[The effect of surface area of active recording electrode to CMAP parameters]

The purpose of this study is to quantitatively evaluate the effect of surface area of active recording electrodes to CMAP. The APB muscles from 19 young healthy subjects were included. The evoked CMAPs from median nerve supramaximal stimulation at wrist were recorded with regular surface disc electrode. Then the active recording electrode were changed to 1/2 surface area of disc, 1/4 surface area of disc, monopolar needle and concentric needle at the same recording sites. Computer reading of the latency, duration, amplitude and surface area of the CMAP were done and compared to that of standard electrode. Results disclosed that decrease the surface area of active recording did not significantly influence the distal latency, duration, amplitude and surface area of the CMAP (p > 0.1), although tendency to increase the amplitude and area were noted. The recording abilities of the active recording and the surface area difference between active recording and reference were considered to be the contributing factors. In clinical application such as recording an area with skin defect, the surface area of active recordling electrode can be altered without significant distortion of CMAP parameters.