Estimation of Cardiac Performance and Efficiency during Aortic Occlusion and Induced Muscular Activity.

• Augmentation of external work of the heart due to an increase of blood pressure is accompanied by a greater increase of oxygen consumption (QOo) than increase of work due to an elevation of cardiac output." Thus the calculated cardiac efficiency, or ratio between the external cardiac work and oxygen consumption, decreases in the first case and either remains unchanged or increases in the second. It is suggested that this difference might be explained as follows: 1. The type of metabolism during pressure-work could be different from that during flow-work. 2. The usual formula for calculation of cardiac efficiency takes into account only the external work performed during the isotonic period while the oxygen consumption is calculated for the whole cardiac cycle, including the isovolumic period. It was assumed therefore that it is necessary to relate the QO2 to the total amount of energy developed by the left ventricle throughout the isotonic as well as the isovolumic period.