McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, Canada.
Neuroimage. 2010 Nov 1;53(2):383-91. doi: 10.1016/j.neuroimage.2010.07.003. Epub 2010 Jul 17.
It is widely assumed in fMRI that the relationship between cerebral blood flow (CBF) and volume (CBV) changes observed during end-tidal CO(2) (PETCO(2)) perturbations is equivalent to that elicited by neuronal activation. This assumption has been validated in PET studies insofar as relating total flow to total CBV changes, but remains unconfirmed for venous CBV changes, which pertains to the primary vascular compartment modulating the BOLD signal. In this study, we measured CBF and venous CBV changes in healthy subjects in response to graded hypercapnia and hypocapnia, induced using computerized end-tidal CO(2) targeting, with a DeltaPETCO(2) range of between -6 and +9 mm Hg. Hypercapnia was found to elicit robust increases in CBF and venous CBV, while hypocapnia produced decreases in both. We used steady-state flow and volume changes to estimate the power-law relationship for cortical and subcortical brain regions, and did not observe significant difference between the two. The combined fit resulted in a power coefficient of 0.18+/-0.02, substantially lower than Grubb's coefficient of 0.38, but comparable to previous observations during neuronal activation. These results confirm that the BOLD-specific flow-volume relationship during CO(2) challenges is similar to that characterizing neuronal activation.
在 fMRI 中，人们普遍认为，在呼气末二氧化碳 (PETCO2) 波动期间观察到的脑血流 (CBF) 和体积 (CBV) 变化与神经元激活引起的变化之间存在等效关系。在 PET 研究中，这一假设已经在总流量与总 CBV 变化方面得到了验证，但对于静脉 CBV 变化尚未得到证实，静脉 CBV 变化与调节 BOLD 信号的主要血管容积有关。在这项研究中，我们使用计算机控制的呼气末 CO2 靶向技术，在健康受试者中测量了 CBF 和静脉 CBV 对逐渐性高碳酸血症和低碳酸血症的变化，DeltaPETCO2 范围在-6 至+9mmHg 之间。高碳酸血症引起 CBF 和静脉 CBV 的强烈增加，而低碳酸血症则导致两者减少。我们使用稳态流量和体积变化来估计皮质和皮质下脑区的幂律关系，并且在两者之间没有观察到显著差异。联合拟合的结果得出幂系数为 0.18+/-0.02，明显低于 Grubb 系数 0.38，但与神经元激活期间的先前观察结果相当。这些结果证实，在 CO2 挑战期间，BOLD 特异性流量-体积关系与表征神经元激活的关系相似。
