Mizoi K, Suzuki J, Abiko H, Ogasawara K, Oba M, Yoshimoto T
Division of Neurosurgery, Tohoku University School of Medicine, Sendai, Japan.
Acta Neurochir (Wien). 1987;88(3-4):126-34. doi: 10.1007/BF01404149.
The flow threshold and time threshold for reversibility of cerebral ischemia were studied using a canine model of cerebral ischemia regulated by controlled perfusion of cerebral blood flow (CBF). CBF was continuously monitored with a laser Doppler flow meter, the brain was brought to a constant level of ischemia for a defined period of time, after which recirculation was instituted. The electroencephalogram (EEG) and somatosensory evoked potentials (SEP) were monitored and used as an index of brain function. No recovery of brain function was found following recirculation if the CBF was reduced to a level below 20% of the normal state for more than one hour. When residual blood flow was 30% of the normal level, however, recirculation after one hour of ischemia resulted in nearly complete recovery of brain function. Significant functional recovery was not seen after two or more hours of such ischemia. Nearly complete recovery was also seen following reperfusion within three hours with 40% of normal CBF. It was demonstrated that the reversibility in the ischemic brain was critically correlated to the level of blood flow and its duration. If these results can be applied to the human brain, emergency cerebral revascularization for ischemic stroke should be attempted when critical flow and time thresholds have not been crossed, namely, in less than 1 hour and 3 hours of insult when the residual blood flow is reduced to 30 and 40% of the normal state, respectively. In clinical situations, this "critical time" may be too short for acute revascularization unless cerebral protective measures are applied pre-operatively to prolong the viability period of ischemic cerebral tissue.
利用通过控制脑血流量（CBF）灌注来调节的犬脑缺血模型，研究了脑缺血可逆性的流量阈值和时间阈值。用激光多普勒流量计持续监测CBF，使大脑在规定时间内达到恒定的缺血水平，之后再进行再灌注。监测脑电图（EEG）和体感诱发电位（SEP），并将其用作脑功能指标。如果CBF降低到正常状态的20%以下并持续超过1小时，再灌注后未发现脑功能恢复。然而，当残余血流量为正常水平的30%时，缺血1小时后再灌注导致脑功能几乎完全恢复。缺血两小时或更长时间后未观察到明显的功能恢复。在正常CBF的40%下三小时内再灌注后也观察到几乎完全恢复。结果表明，缺血性脑的可逆性与血流量水平及其持续时间密切相关。如果这些结果可应用于人类大脑，对于缺血性中风，当未超过临界流量和时间阈值时，即分别在损伤后不到1小时和3小时且残余血流量分别降至正常状态的30%和40%时，应尝试进行紧急脑血运重建。在临床情况下，除非术前采取脑保护措施以延长缺血性脑组织的存活期，否则这个“临界时间”对于急性血运重建可能太短。
