A new instrument for continuous recording of the evoked compound electromyogram in the clinical setting

To study neuromuscular transmission, observation of the evoked compound electromyogram (EMG) has important advantages over observation of the evoked mechanical muscle contraction. Technically, however, recording of the evoked compound EMG, especially in continuous study of several hours duration, has been difficult. Investigators have employed various complicated systems, including tape recording, photorecording, and photographing for such purposes. The authors have applied modern computer technology to construction of an EMG analyzer which enables handling the evoked EMG even more easily than the evoked mechanical contraction. The principle involves digital dissection, storage with memory, readout with time expansion, and analog reconstruction of the compound EMG. The signal can be recorded with ease by use of any suitable hot-stylus or ink-writing oscillographic recorder. Both the waveform and the amplitutde of the EMG can be on-line recorded. The cost compares favorably with comparable devices for similar studies.