A stimulator for functional activation of denervated muscles

In recent years various studies proved that electrical stimulation can improve contractile capability and restore muscle function in long-term denervated degenerated muscles. The low excitability of the muscle cells at the initial stage of training and surrounding connective tissue, acting as an electrical shunt, require special stimulation parameters. Until now, no appropriate devices (stimulators) are commercially available. Therefore, we were forced to design our own stimulators. The control unit of the stimulators is based on a microprocessor for maximum flexibility regarding the generation of the parameters such as pulse amplitudes, pulse width, frequency, stimulation times, ramps, and so on. In addition, the microprocessor design allows recording of compliance data such as stimulation date, time, duration, and used programs. The constant voltage output stage of the stimulator is able to generate biphasic charge balanced stimulation impulses with a pulse width of 1 to 300 ms, voltage amplitudes up to +/-80 V (160 VPP), and stimulation currents up to 250 mA. To prevent direct current due to inexact charge compensation, the electrode outputs are decoupled capacitively. Simultaneous 2 channel stimulation with independent intensity levels is possible. The stimulators are programmed using a notebook or a personal digital assistant via infrared serial interface. This concept guarantees the application of correct stimulation parameters because the patient has only access to parameters that are preprogrammed for him in the outpatient clinic. For the home based training, access is limited to variation of intensity within preprogrammed limits. For safety reasons, the portable unit is powered by an internal rechargeable battery. High efficiency switched voltage regulators are used to provide the different required voltage levels while ensuring an acceptable operating time of the stimulator.