Energetics of the Heart

Abstract

A new measure of the total mechanical energy (TME) generated by ventricular contraction was proposed to be quantified by a specific area in the pressure-volume (P-V) diagram that is bounded by the end-systolic and end-diastolic P-V relations and the systolic P-V trajectory. This area is called the systolic P-V area (PVA), interchangeably used with TME. We found in the left ventricle of the excised, cross-circulated dog heart preparation that PVA correlated linearly with myocardial O2 consumption (\( {V_{{o_2}}} \)) regardless of loading conditions in a stable contractile state. The load-independent linear \( {V_{{o_2}}} \)-PVA relation was elevated in a parallel manner by positive inotropic interventions, primarily due to an increased \( {V_{{o_2}}} \)for the augmented excitation-contraction coupling. The slope of the \( {V_{{o_2}}} \)-PVA relation can be considered to reflect inversely the efficiency of energy conversion to PVA from the excess \( {V_{{o_2}}} \)above unloaded \( {V_{{o_2}}} \). This efficiency is primarily the product of the oxidative phosphorylation efficiency from \( {V_{{o_2}}} \)to ATP and the contractile machinery efficiency from ATP to PVA. Thus, the \( {V_{{o_2}}} \)PVA relation seems a promising tool for the anlayses of cardiac energetics and mechanoenergetic coupling.