RELATION BETWEEN LEFT-VENTRICULAR OXYGEN-CONSUMPTION AND PRESSURE-VOLUME AREA IN CONSCIOUS DOGS

Background The relation between left ventricular (LV) oxygen consumpti on (MVo(2)) and pressure-volume area (PVA) developed in isolated heart s provides a powerful method to understand cardiac energetics. We inve stigated application of this relation to the intact circulation, deter mining its response to steady-state and transient load alterations and enhanced contractility in conscious animals. Methods and Results Eigh t dogs were instrumented to measure LV pressure (micromanometer), LV v olume (three sonomicrometers), and left circumflex and anterior descen ding coronary artery flows (ultrasonic flowmeter). Data were acquired after recovery from the surgery with the animals awake and unsedated. After administration of hexamethonium and atropine, steady-state loadi ng conditions were changed with phenylephrine or nitroprusside in four to five steps before and during the infusion of dobutamine (6 to 10 m u g.(-1)kg.(-1)min). MVo(2) and PVA obtained under steady-state condit ions were linearly correlated both before and during dobutamine. The M Vo(2)-PVA relation obtained on a beat-to-beat basis during transient c aval occlusion was less linear and not coincident with the steady-stat e relation. Dobutamine shifted the steady-state MVo(2)-PVA relation up ward in all hearts, increasing the MVo(2) axis intercept of the MVo(2) -PVA relation (P<.01). This intercept correlated with ventricular cont ractility assessed by the slope (E(es)) of the LV end-systolic pressur e-volume relation determined by caval occlusion (r=.76, P<.05). The sl ope of the MVo(2)-PVA relation increased with dobutamine in seven of e ight animals, with the inverse of the slope (representing contractile efficiency) being 31+/-6% during control and 24+/-6% after dobutamine (P=.06). Conclusions MVo(2) and PVA are linearly related during steady -state alterations in loading conditions in conscious dogs but not on a beat-by-beat basis during transient caval occlusion. Increase in con tractility by dobutamine produces an upward shift of the MVo(2)-PVA re lation.