Mutch W A, Ryner L N, Kozlowski P, Scarth G, Warrian R K, Lefevre G R, Wong T G, Thiessen D B, Girling L G, Doiron L, McCudden C, Saunders J K
Department of Anesthesia, University of Manitoba, Winnipeg, Canada.
Ann Thorac Surg. 1997 Sep;64(3):695-701. doi: 10.1016/s0003-4975(97)00634-6.
Neurocognitive deficits after open heart operations have been correlated to jugular venous oxygen desaturation on rewarming from hypothermic cardiopulmonary bypass (CPB). Using a porcine model, we looked for evidence of cerebral hypoxia by magnetic resonance imaging during CPB. Brain oxygenation was assessed by T2*-weighted imaging, based on the blood oxygenation level-dependent effect (decreased T2*-weighted signal intensity with increased tissue concentrations of deoxyhemoglobin).
Pigs were placed on normothermic CPB, then cooled to 28 degrees C for 2 hours of hypothermic CPB, then rewarmed to baseline temperature. T2*-weighted, imaging was undertaken before CPB, during normothermic CPB, at 30-minute intervals during hypothermic CPB, after rewarming, and then 15 minutes after death. Imaging was with a Bruker 7.0 Tesla, 40-cm bore magnetic resonance scanner with actively shielded gradient coils. Regions of interest from the magnetic resonance images were analyzed to identify parenchymal hypoxia and correlated with jugular venous oxygen saturation. Post-hoc fuzzy clustering analysis was used to examine spatially distributed regions of interest whose pixels followed similar time courses. Attention was paid to pixels showing decreased T2* signal intensity over time.
T2* signal intensity decreased with rewarming and in five of seven experiments correlated with the decrease in jugular venous oxygen saturation. T2* imaging with fuzzy clustering analysis revealed two diffusely distributed pixel groups during CPB. One large group of pixels (50% +/- 13% of total pixel count) showed increased T2* signal intensity (well-oxygenated tissue) during hypothermia, with decreased intensity on rewarming. Changes in a second group of pixels (34% +/- 8% of total pixel count) showed a progressive decrease in T2* signal intensity, independent of temperature, suggestive of increased brain hypoxia during CPB.
Decreased T2* signal intensity in a diffuse spatial distribution indicates that a large proportion of cerebral parenchyma is hypoxic (evidenced by an increased proportion of tissue deoxyhemoglobin) during CPB in this porcine model. Neuronal damage secondary to parenchymal hypoxia may explain the postoperative neuropsychological dysfunction after cardiac operations.
心脏直视手术后的神经认知缺陷与低温体外循环（CPB）复温期间颈静脉血氧饱和度降低有关。我们使用猪模型，通过磁共振成像寻找CPB期间脑缺氧的证据。基于血氧水平依赖效应（随着脱氧血红蛋白组织浓度增加，T2 *加权信号强度降低），通过T2 *加权成像评估脑氧合。
将猪置于常温CPB上，然后冷却至28℃进行2小时低温CPB，然后复温至基线温度。在CPB前、常温CPB期间、低温CPB期间每隔30分钟、复温后以及死亡后15分钟进行T2 *加权成像。成像使用带有主动屏蔽梯度线圈的布鲁克7.0特斯拉、40厘米孔径磁共振扫描仪。对磁共振图像的感兴趣区域进行分析，以识别实质缺氧情况，并与颈静脉血氧饱和度相关联。采用事后模糊聚类分析来检查像素遵循相似时间进程的空间分布感兴趣区域。关注随时间显示T2 *信号强度降低的像素。
T2 *信号强度随复温而降低，在七个实验中的五个实验中与颈静脉血氧饱和度降低相关。通过模糊聚类分析的T2 *成像显示CPB期间有两个弥漫分布的像素组。一大组像素（占总像素计数的50%±13%）在低温期间显示T2 *信号强度增加（组织氧合良好），复温时强度降低。第二组像素（占总像素计数的34%±8%）的变化显示T2 *信号强度逐渐降低，与温度无关，提示CPB期间脑缺氧增加。
在这个猪模型中，弥漫性空间分布的T2 *信号强度降低表明CPB期间大部分脑实质缺氧（表现为组织脱氧血红蛋白比例增加）。实质缺氧继发的神经元损伤可能解释心脏手术后的术后神经心理功能障碍。
