Possible control of intermittent cerebral ischemia by monitoring of direct-current potentials

Object. Neurosurgically induced temporary occlusion of intracranial arterie s carries the risk of cerebral ischemic damage. Because negative shifts in the cortical direct-current (DC) potential indicate tissue depolarization a nd, thus, critical ischemic stress, the authors hypothesized that recording s of these potentials could help to determine the optimal duration and freq uency of induced intermittent focal ischemia to prevent brain injury. The i nvestigators related the results of DC recordings both to simultaneously re corded decreases in extracellular Ca++ concentration ([Ca++](o)), which ref lect Ca++ entry into cells, and to histological outcome. Methods. In cats anesthetized with halothane the effects of intermittent br ief (10 minutes long, six times [6 x 10-min group]) and prolonged (20 minut es long, three times [3 x 20-min group]) episodes of middle cerebral artery occlusions were compared with those of a single continuous episode (1 x 60 -min group). Laser Doppler flow probes and ion-selective microelectrodes we re used to measure cerebral blood flow, DC potentials, and [Ca++](o) in cor tical tissues of ectosylvian gyri. Negative shifts in DC potential were evaluated in the three groups during t he entire 60-minute-long period of ischemia and were smallest in the 6 x 10 -min group, larger in the 3 x 20-min group, and largest in the 1 x 60-min g roup. Accordingly, infarct volumes were smallest in the 6 x 10-min group, i ntermediate in the 3 x 20-min group, and largest in the 1 x 60-min group. D ecreases in ischemic [Ca++](o) were significantly greater in the 1 x 60-min group than in the two groups in which there were repetitive occlusions, an d recovery of [Ca++], after reperfusion normalized only in the 1 x 60-min g roup. Conclusions. The DC potential may provide a reliable measure to optimize in termittent ischemia and to achieve minimal ischemic brain injury during tem porary neurosurgical occlusion of cerebral arteries.