Static Cerebral Autoregulation and Modifying factors during Moderate Hypothermia

方法：动物模型：成年SD大鼠氟烷麻醉后，空气/氧气通气，股动脉插管，测定MAP，血气分析，输液，抽血，给药。此外，通过右侧顶骨上的小钻孔将激光多普勒探头插入硬脑膜附近以测量局部脑血流量。在MAP逐步变化（40- 160 mmHg）时重复测定局部脑血流量。静态脑自动调节（SCAR）用MAP为100 mmHg时局部脑血流量的%变化来评估。(1)在异氟醚或咪达唑仑+芬太尼麻醉期间评价SCAR。(2)在正常、低或高碳酸血症期间评价SCAR。(3)在正常体温或脑部中度低温（33-34℃）期间评估SCAR。(4)结扎双侧颈总动脉5 min造成不完全性脑缺血。结果与结论异氟烷麻醉可明显抑制SCAR，而咪达唑仑+芬太尼麻醉对SCAR无明显影响，高碳酸血症可明显抑制SCAR，而低碳酸血症可明显抑制SCAR。与常温组相比，中度脑低温可明显降低SCAR，与正常组相比，脑缺血后大鼠的SCAR明显降低。结论：脑亚低温治疗中，咪唑安定与阿片类药物联合镇静，维持正常碳酸血症状态是较好的治疗方法。虽然亚低温本身会损害脑自身调节功能，但在脑缺血后诱导亚低温可能不会进一步加重SCAR。

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.