Ventricular pressure-volume area (PVA) accounts for cardiac energy consumption of work production and absorption

We briefly review that ventricular systolic pressure-volume area (PVA) can predict changes in myocardial O₂ consumption (VO₂) associated with cardiac work production (positive work) and absorption (negative work). PVA represents the total mechanical energy of cardiac contraction as it is an integral of mechanical energy generated during systole in the cardiac chamber. We have shown that PVA linearly correlates with VO₂ under varied pre- and afterload conditions in the left ventricle of the excised cross- circulated canine heart preparation as well as other heart preparations of different species. PVA is the sum of external mechanical work (EW) and mechanical potential energy (PE) which is almost fully convertible to mechanical work without affecting VO₂. To compare the energetic effects of cardiac work production and absorption, we varied the timing of the servo pump motion relative to left ventricular (LV) contraction. When the pump fills the LV during diastole and sucks (allows ejection) during systole, cardiac work is produced by the heart, and hence EW > 0. When the pump fills the LV during systole and sucks during diastole, work is absorbed by the heart, and hence EW < 0. The pressure-volume loop rotates counterclockwise when EW > 0. It rotates clockwise when EW < 0. As the result, PVA (= PE + EW) > PE when EW > 0; PVA < PE when EW < 0. We found that VO₂ always linearly correlated with PVA regardless of the polarity of EW. Therefore, PVA is the unique determinant of VO₂ in a cardiac chamber in a stable contractility.