Static Cerebral Autoregulation and Modifying factors during Moderate Hypothermia

方法：动物模型：成年sprague - dawley大鼠经氟烷麻醉后，采用空气/ o2通气，分别插管股动脉和股静脉进行MAP测定和血气分析，并进行输注、抽血和给药。此外，激光多普勒探头通过右顶骨的小钻孔插入硬脑膜附近，测量区域脑血流量。在MAP （40 ~ 160mmhg）逐步变化时反复测量脑区域血流量。静态脑自动调节（SCAR）以lOOmmHg MAP区域脑血流量变化百分比评估。(1)评估异氟醚或咪达唑仑+芬太尼麻醉时的SCAR。(2)在正常、低或高碳酸血症时评估SCAR。(3)在常温或脑中低温（33-34℃）时评估SCAR。(4)结扎双侧颈动脉5min诱导不完全脑缺血。评估缺血后大鼠在常温或脑中低温（33-34℃）时的SCAR。结果与结论异氟醚麻醉对scar有明显损害，咪达唑仑+芬太尼麻醉对scar无明显损害。高碳酸血症显著损害SCAR，相反，低碳酸血症过度调节SCAR。与常温相比，中度脑低温显著损害了SCAR。与正常大鼠相比，缺血后大鼠的SCAR明显受损。然而，诱导脑中低温并不会导致缺血后大鼠SCAR的进一步加重。综上所述，在脑中低温治疗过程中，咪达唑仑和阿片类药物联合镇静，维持正常状态是优选的。虽然中低温本身确实会损害大脑的自调节功能，但在脑缺血后诱导中低温可能不会导致SCAR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.