotoxin administration, and other situations. The correlation indicates that redistribution of blood flow following arterial resistance changes can theoretically have a very strong effect on the level of cardiac output, either in a direct causal role or in an ancillary role in conjunction with other, more dominant control mechanisms.
KeywordsCardiac Output Regional Blood Flow Aortic Constriction Total Blood Volume Circulatory Shock
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