Regulation of Cardiac Output

Cardiac output, by its very name is ‘cardio-centric’. The implication is that it is the function of the heart that determines blood flow (corde primum movens). A functional heart is undoubtedly necessary, but itself insufficient for life-sustaining blood flow or cardiac output. This is well illustrated by the Guytonian super-imposition of the cardiac function and venous return curves. Cardiac output is a dependent variable. Conventional teaching indicates that preload, afterload and contractility (and heart rate) are the independent variables. These concepts will be addressed in this chapter. Two common clinical scenarios, acute fluid administration and heart failure following myocardial infarction are discussed to highlight these concepts.