Recovery of the electrocorticogram after incomplete and complete ischaemia of the brain.

Incomplete cerebral ischaemia of 10 to 60 minutes duration was performed by reducing the perfusion pressure of completely isolated canine heads at brain temperatures of 37 and 32 degrees C. Complete cerebral ischaemia of the same duration was performed by complete stopping of the perfusion. The latency of recovery of the electrocorticogram, i.e. the time interval from the end of the cerebral ischaemia until reappearance of the first spontaneous cortical potentials, was shorter after incomplete ischaemia than after complete ischaemia. At 37 degrees C brain temperature the latency of recovery of the electrocorticogram was zero after a perfusion of the brain with a perfusion pressure of 22 mm Hg for 1 hour. After an incomplete ischaemia of 1 hour produced by a perfusion pressure of 20 mm Hg the latency of recovery was 0 to 4 minutes. Lower perfusion pressures increased the latency of recovery considerably. Reduction of brain temperature to 32 degrees C decreased the latency of recovery. At perfusion pressures of 22 mm or more there was no difference in the latency of recovery between 37 and 32 degrees C brain temperature.