VARIATIONS IN FLOW DYNAMICS IN CEREBRAL CAPILLARY BEDS

局部脑血流量（LCBF）的变化率为6倍， 在清醒状态下的中枢神经系统结构中更多。 可能的 LCBF差异和改变的原因包括 每单位组织灌注毛细血管体积的差异 血液流动的线速度的变化 毛细血管 我们建议调查这些变化， 在对照和LCBF改变条件下大鼠的LCBF， 假设：1）LCBF中的这些差异主要是 灌注毛细血管局部体积差异的结果; 2)局部毛细血管内灌注毛细血管的百分比 床通常在CNS结构之间变化， 当LCBF改变时改变;和3）LCBF的调制 包括增加（“招聘”）和减少（“退休”） 当LCBF为中等时，灌注毛细血管的百分比 改变，但不仅涉及毛细血管的招聘退休， 也改变了毛细血管内血液的线性流速， LCBF明显改变。 为了验证这些假设，LCBF将 在四组实验中， 到不同O2和CO2含量的气体混合物中， 戊巴比妥麻醉 以下参数 在对照大鼠和五个实验组中测量， 放射性示踪剂分布技术，定量放射自显影， 图像分析和光学显微形态测量：1）LCBF，2） 局部脑葡萄糖利用率; 3）局部灌注体积 微血管（灌注的“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）平均局部毛细血管长度; 7）平均线性 毛细血管内血流速度（线流速）; 8）局部 毛细血管体积和9）灌注的毛细血管的百分比。“若 LCBF的变化主要是由于当地 灌注毛细血管的体积（第一个假设），然后有 应该是我们的实验 LCBF和灌注“毛细血管”体积的测定值，以及 我们估计的LCBF和局部血脑 传递常数是灌注毛细血管的函数， 表面积;此外，线性流速应类似于 所有大脑区域。 如果改变LCBF会改变 灌注毛细血管（第二个假设），然后百分比 从我们的数据中评估的灌注“毛细血管”应该转移到 与LCBF的变化同步。 LCBF变化的比较 随着灌注的“毛细血管”体积的变化， 速度和灌注的“毛细血管”的百分比将指示 这些不同血流模式中的每一种的相对重要性 在LCBF的小和大的变化，并提供我们的测试 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.