EFFECT OF EXERCISE ON LEFT VENTRICULAR-ARTERIAL COUPLING ASSESSED IN THE PRESSURE-VOLUME PLANE

The left ventricle (LV) and arterial system are nearly optimally coupl ed to produce stroke work (SW) at rest. However, the effect of exercis e on the coupling between the LV and arterial system has not been dire ctly determined. We evaluated 11 dogs who were instrumented to determi ne LV volume from three diameters. The LV end-systolic pressure (P(es) )-volume (V(es)) relation was determined by transient caval occlusion at rest and while the animals ran at 5-7 mph on a treadmill. During ex ercise, the P(es)-V(es) relation was shifted toward the left and the s lope [end-systolic elastance (E(es))] increased from 7.7 +/- 2.8 to 12 .7 +/- 4.2 (SD) mmHg/ml (P < 0.05). The arterial end-systolic elastanc e (E(a)), calculated as P(es) divided by stroke volume, increased duri ng exercise (8.8 +/- 3.0 to 10.9 +/- 4.7 mmHg/ml, P < 0.05). The ratio of E(es) to E(a) increased during exercise from 0.89 +/- 0.31 to 1.27 +/- 0.12 (P < 0.05). The portion of the pressure-volume area expresse d as SW increased during exercise from 0.63 +/- 0.07 to 0.69 +/- 0.10 (P < 0.05). After adrenergic blockade, the E(es)-to-E(a) ratio was not significantly altered during exercise (0.90 +/- 0.24 vs. 0.83 +/- 0.1 5, P = NS). At rest and during exercise, both with intact reflexes and after beta-adrenergic blockade, the ratio of E(es) to E(a) remained w ithin the range in which SW is >95% of maximum. We conclude that durin g exercise, beta-adrenergic stimulation shifts the LV P(es)-V(es) rela tion to the left with an increased slope. This more than offsets the i ncrease in E(a). Thus the LV and arterial system remain optimally coup led to produce SW both at rest and during exercise.