Quantification of cardiac pumping mechanics in rats by using the elastance–resistance model based solely on the measured left ventricular pressure and cardiac output

The cardiac pumping mechanics can be characterized by both the maximal systolic elastance (E(max)) and theoretical maximum flow (Q(max)), which are generated using an elastance–resistance model. The signals required to fit the elastance–resistance model are the simultaneously recorded left ventricular (LV) pressure and aortic flow (Q(m)), followed by the isovolumic LV pressure. In this study, we evaluated a single-beat estimation technique for determining the E(max) and Q(max) by using the elastance–resistance model based solely on the measured LV pressure and cardiac output. The isovolumic LV pressure was estimated from the measured LV pressure by using a non-linear least-squares approximation technique. The measured Q(m) was approximated by an unknown triangular flow (Q(tri)), which was generated by using a fourth-order derivative of the LV pressure. The Q(tri) scale was calibrated using the cardiac output. Values of E(max)(triQ) and Q(max)(triQ) obtained using Q(tri) were compared with those of E(max)(mQ) and Q(max)(mQ) obtained from the measured Q(m). Healthy rats and rats with chronic kidney disease or diabetes mellitus were examined. We found that the LV E(max) and Q(max) can be approximately calculated using the assumed Q(tri), and they strongly correlated with the corresponding values derived from Q(m) (P < 0.0001; n = 78): E(max)(triQ) = 51.9133 + 0.8992 × E(max)(mQ) (r(2) = 0.8257; P < 0.0001); Q(max)(triQ) = 2.4053 + 0.9767 × Q(max)(mQ) (r(2) = 0.7798; P < 0.0001). Our findings suggest that the proposed technique can be a useful tool for determining E(max) and Q(max) by using a single LV pressure pulse together with cardiac output.