Effect of mean circulatory filling pressure and other peripheral circulatory factors on cardiac output.

I P ONE studies curves which depict the relationship of cardiac output to mean right atria1 pressure (one of the forms of Starling’s curves), it is obvious that, within the normal range of function of the heart, cardiac output can change tremendously while the right atria1 pressure changes only slightly. This fact led to the early belief that it is not the function of the heart itself which controls cardiac output but instead that cardiac output is controlled by the various factors in the peripheral circulatory system which regulate the return of blood to the heart. Though it is not entirely true that cardiac output is independent of the function of the heart (I), nevertheless, it is hoped to emphasize in the present paper the special importance of the peripheral circulatory factors which affect venous return. In order to do this, a mathematical circuit analysis of the closed circuit circulatory system has been made. This circuit analysis has been specifically simplified so that the factors derived would be amenable to experimental test. Two of the factors which have proved to be of importance, as shown both by this circuit analysis and by experimental data, are a) ‘capacitance’ and b) ‘mean circulatory filling pressure.’ As used in these studies the term capacitance means dV/dP or, in other words, the change in volume of a particular part of the circulatory system with each unit change in pressure. This term has been used in the present paper because there is at present no term in common usage in hydrodynamics which means dV/dP. This is different from the term ‘distensibility’ which is commonly used to mean dV/dP + V. The term mean circulatory filling pressure (MCFP) has been defined previously (2), and it means ,__-