LEFT VENTRICULAR TIME-VARYING ELASTANCE

左心室(LV)功能的评估仍然是一个困难的问题。 临床实践和生理研究中存在的问题。数据来自 离体犬心脏提示左心室表现为弹性结构。 在收缩期间以可预测的方式僵硬，因此，它可以 被描述为时变弹性。该项目的目标是 检验这一假说描述LV之间关系的能力 原位心脏的收缩压和容量；并研究两个 我们从时间上推导出的评估LV性能的新方法 不同弹性假设。第一种方法涉及关系 LV压力上升峰值速率(dp/dt-max)与LV 舒张末容量。我们将测试这一假设，并由我们的 初步数据表明，这种关系是线性的，对变化不敏感 在加载条件下，对变力状态非常敏感。其次，我们 将评估一种新的计算E-max的方法，即LV的斜率 收缩末期压力-体积关系，使用从 时变弹性假设，并得到初步数据的支持。这 将E-max描述为左心室收缩末期dp/dt-max的函数 和舒张末容量，以及收缩末期的时间。因此，E-max可以是 根据一组条件下的测量结果确定，避免 需要改变负荷条件以产生一定范围的LV收缩末期 压力-体积点。 这些研究将在长期使用仪器的狗身上进行。 测量LV压力的微型压力计和3对超声晶体 以确定LV容量。主动脉血流量将用 电磁流量探头。LV压力和容量将随CAVAL而变化 闭塞。肌力状态将通过多巴酚丁胺输注改变，而 甲氧胺和右旋糖苷的输注将改变负载条件 通过短暂阻断降主动脉。等容节拍将 是由升主动脉一过性完全闭塞造成的。 这些研究将提供有关LV描述符的新信息 原位心脏收缩功能与两种评价左心室的新方法 可能与加载条件无关的性能。

The evaluation of left ventricular (LV) performance remains a difficult problem in clinical practice and physiologic investigation. Data from isolated canine hearts suggest that the LV behaves as an elastic structure that stiffens in a predictable manner during systole, thus, it can be described as a time-varying elastance. The goals of this project are to test the ability of this hypothesis to describe the relation between LV systolic pressure and volume in the in situ heart; and to investigate two new methods of evaluating LV performance that we have derived from the time varying elastance hypothesis. The first method involves the relation between the peak rate of LV pressure rise (dP/dt-max) and the LV end-diastolic volume. We will test the hypothesis, supported by our preliminary data, that this relation is linear, insensitive to alterations in loading conditions, and very sensitive to inotropic state. Secondly, we will evaluate a new method of calculating E-max, the slope of the LV end-systolic pressure-volume relation, using a relation derived from the time-varying elastance hypothesis and supported by preliminary date. This relation describes E-max as a function of dP/dt-max, the LV end-systolic and end-diastolic volumes, and the time to end-systole. Thus E-max can be determined from measurements under a single set of conditions, avoiding the need to alter loading conditions to produce a range of LV end-systolic pressure-volume points. These studies will be carried out in dogs chronically instrumented with a micromanometer to measure LV pressure, and 3 pairs of ultrasonic crystals to determine LV volume. Aortic flow will be measured with an electromagnetic flow probe. LV pressure and volume will be varied by caval occlusions. Inotropic state will be altered by dobutamine infusion, while loading conditions will be varied by infusion of methoxamine and dextran and by transient occlusions of the descending aorta. Isovolumic beats will be produced by transient complete occlusion of the ascending aorta. These studies will provide new information on the descriptors of LV systolic function in the in situ heart and two new methods of evaluating LV performance that may be independent of loading conditions.