THEORETICAL MAXIMAL FLOW OF THE LEFT-VENTRICLE IS SENSITIVE TO CHANGEIN VENTRICULAR AFTERLOAD

Systolic mechanical behavior of the ventricular pump can be quantified by both maximal systolic elastance and theoretical maximal flow. How sensitive these two model parameters are to changes in loading conditi ons has never been examined, however. The aim of the study is to deter mine the roles of these two parameters in the perturbation of ventricu lar loads. The loading conditions are altered by the use of methoxamin e, a specific alpha(1)-selective adrenergic agonist. Left ventricular pressure and ascending aortic flow waves in male Fischer 344 rats are measured by a high-fidelity pressure sensor and electromagnetic flow p robe, respectively. Isovolumetric pressure of the left ventricle is es timated from the instantaneous pressure of an ejecting contraction by a curve-fitting technique. The two parameters that characterize systol ic pumping mechanics of the left ventricle are inferred by making use of an elastance-resistance model. Results in this study show that the theoretical maximum flow, the amount of outflow generated by the ventr icle if it were to eject under zero load condition, is sensitive to ch ange in ventricular afterload. On the contrary, the maximal systolic e lastance is independent of loading conditions in a given constant cont ractile state of the ventricle. It is believed that afterload-dependen t behavior of the theoretical maximal flow is the major factor respons ible for the poor predictive performance of the elastance-resistance m odel. (C) 1998 Academic Press.