Sharir T, Feldman M D, Haber H, Feldman A M, Marmor A, Becker L C, Kass D A
Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, MD 21268.
Circulation. 1994 May;89(5):2045-53. doi: 10.1161/01.cir.89.5.2045.
Noninvasive cardiac-specific analysis of contractile function in patients with dilated heart failure remains problematic. This study tests whether maximal power divided by the square of end-diastolic volume (PWRmx/EDV2, or preload-adjusted PWRmx) can provide such assessment.
To validate the load insensitivity of the PWRmx index and determine its response to contractile change, 24 subjects with chronic dilated cardiomyopathy underwent invasive pressure-volume catheterization study using the conductance catheter technique. Preload was transiently reduced by 30% using balloon occlusion of the inferior vena cava, and afterload impedance was lowered by 50%, induced by a bolus injection of nitroglycerin. Contractile state was varied by intravenous dobutamine, verapamil, or esmolol. PWRmx was calculated from the simultaneous product of ventricular pressure and rate of volume change (dV/dt), the latter derived from the volume catheter signal. PWRmx varied directly with preload but was minimally influenced by afterload. However, PWRmx/EDV2 was not significantly altered by either loading change. PWRmx/EDV2 did vary with contractility, correlating closely with changes in the end-systolic pressure-volume relation (r = .91, P < .001). To test the noninvasive application of this index, 12 additional patients were studied, with PWRmx/EDV2 derived from nuclear ventriculography combined with a novel method to measure central arterial pressures. Subjects received intravenous nitroprusside or dobutamine in random order. Ejection fraction increased similarly with both agents (+42.9 +/- 8.9% for dobutamine and +29.4 +/- 5.3% for nitroprusside, both P < .01). In contrast, PWRmx/EDV2 did not significantly change with nitroprusside but increased by 126 +/- 16.1% with dobutamine (P < .01).
Preload-adjusted PWRmx is a steady-state index of ventricular systolic function that is sensitive to inotropic state and minimally influenced by physiological changes in afterload impedance or volume load. It appears useful for noninvasive cardiac-specific analysis of acute drug effects.
对扩张型心力衰竭患者的收缩功能进行无创性心脏特异性分析仍然存在问题。本研究测试最大功率除以舒张末期容积的平方（PWRmx/EDV2，即预负荷调整后的PWRmx）是否能提供这样的评估。
为验证PWRmx指数对负荷的不敏感性并确定其对收缩变化的反应，24例慢性扩张型心肌病患者采用电导导管技术进行了有创压力-容积导管检查研究。通过球囊闭塞下腔静脉使预负荷短暂降低30%，并通过静脉推注硝酸甘油使后负荷阻抗降低50%。通过静脉注射多巴酚丁胺、维拉帕米或艾司洛尔改变收缩状态。PWRmx由心室压力与容积变化率（dV/dt）的同步乘积计算得出，后者由容积导管信号得出。PWRmx与预负荷直接相关，但受后负荷的影响最小。然而，PWRmx/EDV2并未因任何一种负荷变化而发生显著改变。PWRmx/EDV2确实随收缩性而变化，与收缩末期压力-容积关系的变化密切相关（r = 0.91，P < 0.001）。为测试该指数的无创应用，又对12例患者进行了研究，PWRmx/EDV2由核素心室造影结合一种测量中心动脉压的新方法得出。受试者随机接受静脉注射硝普钠或多巴酚丁胺。两种药物使射血分数均有相似程度的增加（多巴酚丁胺组为+42.9±8.9%，硝普钠组为+29.4±5.3%，均P < 0.01）。相比之下，PWRmx/EDV2在使用硝普钠时无显著变化，但在使用多巴酚丁胺时增加了126±16.1%（P < 0.01）。
预负荷调整后的PWRmx是心室收缩功能的一个稳态指标，对变力状态敏感，受后负荷阻抗或容积负荷的生理变化影响最小。它似乎对急性药物效应的无创性心脏特异性分析有用。
