THE RELATIONSHIP BETWEEN SYSTOLIC PRESSURE AND STROKE VOLUME DESCRIBES MYOCARDIAL-CONTRACTILITY

Objective: To develop a method of measuring end-systolic elastance fro m information obtained outside the ventricle and thereby simplify its transduction. Design: Prospective, within-animal comparative analysis. Setting: University-based laboratory study. Participants: Six mixed-b reed dogs. Interventions: Instrumentation included minor axis sonomicr ometry, ascending aortic flow probe, aortic and ventricular pressure t ransducers, and constricting cuffs on the vena cavae and aorta. Measur ements and Main Results: Elastance was determined from the equation P- ES = E(ES) (V-ED - V-ES), where V-ED - V-ES is stroke volume and P-ES is end-systolic arterial pressure. E(ES) was derived from both preload and afterload manipulation. Cardiac performance indices were calculat ed automatically by computer under conditions of varying load and inot ropy. This extraventricular method of elastance calculation was compar ed by linear regression and analysis of variance to preload recruitabl e stroke work, traditional E(ES) determination (using ventricular dime nsion instead of volume), and LVdP/dt at 50 mmHg, E(ES) measured from the aortic sites correlated well with the other contractility indicato rs (p < 0.003 in all cases) and demonstrated more sensitivity and stab ility under loading manipulation than traditional E(ES). A strong rela tionship between the change in stroke volume and end-systolic ventricu lar diameter during acute aortic constriction (r = 0.924, p < 0.0001) was observed, and the mean r value for the individual outflow elastanc e measurements was 0.97 +/- 0.02. Conclusions: In this study, measurem ent of E(ES) from the ventricular outflow tract during progressive aor tic constriction produced results more consistent and descriptive than E(ES) by traditional techniques and has the potential for obtaining e lastance measurements from possibly less invasive techniques. (C) 1995 by W.B. Saunders Company