Development of an Implantable Muscle Stimulator: Measurement of Stimulated Angiogenesis and Poststimulus Vessel Regression

Abstract

We developed a lightweight, totally implantable electrical stimulator designed to elicit contraction of skeletal muscle. The stimulator can be programmed to run for different on-off intervals in a given time period in a fully automatic mode. Using the stimulator, angiogenesis was promoted in order to study the rate at which vessel growth and subsequent regression occurs after stimulus removal. A fully implanted digital stimulator was designed and fabricated. The stimulator was embedded subcutaneously in the thoracolumbar region of male Sprague-Dawley rats and the electrodes were tunneled under the skin to the common peroneal nerve of the right hind limb. The stimulator elicited muscle contraction in the hind limb at 10 s-1 using square-wave pulses 0.3 ms in duration, evoking contraction of specific muscles for 8 hours/day for 7 days. Chronic stimulation of the skeletal muscles innervated by the common peroneal nerve led to significant increases in blood vessel density in the tibialis anterior (TA; 26%) and the extensor digitorum longus (EDL; 19%) within 7 days. The vessel density remained elevated at 3 days and 7 days poststimulation, but subsequently decreased to control levels by 14 days poststimulation. The new stimulator can promote significant increases in vessel density within 7 days, allowing study of both stimulated vessel growth and poststimulus rarefaction. Because of its small size and reliable timing cycles, the stimulator should prove to be a valuable tool in studying these phenomena.