IEEE Trans Med Imaging. 2019 May;38(5):1295-1303. doi: 10.1109/TMI.2018.2883244. Epub 2018 Nov 26.
The cerebral vascular system provides a means to meet the constant metabolic needs of neuronal activities in the brain. Within the cerebral capillary bed, the interactions of spatial and temporal hemodynamics play a deterministic role in oxygen diffusion, however, the progression of which remains unclear. Taking the advantages of high-spatiotemporal resolution of optical coherence tomography capillary velocimetry designed with the eigen-decomposition statistical analysis, we investigated intrinsic red blood cell (RBC) velocities and their spatiotemporal adjustment within the capillaries permeating mouse cerebral cortex during electrical stimulation of contralateral hind paw. We found that the mean capillary transit velocity (mCTV) is increased and its temporal fluctuation bandwidth (TFB) is broadened within hind-paw somatosensory cortex. In addition, the degree to which the mCTV is increased negatively correlates with resting state mCTV, and the degree to which the TFB is increased negatively correlates with both the resting state mCTV and the TFB. In order to confirm the changes are due to hemodynamic regulation, we performed angiographic analyses and found that the vessel density remains almost constant, suggesting the observed functional activation does not involve recruitment of reserved capillaries. To further differentiate the contributions of the mCTV and the TFB to the spatiotemporally coupled hemodynamics, changes in the mCTV and TBF of the capillary flow were modeled and investigated through a Monte Carlo simulation. The results suggest that neural activation evokes the spatial transit time homogenization within the capillary bed, which is regulated via both the heterogeneous acceleration of RBC flow and the heterogeneous increase of temporal RBC fluctuation, ensuring sufficient oxygenation during functional hyperemia.
脑血管系统为大脑神经元活动的持续代谢需求提供了一种途径。在脑毛细血管床内，时空血液动力学的相互作用对氧扩散起着决定性的作用，但进展尚不清楚。利用基于特征分解统计分析设计的具有高时空分辨率的光相干断层扫描毛细血管速度测量法，我们研究了在对侧后爪电刺激期间，穿过小鼠大脑皮层的毛细血管内固有红细胞（RBC）速度及其时空调整。我们发现，在后爪感觉皮层内，平均毛细血管转运速度（mCTV）增加，其时间波动带宽（TFB）变宽。此外，mCTV 增加的程度与静息状态 mCTV 呈负相关，TFB 增加的程度与静息状态 mCTV 和 TFB 均呈负相关。为了确认这些变化是由于血液动力学调节引起的，我们进行了血管造影分析，发现血管密度几乎保持不变，这表明观察到的功能激活不涉及储备毛细血管的募集。为了进一步区分 mCTV 和 TFB 对时空偶联血液动力学的贡献，我们通过蒙特卡罗模拟对毛细血管流动的 mCTV 和 TFB 变化进行了建模和研究。结果表明，神经激活引起毛细血管床内空间转运时间的均匀化，这是通过 RBC 流动的异质性加速和 RBC 时间波动的异质性增加来调节的，从而确保在功能充血期间有足够的氧合。
