Electrical stimulation of the brain. II. Effects on the blood-brain barrier.

Acute and chronic studies of the effects of electrical stimulation on the blood-brain barrier (BBB) of the cat cerebral cortex are reported. The findings emphasize the importance of avoiding direct-coupled, monophasic waveforms in stimulating nervous tissue. Biphasic waveforms with balanced charges in each half-wave of the stimulating pulse can be used for up to 36 hours of continuous stimulation if the charge per phase (Q/ph) does not exceed 0.45 microcoulombs. Charge density (QD) is also an important parameter. When stimulating in the bipolar mode, BBB breakdown will occur first beneath the smaller electrode of the pair. Following electrical injury, the BBB will be partially restored within one week, and, with rare exceptions, be completely intact after one month.