Spring 2020 – Quantifying Guyton’s Cardiac Output and Venous Return

Guyton’s cardiac output-venous return curves have become a common tool for students, clinical investigators, and physiologists to conceptualize the complex interaction of cardiac output (CO) and venous return (VR). An algebraic formula predicting Guyton’s venous return has provided critical insights into the role of mechanical properties of the systemic vasculature. However, attempts to provide insights into Guyton’s cardiac output curve has been limited, because conventional model equations include nonlinearities that must be solved numerically. In a different approach, investigators reported that general algebraic formulas for hemodynamic variables can be derived from linearizing the equations characterizing the standard minimal closed-loop model. Therefore, the purpose of the present work is to use the linearized minimal closed-loop model to derive a general algebraic formula for the slopes and intercepts of Guyton’s CO-VR in terms of mechanical properties of the cardiovascular system. This novel tool already provides a surprising insight that, contrary to conventional belief, the slope of Guyton’s CO curve is not influenced by contractility of the left ventricle. This project will provide a novel tool for medical students and physiologists that can be used in textbooks and clinical settings.