TECHNICAL NOTE - ESTIMATED ELECTRODE OPERATING-CONDITIONS OF THE FIRST LONDON MK V IMPLANTED STIMULATOR

The electrodes of an implanted stimulator must be operated in such a w ay that the task of converting an election current in metal to an ion current in tissue is achieved without release of noxious chemical spec ies into the tissue, and without significant corrosion of the electrod e metal. Both these effects depend on the charge density at which the electrodes are operated In bringing a newly designed multichannel stim ulator into service, the charge densities can only be Known when the o perating stimulus strengths have been determined Even then, unless the stimulator is arranged to telemeter out what it is doing, any charge- density figures obtained have the character of estimates, rather than measurements. The first London Mk. S stimulator is wed to enable a par aplegic woman to stand up This note provides estimates of the average charge density and corrosion rate for the Pt-Ir electrodes used. These fall within limits which we believe to be generally accepted as safe.