Cerebral Microvascular Hemodynamics and its Regulation Studied by a Laser-Doppler Method

本研究旨在利用自制的光纤激光多普勒风速显微镜（FLDAM）分析脑微循环血流动力学及其调控。FLDAM测量单个微血管的横截面平均速度，具有较高的时间和空间分辨率。它工作在反向散射模式下，光源强，适合于大脑等固体器官的表面微循环。在本研究中，FLDAM的时间分辨率进一步提高到1ms，速度范围限制为200mm /s，从而可以测量直径大于100 μm的动脉小动脉的脉动速度。实际上，在沙鼠全脑缺血再灌注时，通过阻断双侧颈总动脉，测量了沙鼠头部小动脉速度的时间变化，证实了这一点。血流速度在血管最大收缩期先降至0左右，再灌注后血流速度约为对照速度的两倍（约10 mm/s）。采用FLDAM研究了一氧化氮（NO）（l -精氨酸摄入）对卒中易发自发性高血压大鼠大脑微循环的影响。4 ~ 12周龄，对照组大鼠直径大于20 μm的心肌小动脉直径、平均血流速度和壁剪切率显著下降，而l -精氨酸组大鼠心肌小动脉直径、平均血流速度和壁剪切率下降幅度较小。4 ~ 12周，对照组血浆NO浓度也显著下降，而l -精氨酸组下降幅度较小。由于光学相干断层扫描（OCT）可以测量2-3毫米深度的高散射介质的内部结构，空间分辨率约为10 μm，因此开发了OCT显微镜系统，用于大脑皮层微血管和神经网络的体内三维成像。对大鼠肠系膜制剂中微血管的体外观察证实了其成像能力。空间分辨率为14 μm（横向）× 16 μm（纵向），成像深度大于600 μm。少

This research project was aimed to analyze the blood flow dynamics and its regulation of cerebral microcirculation using our developed fiber-optic laser-Doppler anemometer microscope (FLDAM). The FLDAM measures the cross-sectional mean velocity in a single microvessel with high temporal and spatial resolutions. It is suitable for surface microcirculation of solid organs like brain, because it operates under a back scatter mode and the light source is intense.In this study, the FLDAM has been further improved in its temporal resolution up to 1 ms and in the limits of velocity range up to 200 mm/s, so that it can measure pulsatile velocity in the pial arterioles with diameter larger than 100 μm. Actually, they were confirmed by measuring the temporal changes of velocity in the gerbil pial arterioles during a whole brain ischemia-reperfusion by occluding the bilateral common carotid arteries. The velocity first decreased to about 0 during the period of maximal vasoconstriction and then in … More creased to about double the control velocity (a few 10 mm/s) after reperfusion.Effects of nitric oxide (NO)(L-arginine intake) on the cerebral microcirculation in stroke-prone spontaneously hypertensive rats were investigated by the FLDAM.The diameter, mean blood velocity and wall shear rate in the pial arterioles with diameter larger than 20 μm decreased significantly from 4 to 12 weeks of age for the control group, while they decreased less significantly for the L-arginine group. Plasma NO concentration also decreased significantly from 4 to 12 weeks for the control group, while the decrease was less significant for the L-arginine group.Since the optical coherence tomography (OCT) can measure the internal structure of highly scattering medium to 2-3 millimeters in depth with a spatial resolution about 10 μm, OCT microscope system was developed for the purpose of in vivo 3-dimensional imaging of microvascular as well as neural networks in the cerebral cortex. The in vitro observation of microvessels in the rat mesentery preparation demonstrated its imaging capability. The spatial resolution was found to be 14 μm (lateral) by 16 μm (longitudinal) and the imaging depth was larger than 600 μm. Less