Frequency changes of sensorimotor EEG rhythm after revascularization surgery.

In a group of 26 patients undergoing extra-intracranial arterial bypass surgery (EIAB), the frequency of sensorimotor rhythms was measured shortly before and 7 days after EIAB surgery. Bipolar EEG recording from both central regions was used for calculation of power spectra and measurement of peak frequency to determine the dominant frequency of the sensorimotor rhythm. Preoperative hemispheric comparisons displayed a statistically significant frequency decrease (-0.47 Hz) on the ischaemic side, only in the group (15 patients) with cortical infarction. The hand pressure, measured electronically, showed a tendency to decrease in the early postoperative stage. Measurement of the frequency, however, showed a significant decrease of -0.35 Hz on the operated side, only in the group with cortical infarction, whereas no frequency decrease was found in the other group. This unilateral postoperative frequency decrease in patients with cortical infarction is interpreted as a temporary deterioration of brain function.