Hansen D E
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2170.
Am J Physiol. 1993 Feb;264(2 Pt 2):H423-32. doi: 10.1152/ajpheart.1993.264.2.H423.
Electrophysiological consequences of altering ventricular load (mechanoelectrical feedback) were characterized in an isolated canine heart preparation. A computerized servo pump system controlled left ventricular volume and allowed ventricular ejection against a simulated arterial load (3-element Windkessel model). In 12 ventricles, end-diastolic volume (Ved) was held constant (end-diastolic pressure 6-12 mmHg) as arterial resistance (R) was varied (0.5-12 mmHg.s.ml-1), but afterload-dependent changes in the monophasic action potential (MAP) were not observed despite a large stroke volume effect. In contrast, when R was held constant in eight ventricles while Ved was increased from 20 to 40 ml, the plateau phase of the MAP was abbreviated, the terminal portion of phase 3 repolarization was delayed, and MAP duration measured at 20, 70, and 90% repolarization decreased (P < 0.05). In six ventricles, immediate transitions from isovolumic to ejecting mode at constant Ved did not alter MAP duration, but the magnitude of early afterdepolarizations (EADs), observed during isovolumic beats at high Ved, was reduced with resumption of ventricular ejection. As stroke volume of the initial ejecting contraction was increased by stepwise reductions of R, the magnitude of the EADs decreased progressively. Thus altering ventricular afterload does not modulate action potential duration in ventricles subjected to elevated, physiological, or even greatly reduced levels of afterload, whereas diastolic filling to high Ved does. Under conditions that lead to reduced stroke volume and high end-systolic volume, EADs are produced that are virtually abolished when ventricular ejection fraction is normalized.
在离体犬心制备模型中，对改变心室负荷（机械电反馈）的电生理后果进行了研究。计算机控制的伺服泵系统可控制左心室容积，并使心室在模拟动脉负荷（三元风箱模型）下射血。在12个心室中，当动脉阻力（R）在0.5 - 12 mmHg·s·ml⁻¹范围内变化时，舒张末期容积（Ved）保持恒定（舒张末期压力6 - 12 mmHg），尽管每搏输出量有较大变化，但未观察到单相动作电位（MAP）的后负荷依赖性改变。相反，在8个心室中，当R保持恒定时，将Ved从20 ml增加到40 ml，MAP的平台期缩短，复极化3期的终末部分延迟，并且在复极化20%、70%和90%时测量的MAP持续时间缩短（P < 0.05）。在6个心室中，在恒定Ved下从等容模式立即转变为射血模式并未改变MAP持续时间，但在高Ved的等容搏动期间观察到的早期后去极化（EADs）的幅度，随着心室射血的恢复而降低。随着通过逐步降低R增加初始射血收缩的每搏输出量，EADs的幅度逐渐减小。因此，改变心室后负荷在心室后负荷升高、处于生理水平甚至大幅降低时，均不会调节动作电位持续时间，而舒张期充盈至高Ved时则会。在导致每搏输出量减少和收缩末期容积增加的情况下，会产生EADs，当心室射血分数恢复正常时，EADs几乎消失。
