MINIATURIZED ELECTRICAL STIMULATOR WITH CONTROLLABLE DUTY CYCLES

A stimulator with adjustable duty cycles is described for chronic elec trical stimulation of skeletal muscles by way of a motor nerve. The st imulator is unique in that it can stimulate a muscle or group of muscl es for 2-h intervals that alternate with variable periods of rest (2, 4, 6, 8, or 10 h). A given duty cycle is selected with a rotary switch at the beginning of an experiment and will continue automatically, wi thout human intervention, for the duration of the experiment. Other fe atures include an adjustable voltage output, a stimulation indicator l ight-emitting diode (LED), and a low-battery indicator LED. The stimul ator is powered by two 9-V batteries or can be used with a bench-top p ower supply. The stimulation frequency (10 Hz) and pulse width (300 mu s) are fixed in our design but can be changed to other values by subs tituting two of the resistors and one capacitor in accordance with sim ple formulas. We have used the stimulator in rat and rabbit experiment s to stimulate the anterior tibialis and extensor digitorum longus mus cles for up to 60 days. The timing and output of the stimulator were f ound to be stable and accurate over the entire 60-day period. The stim ulator and batteries were carried in a jacket worn by the rabbits. In the rat experiments, the stimulator was used in a remote fashion with the electrical leads connected to the animals by way of a tethering sy stem. In both animals, the electrodes were implanted adjacent to the c ommon peroneal nerve. The 60 days of electrical stimulation caused ext ensive angiogenesis in the skeletal muscles, demonstrating the effecti veness and reliability of the stimulator in chronic studies. The stimu lator should thus be useful in long-term studies of blood vessel growt h and skeletal muscle adaptations to long-term muscle stimulation.