Cerebral Oxygeneration During Cardiopulmonary Bypass

描述(申请人提供)：脑损伤，包括局灶性和全局性 脑损伤以及次优认知发育结果仍在继续 是儿科心脏手术后的重要问题。以前在这方面的工作 该地区已将重点放在深低温停循环(DHCA)上，目前 不常使用的。作为深低温心脏停搏的替代方法 采用体外循环(CPB)。然而，在没有经过验证的 实时监测脑氧合的方法目前尚无指南 对于特定pH的CPB条件下的最小安全流量和压力， 红细胞压积和体温。 拟议的研究将采用近红外光谱分析的新技术。 (NIRS)和活体显微镜(IVM)，以确定最低安全流速 特定的灌流条件。这项研究将使用一名青少年进行 仔猪模型暴露于不同程度的流量减少，存活4 术后天数。生存状态允许评估功能证据 通过盲目兽医观察者的行为评估来评估脑损伤 以及由盲人神经病理学家确定的有意义的组织学。这些 功能和结构终点将与大脑指数相关 用组织氧合指数(TOL)、氧合血红蛋白测定氧合 最低点时间(Hb02最低点时间)以及微血管血流灌注指标 以IVM(功能毛细血管密度(FCD)、NADH荧光)测量。 拟议研究的第二阶段将对这一假设进行关键的检验 低血流灌注量减少导致脑血缺氧内皮细胞损伤 船只。这会导致内皮型一氧化氮合酶活性降低 内皮型一氧化氮合酶(ENOS)活性导致微血管局部缺血 被描述为“无回流现象”。急性研究将在#年进行。 用免疫印迹和免疫细胞化学方法建立仔猪模型 作为阻力血管造影术测定eNOS活性。ENOS活动将是 通过底物增强和抑制来操纵。诱导型一氧化氮合酶的作用 还将探讨在这种情况下引起神经毒性的一氧化氮合酶。 这项拟议的研究有可能降低脑损伤的风险 通过定义实现的安全边际来确定接受心脏手术的儿童 有不同的灌流条件。通过加强对疾病发生机制的了解 它将促进体外循环相关脑损伤的发展 新的药理学方法，进一步降低脑损伤的风险。

DESCRIPTION (Provided by Applicant): Brain damage including focal and global cerebral injury as well as suboptimal cognitive developmental outcome continue to be important problems after pediatric heart surgery. Previous work in this area has focused on deep hypothermic circulatory arrest (DHCA) which is now used infrequently. As an alternative to DHCA reduced flow hypothermic cardiopulmonary bypass (CPB) is employed. However in the absence of a validated method for real time monitoring of brain oxygenation there are no guidelines for minimal safe flow and pressure under specific CPB conditions of pH, hematocrit and temperature. The proposed study will employ the new techniques of near infrared spectroscopy (NIRS) and intravital microscopy (IVM) to defme a minimal safe flow rate for specific perfusion conditions. The study will be conducted using a juvenile piglet model exposed to various degrees of flow reduction with survival for 4 days postoperatively. Survival allows assessment of functional evidence of brain injury through behavioral assessment by a blinded veterinarian observer as well as meaningful histology determined by a blinded neuropathologist. These functional and structural endpoints will be correlated with indices of brain oxygenation measured by NIRS (Tissue Oxygenation Index (TOl), Oxyhemoglobin nadir time (Hb02 nadir time)) as well as indices of microvascular perfusion measured by IVM (functional capillary density (FCD), NADH fluorescence). The second phase of the proposed study will test the hypothesis that critically reduced low flow perfusion causes hypoxic endothelial injury of cerebral blood vessels. This results in reduced constitutive endothelial nitric oxide synthase (eNOS) activity resulting in microvascular regional ischemia previously described as the "no reflow phenomenon." Acute studies will be undertaken in the piglet model using Western immunoblotting and immunocytochemistry as well as resistance vessel myography to measure eNOS activity. eNOS activity will be manipulated by substrate enhancement and inhibition. The role of inducible NOS (iNOS) in causing neurotoxicity in this setting will also be explored. The proposed study has the potential to reduce the risk of brain injury in children undergoing heart surgery by defining the margin of safety achieved with various perfusion conditions. By enhancing understanding of mechanisms of cardiopulmonary bypass-related brain injury it will facilitate development of novel pharmacologic methods to further reduce the risk of brain damage.