Static Cerebral Autoregulation and Modifying factors during Moderate Hypothermia

方法：动物模型：成年Spraugue-Dawley大鼠用氟烷麻醉后进行空气/氧气呼吸，分别插管测定平均动脉压(MAP)、血气分析、输液、抽血、给药。此外，通过右侧顶骨上的一个小毛刺孔将激光多普勒探头插入靠近硬脑膜的物质中，测量局部脑血流量。在MAP(40~160 mm Hg)阶梯变化时重复测量局部脑血流量。(1)异氟醚或咪达唑仑+芬太尼麻醉时评价SCAR。(2)正常、低二氧化碳或高碳酸血症时评价SCAR。(3)常温或脑中低温(33~34℃)时评价SCAR。(4)结扎双侧颈动脉5min诱发不完全性脑缺血。结果与结论异氟醚麻醉对SCAR有明显的损伤作用，咪达唑仑+芬太尼麻醉对SCAR无明显影响。高碳酸血症对SCAR有明显的抑制作用，而低碳酸血症对SCAR有明显的调节作用。与常温相比，中度脑低温对瘢痕有明显的损伤作用。与正常大鼠相比，缺血后大鼠的SCAR明显受损。但诱导脑中低温并不会进一步加重缺血后大鼠的瘢痕形成。综上所述，在脑中低温治疗中，咪达唑仑和阿片类药物联合镇静和维持正常血压状态是可取的。尽管亚低温本身确实损害了脑的自我调节，但在脑缺血后诱导亚低温并不会导致瘢痕的进一步加重。

Methods:Animal model :After anesthetized with halothane, adult Spraugue-Dawley rats were ventilated with air/O2Femoral artery and vein were cannulated for measurement of MAP and blood gas analysis and for infusion, drawing blood, and administration of drugs, respectively. Furthermore, a probe of laser Doppler was inserted in close to dura matter through a small burr hole in the right parietal bone to measure regional cerebral blood flow. Regional cerebral blood flow was repetedly measured at stepwise change of MAP (40-160mmHg). Static cerebral autoregulation (SCAR) was assessed with % change of regional cerebral blood flow at MAP of lOOmmHg.(1) SCAR was evaluated during isoflurane or midazolam + fentanyl anesthesia.(2) SCAR was evaluated during normo, hypo, or hypercapnia.(3) SCAR was evaluated during normothermia or brain moderate hypothermia (33-34℃).(4) Incomplete brain ischemia was induced with ligation of bilateral carotid arteries for 5min. SCAR was evaluated during normothermia or brain moderate hypothermia (33-34℃) in the post-ischemic rats.Results and ConclusionsSCAR was significantly impaired during isofllurane, but not during midazolam + fentanyl anesthesia.Hypercapnia significantly impaired SCAR, in contrast, hypocapnia hyper-regulated SCAR. Moderate brain hypothermia significantly impaired SCAR as compared with normothermia.SCAR was significantly impaired in the post ischemic rats as compared with the normal rats. However, inducing brain moderate hypothermia, does not cause further aggravation of SCAR in the post ischemic rats.In summary, during brain moderate hypothermic therapy, combined sedation of midazolam and opiods and maintaining normocapnic state are preferable. Although moderate hypothermia itself does impair cerebral autoregulation, however, inducing the moderate hypothermia in the post cerebral ischemia may not cause further aggravation of SCAR.