Calculations of the pH changes produced in body tissue by a spherical stimulation electrode

A mathematical description of pH excursions produced in interstitial fluid by a spherical stimulation electrode is presented. The pH is calculated as a function of current density, electrode radius, distance, time, and pulsing regimen for an electrode driven by biphasic current pulses. Calculations indicate that large pH excursions occur around electrodes pulsed at current densities used for neural stimulation. For an electrode with a radius of about 1 micron these transient pH changes extend only a few micrometers from the electrode surface. The practical importance of these pH changes remains to be determined.