Linear O₂ Use-Pressure-Volume Area Relation from Curved End-Systolic Pressure-Volume Relation of the Blood-Perfused Rat Left Ventricle

抄録

We measured rat left ventricular pressure, volume, and oxygen consumption (=arteriovenous oxygen content difference×coronary flow) to establish a new evaluation of its mechanoenergetics in the whole heart preparation by using the cross-circulation method. We obtained a curved end-systolic pressure-volume relation in contrast to a linear end-systolic pressure-volume relation in dogs, rabbits, and humans. However, we obtained a linear oxygen consumption per beat (VO₂)-systolic pressure-volume area (PVA, a measure of left ventricular total mechanical energy per beat) relation as in other species. Thus PVA can be a good index for assessing rat left ventricular mechanoenergetics. The VO₂ intercept and slope of the linear VO₂-PVA relation correspond to those in other species. Intracoronary calcium elevated the curved end-systolic pressure-volume relation and significantly increased PVA at 0.15 ml/g of left ventricular end-diastolic volume (PVA_0.15) by 50%. Calcium also significantly increased the VO₂ intercept of the VO₂-PVA relation by 30% without a change in its slope. We conclude that the rat left ventricular end-systolic pressure-volume relation is curved, but the VO₂-PVA relation is linear, and that the VO₂ intercept is mainly composed of PVA-independent VO₂, presumably VO₂ for Ca²⁺ handling in the excitation-contraction coupling and basal metabolism. Therefore we propose PVA at an appropriate left ventricular volume and the VO₂ intercept as good rat left ventricular mechanoenergetic indexes despite the nonlinearity of the end-systolic pressure-volume relation.