Specifications of an electromyogram-driven neuromuscular stimulator for upper limb functional recovery

An electromyogram (EMG)-driven neuromuscular stimulator for upper limb functional recovery (Muraoka et al., 1998) can stimulate target muscles in proportion to the amount of voluntary EMG of the identical target muscles. Furthermore, it can facilitate the contraction of paralyzed muscles by electrical stimulation at subthreshold intensity level. Although it has been suggested that to use the stimulator for as long a time as possible might be needed for more effective treatment, the utilization time was limited by the size of the stimulator, which involved a laptop personal computer. To use in daily life, the device was improved to be a smaller size of 95×65×40 mm (including batteries) which was equivalent to a mobile phone (in 2002). The stimulator was called the Integrated Volitional-control Electrical Stimulator (IVES). IVES has already been manufactured and its use has spread in Japan since 2008. owadays, therapy using IVES is an effective therapy to improve the motor function of the upper limb in post-stroke patients with hemiparesis. However, the signal processing and internal structure of IVES has not yet been reported. In this study the device specification of IVES is described, especially its electrical circuits and signal processing that detect voluntary EMG and stimulate from the same electrodes. IVES uses two DIACs for detecting voluntary EMG from stimulating electrodes. The DIACs switch passively between the stimulation circuit and the EMG amplifier circuit. Furthermore, the signal processing of the time-shifted difference of the 2-cycle EMG signal following identical stimulation pulses eliminates stimulation artifacts and evoked potentials, and extracts voluntary EMG.