Electroconvulsive therapy stimulus dose expressed as volume of seizure foci

Electrical stimulus dose is typically stated as charge in millicoulombs (mC), representing the number of electrons. However, by overlooking the voltage threshold for neuronal depolarization, charge alone is inappropriate. Any charge can accumulate from subthreshold voltage over time. Stimulus energy represents heat content; without a delivery rate, it is not related to depolarization voltage. The objective was to formulate stimulus dose in accordance with seizure induction physiology.

Stimulus dose was expressed as volume of generated seizure foci, a variable dependent on current and charge. A second more detailed model considers brain voltages as related to clinical deep brain stimulation.

For the constant current stimuli characteristic of widely available American stimulators, stimulus dose is proportional to current cubed multiplied by charge. This relationship corresponds to the 3 dimensions of a voltage field in space, where the volume above a certain voltage increases with the cube of the voltage radius. As a consequence, any particular charge at 0.9 A (ampere) current has a seizure foci dose approximately 50% higher than the same charge at 0.8 A.

The modeling offers an explanation for published measurements comparing instruments of maximum current 0.8 and 0.9 A. The modeling also suggests compensation approaches to be applied to the age-based bilateral stimulus dosing method. An electrical dosing strategy based on "half-age" (2.5 mC/y) is reasonable for 0.9-A stimulation but a "three-quarters age" (3.7 mC/y) is more appropriate for 0.8-A stimulation. The present results can allow doses and seizure thresholds to be compared between different currents, as when substituting one electroconvulsive therapy instrument for another.