Development and clinical capabilities of a new implantable biostimulator

During the past nine years we have used experimentally and clinically various types of implantable electronic units to stimulate or block nerve impulses. Tissue tolerance and reliability have been excellent, but electronic design and production factors limited their versatility. Our recent studies, a part of the visual prosthesis program, revealed the importance of a need for a device with the capability of receiving a wide variety of signals. The type of current, wave form, pulse width, and frequency have proved to be of critical importance and the available devices cannot meet these demands. Our experiments have shown that for chronic electrical stimulation or inhibition of nervous tissue the most critical factor is “current density” at the point of contact. Heat production and impedance are other important considerations. The unit discussed has been designed and built to allow precise control of these parameters. Until recently the only neurosurgical methods to alter function of the nervous system were destruction of a given area or interruption of nervous pathways. In selected situations this has been effective but, generally, an associated loss of either motor or sensory function results. Electronic methods hold promise for selective or partial alteration of function that can be programmed according to a temporal schedule. An area can now be stimulated or blocked without local destruction. By controlled stimulation, information can be fed into the system which may alter the subjective response and the nature of the reflex arc, or even amplify cerebral inhibition. Using multiple circuits one structure can be stimulated while function in an adjacent area can be inhibited. The clinical application of the system is discussed with particular reference to the electronic control of pain secondary to malignant disease. A brief discussion is given regarding the probable origin of pain and how involved pathways can be altered electrically. Future clinical applications are mentioned.