Left ventricular systolic resistance in rats with hypertension and hypertrophy

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 (r² = 0.8257; P < 0.0001); Q_max^triQ = 2.4053 + 0.9767 × Q_max^mQ (r² = 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.

Temporal changes in cardiac force- and flow-generation capacity, loading conditions, and mechanical efficiency in streptozotocin-induced diabetic rats

Diabetes mellitus may result in impaired cardiac contractility, but the underlying mechanisms remain unclear. We aimed to investigate the temporal alterations in cardiac force- and flow-generation capacity and loading conditions as well as mechanical efficiency in the evolution of systolic dysfunction in streptozotocin (STZ)-induced diabetic rats. Adult male Wistar rats were randomized into control and STZ-induced diabetic groups. Invasive hemodynamic studies were done at 8, 16, and 22 wk post-STZ injection. Maximal systolic elastance (Emax) and maximum theoretical flow (Qmax) were assessed by curve-fitting techniques, and ventriculoarterial coupling and mechanical efficiency were assessed by a single-beat estimation technique. In contrast to early occurring and persistently depressed Emax, Qmax progressively increased with time but was decreased at 22 wk post-STZ injection, which temporally correlated with the changes in cardiac output. The favorable loading conditions enhanced stroke volume and Qmax, whereas ventriculoarterial uncoupling attenuated the cardiac mechanical efficiency in diabetic animals. The changes in Emax and Qmax are discordant during the progression of contractile dysfunction in the diabetic heart. In conclusion, our study showed that depressed Qmax and cardiac mechanical efficiency, occurring preceding overt systolic heart failure, are two major determinants of deteriorating cardiac performance in diabetic rats.

Factors controlling cardiac myosin-isoform shift during hypertrophy and heart failure

Myosin is a molecular motor, which interacts with actin to convert the energy from ATP hydrolysis into mechanical work. In cardiac myocytes, two myosin isoforms are expressed and their relative distribution changes in different developmental and pathophysiologic conditions of the heart. It has been realized for a long time that a shift in myosin isoforms plays a major role in regulating myocardial contractile activity. With the recent evidence implicating that alteration in myosin isoform ratio may be eventually beneficial for the treatment of a stressed heart, a new interest has developed to find out ways of controlling the myosin isoform shift. This article reviews the published data describing the role of myosin isoforms in the heart and highlighting the importance of various factors shown to influence myosin isofrom shift during physiology and disease states of the heart.