Electrolytic current-control elements for surgically implanted electrical devices

A useful circuit element for implantation, which is simple, robust and comparatively cheap, is a column of saline, isotonic with the body's extracellular space, to the ends of which connection is made via a pair of platinum electrodes. Column and electrodes are supported by a body of silicone rubber. By deforming the rubber so as to vary the cross-section of the column, the apparent resistance between the electrodes may be continuously varied; or one may 'pinch off' the column altogether, forming a switch. The name 'electrolytic' is used to imply that the device contains electrolyte, not that electrolysis occurs. Two successful applications to neurological prostheses are described, one to a facial nerve stimulator, the other to stimulate the pudendal nerves upon rise in urinary bladder pressure as a means of treating severe urinary incontinence.