DETERMINATION OF SPECIFIC CEREBRAL IMPEDANCE AND CEREBRAL CURRENT DENSITY DURING APPLICATION OF DIFFUSE ELECTRICAL CURRENTS

Methods are presented for determining the specific cerebral impedance and current density during the application of diffuse electrical currents such as those used for electroanesthesia. In experiments with monkeys, the average cortical and thalamic specific impedances remained within 5 per cent of the control value for electroanesthesia currents equal to twice those needed for surgical intervention. The current density in these regions was linearly proportional to the applied current. Simulation experiments were conducted to obtain a suitable correction factor for the influence of subcortical matter on cortical impedance. Current densities within the cortex and thalamus were within 2 standard deviation of each other. The minimal changes in cortical specific impedance in the absence of flat electrocorticogram suggest a spreading depression is not present during electroanesthesia. Since no general trend in impedance was observed during application of the electroanesthesia currents and the pulmonary and cardiovascular systems were stable, substantial circulatory changes or anoxia do not appear to be present during electroanesthesia. Since the brain current density was linearly proportional to the applied currents, prediction of the brain current density can be made from the application of various types of currents used in this study. © 1969 International Federation for Medical and Biological Engineering.