The effects of regional cerebral blood flow during hyperventilation

采用非放射性彩色微球法对过度换气对兔局部脑血流的影响进行了实验研究。用氧化亚氮(67%)和氧气(33%)混合气体进行控制通气法：(1)调节通气量和通气量，使PaCO2达到30~40 mm Hg，然后向左房注入黄色微球(常碳酸组)；(2)增加通气量和通气量诱导过度换气，使PaCO_2达到25~30 mm Hg，然后向左房注入蓝色微球(低碳酸血症组)。将兔随机分为两组，一组先进行低碳酸血症，然后进行低碳酸血症；另一组先进行低碳酸血症，然后进行低碳酸血症手术。随后，分离大脑，并从脑桥、丘脑、小脑、海马体和大脑皮层的组织样本以及血液样本中提取微球以供参考。根据微球的吸收计算每个样本中的血流量，并比较正常二氧化碳和低二氧化碳过程中的血流量。低碳酸血症状态下大脑皮质和小脑的局部脑血流量显著低于正常碳酸血症状态下的局部脑血流量，但与低碳酸血症相关的海马区、桥脑区和丘脑区的血流量下降幅度较小。这些发现表明，过度换气导致的脑血流量下降在大脑皮层和小脑等需要充足氧气供应且脑血管输送血液特别多的区域尤为明显。

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.