Measurement of Blood Flow Velocity in Cerebral Microvessels by a Fiber-Optic Laser-Doppler Anemometer Microscope

本研究旨在探讨自行研制的光纤激光多谱勒测速显微镜(FLDAM)在测量脑软脑膜微血管中红细胞速度的适用性，并分析颅内压升高时的血流动力学。在大鼠一侧顶区植入闭合颅窗，观察脑软脑膜微循环。用FLDAM成功地测量了单个软脑膜微血管的红细胞速度，其直径在10~230微米之间，小动脉的红细胞速度与心脏搏动同步，其幅度高达平均速度的46%，而小静脉的速度仅表现为小幅度的随机波动。速度脉动的幅度定义为集合平均速度的最大值和最小值之差的一半。小动脉内的平均血流速度随…的增加而增加更大的直径。平均直径为10微米和50微米的微动脉的平均血流速度分别为3.50 mm/S和3.50 mm/min。微动脉内血流速度相对于股动脉压的时间滞后随血管从上游向下游的距离增加而增大，表明血流脉冲沿微动脉传播。测定了几条软脑膜小动脉的血流脉冲传播速度。通过改变植入大鼠闭合颅窗的内压，研究了颅内压对软脑膜微循环的影响。当颅内压从0增加到50 mm Hg时，小静脉的平均直径从1.1单调减小到0.78，其中直径以5 mm Hg时的直径归一化。小静脉的平均血流速度从0.85单调增加到1.91。结果表明，ICP对小静脉流量的影响不明显，但与小静脉相比，小动脉的变化较小。在一定的ICP值、ICPlt；cr‘和Gt；时，微动脉的速度脉动幅度随ICP值的增大而递增，且与血管的位置有关。ICPlt；cr&gt；随血管直径增大而增大，沿小动脉从上游向下游递减，提示ICPlt；cr&gt；代表微动脉在某一搏动时相的血管内压。较少

This research project was aimed to establish the applicability of our developed fiber-optic laser-Doppler anemometer microscope (FLDAM) to the measurement of red cell velocity in the cerebral pial microvessels and was also aimed to analyze the blood flow dynamics under the increased intracranial pressures.A closed cranial window was implanted on one side of the parietal region of rats to observe the brain pial microcirculation. The red cell velocity in single pial microvessels with diameter range from 10 to 230 mum was successfully measured by the FLDAM.The red cell velocity in arterioles showed regular pulsation synchronous with the heart beats with amplitude up to 46 % of the mean velocity, while the velocity in venules only showed random fluctuations with small amplitude. The amplitude of velocity pulsation was defined as the half of the difference betweenthe maximum and minimum of the ensemble average velocity. The temporal mean velocity in the arterioles increased with increasing … More diameter. It was 3.5 and 14 mm/s for the arteriole with 10 and 50 mum in diameter, respectively, on an average. The time lag of the velocity in the arteriole relative to the femoral arterial pressure increased with the distance along the vessel from upstream to downstream, which indicates the propagation of flow pulse along the arteriole. The propagation velocity of flow pulse was determined for several pial arterioles. It ranged between 10 and 115 cm/s.Effects of intracranial pressure (ICP) on the pial microcirculation were studied by changing the internal pressure of the closed cranial window implanted in the rats. The average diameter of venules decreased monotonically from 1.1 to 0.78 as the ICP increased from 0 to 50 mmHg, where the diameter is normalized by the diameter at ICP=5mmHg. On the other hand, the temporal mean velocity in venules increased monotonically from 0.85 to 1.91. As a result, the volume flow rate in venules did not change significantly with ICP.The changes of arterioles with ICP were small compared with those of venules. The amplitude of velocity pulsation in arterioles showed stepwise increase with ICP at a certain value of ICP,ICP_<cr'> which depended on the location of the vessel. ICP_<cr> increased with increasing vessel diameter and decreased from upstream to downstream along an arteriole, suggesting that ICP_<cr> represents the intravascular pressure of the arteriole at a certain phase of pulsation. Less