CT灌注评价高碳酸血症模型下正常大鼠脑组织血流动力学变化

目的探讨CT灌注评价高碳酸血症模型下正常大鼠脑组织血流动力学变化的可行性;研究大鼠CT灌注参数变化率与α-SMA表达之间的相关性。方法 10只雄性SD大鼠,体质量250～300g,在吸入空气和吸入高浓度CO2混合气体(10%CO2和90%空气组成)后15min,分别使用GE16层Light Speed CT扫描仪对大鼠脑尾状核层面进行CT灌注扫描,原始图像经GE ADW4.2工作站Perfusion3.0脑部灌注软件处理后产生灌注曲线及伪彩图像,两次扫描前均测定大鼠的血液CO2分压、pH值等血气分析指标。检查结束后24h内,大鼠取脑固定,在尾状核中心层面切片,进行脑组织HE染色及鼠特异性SMA抗体免疫组化染色。应用SPSS11.5统计学软件进行分析:采用配对t检验,比较正常大鼠右侧尾状核在吸入空气和吸入高浓度CO2混合气体后CT灌注参数脑血容量(CBV)、脑血流量(CBF)、血管表面通透性(PS)和平均透过时间(MTT)的变化有无差异;采用Pearson相关分析分别检测大鼠右侧尾状核的SMA阳性血管染色计数与灌注参数CBV和CBF在CO2分压升高前后的变化率相关性。结果所有大鼠在吸入含10%CO2和90%空气的混合气体15min后,动脉血CO2分压均明显升高(t=9.39,P0.001),血浆pH值降低(t=13.49,P0.001)。正常SD大鼠右侧基底节区CBV、CBF、PS每100g组织分别为(10.28±4.01)mL、(304.95±88.77)mL/min、(0.26±0.37)mL/min,MTT值为(1.48±0.07)s;吸入10%CO2和90%空气的混合气体后右侧基底节区CBV、CBF值明显增加,每100g组织分别为(19.25±8.42)mL(t=4.92,P=0.001)和(507.33±167.94)mL/min(t=6.75,P0.001);吸入混合气体前后CBV、CBF增加百分比分别为(87.14±46.45)%、(65.75±22.05)%;PS及MTT变化不显著(P均0.05)。大鼠脑组织α-SMA阳性染色血管计数为(12.7±3.23)条/高倍视野。Pearson相关分析显示,正常脑组织的CBV和CBF变化率与其α-SMA阳性计数之间呈显著相关(r分别为0.652和0.890,P均0.05)。结论 CT灌注技术在改变血液CO2分压的条件下可以反映脑组织血流动力学变化;大鼠正常脑组织高碳酸血症前后CT灌注参数变化率与成熟血管数量相关。

Functional Response to Hypercarbia in Normal Rat Brain Studied by Perfusion CT

Objective To investigate the changes of CT perfusion values in normal rat brain tissue at hypercarbia and analyze the correlation between perfusion CT and the results of α-SMA immunohistochemical analysis.Methods A total of 10 male SD rats,weighting 250-300 g were used in this study.Perfusion CT was performed pre-and post-inhalation （15 minutes delay） of a mixture of 10% CO2 and 90% air.Perfusion CT values （CBV,CBF,PS and MTT） were meas-ured at the right nucleus caudatus in the rat brain.The rats were killed and their brains were removed within 24 hours after perfusion CT.Tissue samples of the nucleus caudatus in the rat brain were examined by histology using HE and immunohistochemical staining for α-SMA.Paired t test was used to determine the differences in perfusion CT values at the right nucleus caudatus in normal rat brain pre-and post-hypercarbia.The differences in the changing rate （%） of CBV,CBF,PS and MTT between the right and the left caudate nucleus of rats inhaled 10% CO2 mixture gas were determined using paried t test.Pearson correlation coefficients were used to assess the relationship between number of SMA positively stained vessels and changing rate （%） of CBV and CBF at right nucleus caudatus in the normal rat brain tissues.Results The CBV,CBF,PS and MTT values （mean ± SD） of normal rat right caudate nucleus area were （10.28 ± 4.01） mL /100 g,（304.95 ± 88.77） mL/min.100 g,（0.26 ± 0.37） mL/min.100 g,and （1.48 ± 0.07） s,respectively.After inhalation of a mixture of 10% CO2 and 90% air,the CBV and CBF values of the right caudate nucleus area were significantly higher than those before hypercarbia （t=4.92,P=0.001 and t=6.75,P0.001）.The increasing rates of CBV and CBF were （87.14 ± 46.45）% and （65.75 ± 22.05）%,respectively.However,no significant differences were detected for changes of PS and MTT after hypercarbia （P0.05 for both）.The changs of CBV,CBF,PS and MTT of right caudate nucleus area were not significant compared with those of the contralateral brain tissues （P0.05 for all）.Immunohistochemical staining of normal SD rat brain tissues for SMA was all positively expressed in the smooth muscles of blood vessels,presenting as brown regular loops or tubes.The number for SMA positively stained vessels （mean ± SD） were 12.7 vessels per field ± 3.23.Significant correlations were observed between the number for SMA positively stained vessels and changing rates of CBV and CBF after hypercarbia in rat normal brain tissues （r=0.652 and r=0.89,respectively;P0.05 for both）.Conclusions Perfusion CT in the change in blood PaCO2 can reflect the hemodynamic changes in normal rat brain tissues.These results demonstrate that changing rates of CBV and CBF correlate well with the number of mature vessels by means of changing blood PaCO2 in normal rat brain tissues.