Regulation of Cardiac Output

Abstract

Usually cardiac output is regulated mainly by the tissues, each regulating its own blood flow, cardiac output being the sum of the flows through all the peripheral tissues. The normal human heart under resting conditions can pump perhaps 12-15 l/min., and when stimulated by the autonomic system, perhaps 25-35 l/min. The cardiac output rarely rises to the maximum levels. Thus, the heart permits the cardiac output to be regulated at any value between zero and its permissive level. Otherwise it plays a secondary role unless it becomes too weak to meet the demands of the body. The 2 principal factors determining the rate of blood return to the heart from the peripheral circulation are the degree of vasodilatation of the peripheral vasculature, especially of veins but to a lesser extent arteries as well, and the degree of filling of the circulatory system, expressed as the mean systemic pressure. Either a decrease of resistance in the vasculature or an increase in the mean systemic pressure will increase cardiac output.