LINEAR O-2 USE-PRESSURE-VOLUME AREA RELATION FROM CURVED END-SYSTOLICPRESSURE-VOLUME RELATION OF THE BLOOD-PERFUSED RAT LEFT-VENTRICLE

We measured rat left ventricular pressure, volume, and oxygen consumpt ion (=arteriovenous oxygen content difference X coronary flow) to esta blish a new evaluation of its mechanoenergetics in the whole heart pre paration by using the cross-circulation method. We obtained a curved e nd-systolic pressure-volume relation in contrast to a linear end-systo lic 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 ener gy per beat) relation as in other species. Thus PVA can be a good inde x for assessing rat left ventricular mechanoenergetics. The VO2 interc ept and slope of the linear VO2-PVA relation correspond to those in ot her species. Intracoronary calcium elevated the curved end-systolic pr essure-volume relation and significantly increased PVA at 0.15 ml/g of left ventricular end-diastolic volume (PVA(0.15)) by 50%. Calcium als o significantly increased the VO2 intercept of the VO2-PVA relation by 30% without a change in its slope. We conclude that the rat left vent ricular end-systolic pressure-volume relation is curved, but the VO2-P VA relation is linear, and that the VO2 intercept is mainly composed o f PVA-independent VO2, presumably VO2 for Ca2+ handling in the excitat ion-contraction coupling and basal metabolism. Therefore we propose PV A at an appropriate left ventricular volume and the VO2 intercept as g ood rat left ventricular mechanoenergetic indexes despite the nonlinea rity of the end-systolic pressure-volume relation.