Analysis of Blood Flow Dynamics in Cerebral Microvessels by a fiber-Optic Laser-Doppler Anemometer Microscope

本研究项目旨在利用我们研制的光纤激光多普勒风速显微镜（FLDAM）分析不同病理条件下的血流动力学。特别地，我们研究了颅内压升高对脑脊膜动脉网络脉冲波传播的影响以及一氧化氮对脑脊膜微血管流速分布的影响。在大鼠顶骨区建立封闭的颅窗，观察大鼠颅底微循环。用FLDAM测定单头微血管内红细胞流速。窗内压（等于颅内压）在0 ~ 50mmhg之间变化。小动脉红细胞流速与股动脉体表动脉压同步显示有规律的脉动波形。以系统压力作为定时信号，将速度脉动的幅度定义为总体平均水平最大值与最小值之差的一半。动脉小动脉流速脉动幅值为24 (]SY.+-。[) 9%, 29(] .+-。[) 9%和40 (]SY.+-。[]在ICP = 5、30和50 mmHg时，分别有11%。随着ICP的平均升高，其逐渐升高。然而，在个别小动脉中，在一定的ICP临界值时，速度脉动幅度急剧增加。临界ICP范围在25 ~ 40 mmHg之间，随血管直径的增加而增加，沿小动脉树从上游到下游逐渐降低。假设小动脉壁弹性模量是跨壁压力的阶跃函数，网络结构近似为多孔锥形弹性管，在此基础上进行了理论计算。他们认为临界ICP对应于小动脉的内部压力。恒定剪切应力假说被引入来解释小动脉体积流量与血管直径的立方关系。该假说的机制是基于一氧化氮（NO）介导的血流依赖性血管扩张。然而，我们通过FLDAM的测量显示，大鼠头动脉的流速与3.46 (]SY.+-成正比。[) 0.18<@D2-@>直径的d2次幂，与3有显著差异。为了研究一氧化氮对流速分布的影响，我们在输注硝托russide钠（SNP，一种有效的一氧化氮供体）的情况下，测量了直径在20 ~ 60 μ m之间的心肌小动脉的红细胞流速。直径和平均速度平均增加14%。与控制条件相比，平均速度和壁面剪切速率的分布没有明显变化。少

This research projecto was aimed to analyze the blood flow dynamics undr the various pathological conditions using our developed fiber-optic laser-Doppler anemometer microscope (FLDAM). In particular, effects of incresed intracranial pressure on the pulse wave propagation along the pial arteriolar network and effects of nitric oxide on the velocity distributions in the pial microvessels were studied.To observe the brain pial microcirculation, a closed cranial window was created on the parietal region of the rats. The red cell velocity in single pial microvessels was measured by the FLDAM.The internal pressure of the window, which is equal to the intracranial pressure, was changed between 0 and 50 mmHg. The red cell velocity in arterioles showed regular pulsatile waveforms synchronous with the systemic arterial pressure measured in the femoral artery. The amplitude of velocity pulsation was defined as the half of the difference between the maximum and minimum of the ensemble average vel … More ocity using the systemic pressure as a timing signal. The amplitude of velocity pulsation in the pial arterioles was 24 (]SY.+-。[) 9%, 29 (]SY.+-。[) 9% and 40 (]SY.+-。[) 11% at ICP = 5,30 and 50 mmHg, respectively. It increased gradually with ICP on the average. In individual arterioles, however, the amplitude of velocity pulsation showed a sharp increase at a certain critical value of ICP.The critical ICP ranged between 25 and 40 mmHg, increased with increasing vessel diameter and decreased from upstream to downstream along arteriolar trees. Theoretical calculations wereconducted based on a model assuming that the elastic modulus of arteriolar wall is a step function of transmural pressure and the network architecture is approximated by a porous tapered elastic tube. They suggest that the critical ICP corresponds to the internal pressure of the arteriole.Constant shear stress hypothesis has been introduced to explain the cubic dependence of the volumetric flow in arterioles on vessel diameter. The mechanism of the hypothesis is based on the flow dependent vasodilation mediated by nitric oxide (NO). However, our measurements by the FLDAM revealed that the flow rate in the rat pial arterioles is proportional to the 3.46 (]SY.+-。[) 0.18<@D2-@>D2th power of the diameter, which is significantly different from 3. To investigate the effects of NO on the velocity distribution, the red cell velocity was measured in the pial arterioles with diameter between 20 and 60 mum under the infusion of sodium nitoprusside (SNP,a potent NO donor). Both diamete and mean velocity increased by 14% on the average. The distributions of mean velocity and wall shear rate did not show significant changes compared to the control condition. Less