The relationship between systolic pressure and stroke volume describes myocardial contractility

Abstract

To develop a method of measuring end-systolic elastance from information obtained outside the ventricle and thereby simplify its transduction. Prospective, within-animal comparative analysis. University-based laboratory study. Six mixed-breed dogs. Instrumentation included minor axis sonomicrometry, ascending aortic flow probe, aortic and ventricular pressure transducers, and constricting cuffs on the vena cavae and aorta. Elastance was determined from the equation PES = EES (VED - VES), where VED - VES is stroke volume and PES is end-systolic arterial pressure. EES was derived from both preload and afterload manipulation. Cardiac performance indices were calculated automatically by computer under conditions of varying load and inotropy. This extraventricular method of elastance calculation was compared by linear regression and analysis of variance to preload recruitable stroke work, traditional EES determination (using ventricular dimension instead of volume), and LVdP/dt at 50 mmHg. EES measured from the aortic sites correlated well with the other contractility indicators (p < 0.003 in all cases) and demonstrated more sensitivity and stability under loading manipulation than traditional EES. A strong relationship between the change in stroke volume and end-systolic ventricular diameter during acute aortic constriction (r = 0.924, p < 0.0001) was observed, and the mean r value for the individual outflow elastance measurements was 0.97 +/- 0.02. In this study, measurement of EES from the ventricular outflow tract during progressive aortic constriction produced results more consistent and descriptive than EES by traditional techniques and has the potential for obtaining elastance measurements from possibly less invasive techniques.