Efficiency of Cardiac Contraction in Ischemic Heart Studied in Conscious Dogs

我们研究了自然应力如何影响清醒的狗在控制条件下，运动和左心室功能不全的心室收缩效率。我们评估了心室收缩的效率及其与动脉系统的最佳负荷和最佳心脏的耦合。最佳负荷被定义为从给定心室提取最大功的负荷。最佳心脏被定义为以最小的单位时间耗氧量满足外周需求的心脏。在静止的控制条件下，动脉系统从给定的心脏提取超过95%的最大外部功。同时，心脏以几乎最低的氧气消耗向外周系统提供流量。通过锻炼，心率和心输出量几乎增加了一倍。收缩末期弹性（Ees）和有效动脉弹性增加，而其比值保持不变。尽管血液动力学变化很大，心脏的外功接近其最大值。在外周需求急剧增加的情况下，心脏的耗氧量也接近最低值。心功能障碍的产生显著增加了心脏的耗氧量。然而，心脏的外功仍然接近其最大值。我们的结论是，正常的心脏产生最大的外部工作与最小的氧气消耗在运动期间以及在休息。左心室功能的恶化显著降低了这些最佳状态。

We investigated how natural stresses affects efficiency of ventricular contraction in conscious dogs under the control condition, exercise and left ventricular dysfunction. We evaluated efficiency of ventricular contraction and its coupling with the arterial system in terms of optimal load and optimal heart. The optimal load is defined as that which extracts maximal work from a given ventricle. The optimal heart is defined as that which meets peripheral demand with minimum oxygen cost per unit time. Under the control condition at rest, the arterial system extract more than 95% of maximal external work from a given heart. At the same time, the hearts supplied flow to the peripheral system with a nearly minimum oxygen cost. With exercise, heart rate and cardiac output were nearly doubled. Both end-systolic elastance (Ees) and effective arterial elastance were increased while their ratio remained unchanged. Despite large changes in hemodynamics, external work of the heart was close to its maximal value. The oxygen consumption of the heart was also close to minimum in the presence of dramatically increased peripheral demand. Creation of cardiac dysfunction significantly increased the oxygen consumption of the heart. The external work of the heart, however, remained close to its maximal values. We conclude that the normal heart generates maximal external work with minimum oxygen cost during exercise as well as at rest. Deterioration of left ventricular function significantly lowers these optimalities.