Effect of Flow‐Independent Reduction of Metabolism on Regional Myocardial Clearance of 11C‐Palmitate
Effect of Flow‐Independent Reduction of Metabolism on Regional Myocardial Clearance of 11C‐Palmitate
复制标题
流量无关的代谢减少对 11C-棕榈酸酯局部心肌清除的影响
作者：
R. Lerch;S. Bergmann;H. Ambos;M. Welch;M. Ter;B. Sobel
最近的研究表明，连续正电子发射断层扫描后，早期清除心肌活性静脉碳-11（11 C）-棕榈酸酯减少缺血区域。为了确定清除率降低是否反映了标记底物或其代谢物的洗脱减少，或反映了标记脂肪酸代谢减少，我们在两种条件下表征了限制氧供应对体内局部11 C清除率的影响：缺氧而不伴随流量减少和由流量减少（缺血）诱导的缺氧。在21只开胸犬的左冠状动脉前降支（LAD）中插入导管，并通过体外旁路系统进行灌注。在每只犬中，冠状动脉内注射11 C-棕榈酸酯后，用β-检测器探针记录两条局部时间-活性曲线（间隔90分钟）。在对照犬（n = 7）中，两项研究之间未进行干预。在实验犬中，在第二次注射11 C棕榈酸酯前15分钟通过减少LAD流量平均76%（缺血组，n = 7）或通过用静脉血以正常流速灌注LAD床来减少氧供应，导致氧含量平均减少66%（缺氧组，n = 7）。根据H2150洗脱测定的LAD灌注区的心肌血流量在对照组或缺氧组中均无变化，但在缺血组中平均减少64%（p< 0.025）。同样，对照犬的11 C清除率从第一项研究到第二项研究没有变化。然而，尽管维持血流，缺氧（p < 0.02）以及缺血本身（61%，p < 0.005），11 C清除率平均降低52%。因此，尽管灌注持续，但在缺氧区域，心肌提取11 C-棕榈酸酯后11 C-活性的清除率始终降低，这支持了以下假设：基于正电子发射断层扫描获得的局部时间-活性曲线的顺序和定量分析，可以在患者中检测到缺氧或缺血本身诱导的代谢衰减。
Recent studies with sequential positron-emission tomography have demonstrated that early clearance of activity from myocardium after i.v. carbon-11 (11C)-palmitate is decreased in regions of ischemia. To determine whether the reduced clearance is a reflection of decreased washout of labeled substrate or its metabolites, or a reflection of decreased metabolism labeled fatty acid, we characterized the effects of restricted oxygen supply on regional 11C clearance rates in vivo u'nder two conditions: hypoxia'without concomitant reduction of flow and hypoxia induced by reduction of flow (ischemia). In 21 open-chest dogs, the left anterior descending coronary artery (LAD) was cannulated and perfused by an extracorporal bypass system. In each dog two regional time-activity curves (90 minutes apart) were recorded with a β-detector probe after intracoronary injection of 11C-palmitate. In control dogs (n = 7), no intervention was imposed between the two studies. In the experimental dogs, oxygen supply was reduced 15 minutes before the second injection of 11Cpalmitate by either reducing LAD flow by an average of 76% (ischemia group, n = 7) or by perfusing the LAD bed at normal flow rate with venous blood, resulting in an average reduction in oxygen content of 66% (hypoxia group, n = 7). Myocardial blood flow in the LAD-perfused region determined based on washout of H2150 did not change in either'the control or hypoxia group, but decreased by an average of 64% (p< 0.025) in the ischemia group. Similarly, 11C clearance rates did not change from the first to the second study in control dogs. However, the, 11C clearance rate was reduced by an average of 52% with hypoxia despite maintenance of flow (p < 0.02) as well as by ischemia itself (61%, p < 0.005). Thus, clearance of 11C-activity after extraction of 11C-palmitate by myocardium is consistently reduced in regions rendered hypoxic despite persistence of perfusion, supporting the hypothesis that the metabolic attenuation induced by hypoxia or ischemia per se can be detected in patients based on sequential and quantitative analysis'of regional time-activity curves obtained by positron-emission tomography.