CURVILINEARITY OF LV END-SYSTOLIC PRESSURE-VOLUME AND DP DTMAX-END-DIASTOLIC VOLUME RELATIONS/

We investigated the effect of contractile state (CS) on the curvilinea rity of the left ventricular (LV) end-systolic pressure-volume (P(es)- V(es)) and the dP/dt(max)-end-diastolic volume (dP/dt(max)-V(ed)) rela tions in eight anesthetized open-chest dogs. LV volume was determined from three orthogonal diameters measured by sonomicrometry. The P(es)- V(es) relation and dP/dt(max)-V(ed) relation were assessed during tran sient vena caval occlusion and aortic constriction, while CS was alter ed with dobutamine. At all CS, both relations were linear when volumes were decreased by caval occlusion. However, at higher volumes obtaine d by aortic constriction, the relations became nonlinear. At enhanced CS, the nonlinearity of both the P(es)-V(es) relation and the dP/dt(ma x)-V(ed) relation increased. The dP/dt(max)-V(ed) relation began to de viate from linearity at larger volumes, but closer to baseline operati ng volume, than the P(es)-V(es) relation. The relation between end-sys tolic mean circumference stress and wall strain (sigma(es)-epsilon(es) ) was linear at control CS when the P(es)-V(es) relation was nonlinear but became nonlinear with enhanced CS. We conclude that both the P(es )-V(es) relation and the dP/dt(max)-V(ed) relation are nonlinear, satu rating at higher volumes. With increased CS, the nonlinearity of both relations increases. This CS-dependent curvilinearity of the P(es)-V(e s) relation is due to both CS-dependent nonlinearity of the sigma(es)- epsilon(es) relation (consistent with length-dependent activation) and geometric factors that alter the relation between P(es) and sigma(es) .