Influence of the bipolar electrode transfer function on the electromyogram power spectrum

This study demonstrates the impact of the bipolar electrode transfer function on the canine diaphragm electromyogram (EMG) power spectrum, as evaluated with a new electrode design and implantation technique. The results show that: (a) changes in interelectrode distance transformed single-peaked power spectrums into double-peaked spectrums; (b) the mean action potential conduction velocity (APCV), and power spectrum center frequency (CF) and median frequency (MF), are related for interelectrode distances of 5 and 10 mm, but not for 15 and 20 mm; and (C) CF, MF, -3-dB, and -6-dB bandwith values depend on interelectrode distance. We conclude that bipolar electrodes, with a nonfixed interelectrode distance, cannot be used for physiological interpretations of the EMG power spectrum. Nonetheless, power spectrums obtained with fixed and appropriate interelectrode distances can be trusted, if the electrodes are positioned in the direction of the muscle fibers and in regions with low densities of motor endplates.