VARIATIONS IN FLOW DYNAMICS IN CEREBRAL CAPILLARY BEDS

局部脑血流量(LCBF)的变化是6倍或 更多处于清醒状态的中枢神经系统结构。可能的 导致LCBF不同和变化的原因包括 单位组织内微血管灌流体积的差异 内血流的体积和线速度的变化 毛细血管。我们建议在以下方面调查这些变化 对照组和LCBF改变条件下大鼠的下丘脑血流量 假设：1)LCBF的这些差异主要是 局部灌注毛细血管体积不同所致； 2)局部毛细血管内灌流的毛细血管百分比 在不同的中枢神经系统构造中，床层通常不同，这个百分比 LCBF改变时的变化；3)LCBF的调制 涉及增加(招聘)和减少(退休) LCBF为中度时的毛细血管灌注率 但不仅涉及毛细招募-退休，而且 毛细血管内血流线速度的变化 下丘脑血流量明显改变。为了检验这些假设，LCBF将 通过暴露四组实验率来改变它们 到不同含量的02和C02的气体混合物和一组 由戊巴比妥麻醉。以下参数将是 在对照组和五个实验组中进行测量，使用 放射性示踪剂分配技术，定量放射自显影， 图像分析和光学显微形态计量学：1)LCBF，2) 局部脑葡萄糖利用；3)局部灌注量 微血管(灌流的“毛细血管”体积)；4)局部血脑 四种化合物的传递常数；5)平均局部毛细管 通过时间；6)平均局部毛细管长度；7)平均线性 毛细血管内血流速度(线血流速度)；8)局部 毛细血管体积和灌流的“毛细血管”百分比。如果 LCBF的变化主要是由于局部的差异。 灌流的毛细血管体积(首先是假设)，然后是 在我们的实验中应该是密切相关的 测定LCBF和灌流“毛细血管”容量，以及 我们对LCBF的估计和当地的血脑也是一样的 传递常数，这是灌流毛细管的函数 表面积；此外，线流速应与 所有的大脑区域。如果更改LCBF会改变 灌流的毛细血管(第二个假设)，然后 根据我们的数据评估的灌流的“毛细血管”应该会转移到 与LCBF变化平行。LCBF变化的对比研究 随着“毛细血管”灌注量的变化， 血流速度和灌流“毛细血管”的百分比将表明 这些不同血流模式中每一种的相对重要性 在LCBF中有小有大的变化，并提供我们的 第三个假设。

The rate of local cerebral blood flow (LCBF) varies six-fold or more among CNS structures in the awake conditions. The possible causes of the dissimilarities and alterations in LCBF include differences in the volume of perfused capillaries per unit tissue volume and variations in the linear velocity of blood flow within the capillaries. We propose to investigate these variations in LCBF in rats under contol and LCBF altering conditions and hypothesize that: 1) these dissimilarities in LCBF are mainly the result of differences in the local volumes of perfused capillaries; 2) the percentage of perfused capillaries within local capillary beds normally varies among CNS structures and this percentage changes when LCBF is altered; and 3) the modulation of LCBF involves increasing ("recruiting") and decreasing ("retiring") the percentage of perfused capillaries when LCBF is moderately altered but involves not only capillary recruitment-retirement but also changes in linear flow velocity of intracapillary blood when LCBF is markedly altered. To test these hypotheses, LCBF will be altered in four groups of experimental rates by exposing them to gas mixtures of varying 02 and C02 contentt and in one group by pentobarbital anesthesia. The following parameters will be measured in control rats and the five experimental groups using radiotracer distribution techniques, quantitative autoradiography, image analysis and light micrographic morphometry: 1) LCBF, 2) local cerebral glucose utilization; 3) local volumes of perfused microvessels (perfused "capillary" volume); 4) local blood-brain transfer constants of four compounds; 5) mean local capillary transit time; 6) mean local capillary length; 7) mean linear velocity of intracapillary blood flow (linear flow velocity); 8) local capillary volume, and 9) percentage of perfused "capillaries." If the variations in LCBF are mainly due to differences in the local volume of perfused capillaries (first hypotheses), then there should be a close correlation between our experimentally determined values of LCBF and perfused "capillary" volume, and also between our estimates of LCBF and local blood-brain transfer constants, which are functions of perfused capillary surface area; moreover linear flow velocity should be similar in all brain areas. If changing LCBF alters the percentage of perfused capillaries (second hypotheses), then the percentages of perfused "capillaries" assessed from our data should shift in parallel with LCBF changes. Comparisons of the changes in LCBF with the variations in perfused "capillary" volume, linear flow velocity, and percentage of perfused "capillaries" will indicate the relative importance of each of these modes of varying blood flow with small and large shifts in LCBF and provide the testing of our third hypothesis.