Recruitment data for nerve cuff electrodes: implications for design of implantable stimulators

Recruitment characteristics of nerve cuff electrodes, implanted in four cats for five months, were measured. Monopolar, bipolar, and tripolar configurations were considered. Approximately twice the current was required to achieve a given response using the tripolar configuration as compared with monopolar stimulation. Bipolar stimulation also required more current than did monopolar stimulation. A number of strategies for modulating muscle tension were considered using the recruitment data. It was shown that both pulse amplitude and pulse duration should be software-selectable to achieve adequate control of muscle tension when using either pulse-amplitude modulation or pulse-duration modulation. The effects of pulse-amplitude and pulse-duration step size on the maximum step change in muscle tension and the linearity of the recruitment curves were examined. The use of logarithmic steps in the modulation parameter was examined and shown to result in improved controllability and linearity.