Fan D, Soei L K, Sassen L M, Krams R, Verdouw P D
Thoraxcenter, Erasmus University Rotterdam, The Netherlands.
Cardiovasc Res. 1995 Mar;29(3):428-37.
Oxygen consumption (MVO2) of stunned myocardium is relatively high compared to, and poorly correlated with, systolic contractile function. The aim of this study was to investigate whether an increased afterload dependency, induced by the decreased contractility of the stunned myocardium, contributes to the large variability in the mechanical efficiency data.
In 13 anaesthetised open thorax pigs undergoing two cycles of 10 min occlusion of left anterior descending coronary artery and 30 min reperfusion, segment shortening, the slope of end systolic pressure segment length relationship (Ees), external work (EW, derived from the area inside the left ventricular pressure segment length loop), the efficiency of energy conversion (EET, = EW/PLA x 100%, where PLA = total pressure-segment length area), mechanical efficiency (EW/MVO2), and their dependency on left ventricular end systolic pressure (Pes) were determined before and after induction of stunning, and during subsequent inotropic stimulation with dobutamine (1 and 3 micrograms.kg-1.min-1 over 15 min).
The stunning protocol not only caused significant decreases in segment shortening, external work, energy conversion efficiency, and EW/MVO2 but also increased the afterload dependency of these variables. Before stunning an increase in Pes from 100 to 160 mm Hg decreased segment shortening from 18(SEM 1)% to 14(2)% (P > 0.05) and increased external work from 206(18) to 254(32) mm Hg.mm (P < 0.05). After induction of stunning the same increase in Pes caused a decrease in segment shortening from 9.5(1.8)% to -4.6(2.1)% (P < 0.05) and in external work from 149(21) to -11(10) mm Hg.mm (P < 0.05). The afterload dependency of the PLA was not altered by stunning, but the afterload dependency of energy conversion efficiency increased, since efficiency decreased from 67(3)% to 59(5)% as Pes was increased from 100 to 160 mm Hg before stunning, but from 57(5) to -7(5)% after induction of stunning (P < 0.05). Furthermore, the same increase in Pes resulted in an 8% decrease of EW/MVO2 before stunning and 107% after induction of stunning. Infusion of dobutamine not only restored segment shortening, external work, energy conversion efficiency, and EW/MVO2 of the stunned myocardium, but also attenuated their afterload dependency to pre-stunning levels.
Myocardial stunning increases the afterload dependency of segment shortening, external work, energy conversion efficiency, and mechanical efficiency, which can be attenuated by inotropic stimulation with dobutamine. However, the decrease in left ventricular end systolic pressure, which accompanies the induction of stunning, counteracts the decrease in these variables. These two mechanisms can explain most of the reported scatter in mechanical efficiency.
与收缩期收缩功能相比，顿抑心肌的氧耗（MVO2）相对较高，且与收缩期收缩功能的相关性较差。本研究的目的是调查顿抑心肌收缩力降低所导致的后负荷依赖性增加是否会导致机械效率数据的巨大变异性。
对13只开胸麻醉猪进行两个周期的实验，即左前降支冠状动脉闭塞10分钟，再灌注30分钟。在诱发顿抑前、诱发顿抑后以及随后用多巴酚丁胺（1和3微克·千克-1·分钟-1，持续15分钟）进行变力刺激期间，测定节段缩短、收缩末期压力-节段长度关系（Ees）的斜率、外功（EW，由左心室压力-节段长度环内的面积得出）、能量转换效率（EET，=EW/PLA×100%，其中PLA=总压力-节段长度面积）、机械效率（EW/MVO2）及其对左心室收缩末期压力（Pes）的依赖性。
顿抑方案不仅导致节段缩短、外功、能量转换效率和EW/MVO2显著降低，还增加了这些变量的后负荷依赖性。在顿抑前，Pes从100毫米汞柱增加到160毫米汞柱，节段缩短从18（标准误1）%降至14（2）%（P>0.05），外功从206（18）增加到254（32）毫米汞柱·毫米（P<0.05）。诱发顿抑后，相同的Pes增加导致节段缩短从9.5（1.8）%降至-4.6（2.1）%（P<0.05），外功从149（21）降至-11（10）毫米汞柱·毫米（P<0.）。PLA的后负荷依赖性未因顿抑而改变，但能量转换效率的后负荷依赖性增加，因为顿抑前Pes从100毫米汞柱增加到160毫米汞柱时，效率从67（3）%降至59（5）%，而诱发顿抑后从57（5）%降至-7（5）%（P<0.05）。此外，相同的Pes增加导致顿抑前EW/MVO2降低8%，诱发顿抑后降低107%。输注多巴酚丁胺不仅恢复了顿抑心肌的节段缩短、外功、能量转换效率和EW/MVO2，还将它们的后负荷依赖性减弱至顿抑前水平。
心肌顿抑增加了节段缩短、外功、能量转换效率和机械效率的后负荷依赖性，这可以通过多巴酚丁胺的变力刺激来减弱。然而，顿抑诱发时伴随的左心室收缩末期压力降低抵消了这些变量的降低。这两种机制可以解释大多数报道的机械效率离散情况。
