Analysis of the Several Factors Regulating the Performance of the Heart

Abstract

End-diastolic volume is an important determinant in regulating the performance of the heart beat, but not the only one. Cardiac output, cardiac work and cardiac O2, consumption can vary among themselves in a manner incompatible with the thesis that end-diastolic volume alone regulates all three. Other important factors which regulate the heart''s performance are (a) the after-load against which the heart contracts and (b) the extrinsic (and intrinsic) neurogenic and humoral factors controlling the contractile power of the heart, its tone, its heart rate and its systolic residue. In the intact animal, the interplay of these factors sets the cardiac output, the work which the heart performs, and the metabolic changes which produce the energy required to do this work. No one of these factors alone gives an adequate picture of the heart''s performance.