Hudetz A G, Biswal B B, Fehér G, Kampine J P
Department of Anesthesiology and Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, 53226, USA.
Microvasc Res. 1997 Jul;54(1):35-42. doi: 10.1006/mvre.1997.2023.
The velocity of red blood cells (RBC) in individual capillaries of the rat cerebral cortex was assessed using direct, intravital video microscopy under normal conditions and during systemic hypoxia or hypercapnia. The movement of RBC in capillaries within 50-microm depth of the parietal cortex was visualized with the aid of fluorescent labeling of RBC in a closed cranial window preparation in pentobarbital-anesthetized, artificially ventilated adult rats. Hypoxia was produced by lowering the concentration of oxygen in the inspired gas from 30 to 15% for 5 min. Hypercapnia was achieved by increasing the inspired CO2 concentration (FiCO2) from 0 to 5% and then to 10% for 5 min at each level. The mean arterial pressure was maintained constant during both maneuvers. Under control conditions, fast and heterogeneous RBC flow in multioriented, tortuous capillaries was observed. During hypoxia, RBC velocity increased from 0.61 +/- 0.06 to 0.82 +/- 0.10 mm/sec (35% change). During hypercapnia, RBC velocity increased from 0.73 +/- 0.05 to 1.07 +/- 0. 11 mm/sec (46% change) at 5% CO2 and to 1.19 +/- 0.11 mm/sec (63% change) at 10% CO2. Corresponding changes in regional blood flow as assessed by laser-Doppler flowmetry during hypercapnia were 69 +/- 7 and 128 +/- 21%, respectively. The RBC velocity increased in almost all capillaries during hypoxia and during moderate hypercapnia. However, a substantial number of capillaries showed no change or a small decrease in RBC velocity during severe hypercapnia. A significant negative correlation between the velocity change at 10% CO2 and the normocapnic resting velocity was found in a group of capillaries isolated by cluster analysis. These results suggest that the dominant component of cerebral hyperemic response to hypoxia and to moderate hypercapnia is an increase in capillary RBC flow velocity. A more complex change in the velocity distribution occurs during severe hypercapnia and results in increased homogeneity of RBC perfusion in the cerebrocortical capillary network.
在正常条件下以及全身缺氧或高碳酸血症期间，使用直接活体视频显微镜评估大鼠大脑皮质单个毛细血管中红细胞（RBC）的速度。在戊巴比妥麻醉、人工通气的成年大鼠的封闭颅骨窗制备中，通过对红细胞进行荧光标记，观察顶叶皮质50微米深度内毛细血管中红细胞的运动。缺氧是通过将吸入气体中的氧气浓度从30%降至15%持续5分钟来产生的。高碳酸血症是通过将吸入二氧化碳浓度（FiCO2）从0%增加到5%，然后在每个水平增加到10%持续5分钟来实现的。在这两种操作过程中，平均动脉压保持恒定。在对照条件下，观察到多方向、曲折的毛细血管中红细胞快速且不均匀地流动。在缺氧期间，红细胞速度从0.61±0.06毫米/秒增加到0.82±0.10毫米/秒（变化35%）。在高碳酸血症期间，在5%二氧化碳时红细胞速度从0.73±0.05毫米/秒增加到1.07±0.11毫米/秒（变化46%），在10%二氧化碳时增加到1.19±0.11毫米/秒（变化63%）。在高碳酸血症期间，通过激光多普勒血流仪评估的局部血流相应变化分别为69±7%和128±21%。在缺氧和中度高碳酸血症期间，几乎所有毛细血管中的红细胞速度都增加。然而，在严重高碳酸血症期间，大量毛细血管中的红细胞速度没有变化或略有下降。通过聚类分析分离出的一组毛细血管中，发现10%二氧化碳时的速度变化与正常碳酸血症静息速度之间存在显著负相关。这些结果表明，大脑对缺氧和中度高碳酸血症的充血反应的主要成分是毛细血管中红细胞流速的增加。在严重高碳酸血症期间，速度分布会发生更复杂的变化，导致大脑皮质毛细血管网络中红细胞灌注的均匀性增加。
