Single-beat Estimation of the Ventricular Pumping Mechanics in Terms of the Systolic Elastance and Resistance

An elastance-resistance model has long been used to assess the systolic mechanical behavior of the ventricular pump under anin situ, open-chest experiment. However, there is difficulty in the clinical application of such a model because of the required isovolumetric signal that is obtained by occluding the ascending aorta in diastole. In this study, we determine the characteristics of an elastance-resistance model in the absence of isovolumetric measurement to quantify the physical properties of the left ventricle. A high-fidelity multisensor catheter was used to record the left ventricular pressure and ascending aortic flow in nine anaesthetized, closed-chest dogs. The isovolumetric pressure was estimated from the instantaneous pressure of an ejecting contraction by a curve-fitting technique. Thus, the parameters in the characterization of systolic pumping mechanics could be inferred by the used of fitting this elastance-resistance model. The results showed that the maximal systolic elastance was 7.3±2.8 mmHg and theoretical maximum flow was 494±194 ml s−1. These data were compatible with other reports in the literature. Moreover, in every dog studied the maximal systolic elastance was smaller than the end-systolic elastance which was determined by using the end-systolic pressure-volume relation. We suggested that an elastance-resistance model with theestimatedisovolumetric pressure has the potential to measure the intrinsic systolic mechanics of the left ventricle in a closed-chest cardiovascular system.