The effects of regional cerebral blood flow during hyperventilation

采用非放射性彩色微球法对家兔局部脑血流变化进行了评价。兔采用氧化亚氮（67%）和氧气（33%）混合控制通气，进行以下操作：(1)通过调节通气频率和潮气量获得30 ~ 40 mmHg的PaCO_2，左心房注射黄色微球（常氧组）；(2)通过增加换气频率和潮气量诱导换气过度，使PaCO_2达到25 ~ 30 mmHg，左心房注射蓝色微球（低碳酸血症组）。将家兔随机分为两组，一组先进行低碳酸血症再进行正常碳酸血症处理，另一组先进行正常碳酸血症再进行低碳酸血症处理。按照程序，分离大脑，从脑桥、丘脑、小脑、海马和大脑皮层的组织样本以及血液样本中提取微球作为参考。在微球吸收的基础上计算每个样品的血流量，并比较正常碳酸盐岩和低碳酸盐岩的血流量。低碳酸血症状态下大脑皮层和小脑的局部脑血流量明显低于正常碳酸血症状态，但低碳酸血症相关的海马、桥脑桥和丘脑的血流量减少幅度较小。这些发现表明，过度通气导致的脑血流量减少在大脑皮层和小脑等区域尤为显著，这些区域需要充足的氧气供应，并且脑血管的血液输送量特别大。

An experimental study using the non-radioactive colored microsphere method was conducted to evaluate changes in regional cerebral blood flow associated with hyperventilation in rabbits. Rabbits underwent controlled ventilation using a mixture of nitrous oxide (67%) and oxygen (33%), and were subjected to the following procedures : (1)PaCO_2 of 30-40 mmHg was obtained by adjusting ventilation frequency and tidal volume and yellow microspheres were then injected into the left atrium (normocapnia group) ; and (2)hyperventilation was induced by increasing ventilation frequency and tidal volume to achieve a PaCO_2 of 25-30 mmHg and blue microspheres were then injected into the left atrium (hypocapnia group). Rabbits were randomly allocated to two groups, one undergoing first the hypocapnia and then the normocapnia procedure and the other undergoing first the normocapnia and then the hypocapnia procedure. Following the procedures, the brain was isolated and microspheres were retrieved from tissue samples from the pons, thalamus, cerebellum, hippocampus, and cerebral cortex as well as blood samples for reference. Blood flow in each sample was calculated on the basis of absorption of microspheres, and comparison of blood flow between normocapnic and hypocapnic procedures was performed. Regional cerebral blood flow in the state of hypocapnia was significantly lower in the cerebral cortex and cerebellum than in the state of normocapnia, but the magnitude of hypocapnia-associated decrease in blood flow was small in the hippocampus, pons, and thalamus. These findings indicate that the decrease in cerebral blood flow due to hyperventilation is especially significant in areas such as the cerebral cortex and cerebellum that require abundant supply of oxygen and to which delivery of blood from cerebral vessels is especially large.