Appendix A: Experimentation at Duke University
Frank W. Clippinger, Jr., M.D.
A system to provide a patient with sensation while he is using an upper-limb prosthesis is under development at Duke University. This system operates by means of a surgically implanted, induction-coupled RF (radio frequency) receiver-pulse generator which applies a direct electrical stimulation to the median nerve of the amputee's stump (Fig. 1 ). This generator delivers a fixed voltage stimulus to the nerve at a rate that varies in proportion to the pressure applied on a voluntary-closing prosthetic hand or hook. The transducer is a strain gauge, mounted either in a finger of the terminal device or the transmission cable of the prosthesis. The transmitter package and the power supply are contained within the distal forearm section of the prosthesis (Fig. 2-A and Fig. 2-B ).
Several patients have been fitted with this system. Response has been consistent in that all amputees report paresthesias that are referred to the peripheral distribution of the median nerve. These stimuli can be interpreted in terms of the force applied.
The experimental phase of the project is incomplete, but early results are encouraging.
Duke University Medical Center Durham, North Carolina