Effect of Intraesophageal Electrode Position on Signal Amplitude of the Crural Diaphragm Electromyogram

We studied the effect of electrode position relative to the lower esophageal sphincter (LES) on the crural diaphragm electromyogram (EMG) recording in 15 healthy human subjects. Three coil electrodes, each 1 cm in axial length and spaced 1 cm apart, were positioned on the distal 5 cm of a 6-cm-long Dent sleeve device. Bipolar EMG signals were recorded simultaneously from proximal and distal pairs of electrodes during spontaneous respiration, maximum inspiration with open airway, and maximum inspiration with closed airway. The catheter was positioned so that the side hole at the proximal margin of the sleeve recorded esophageal pressure just above the upper end of the LES. During spontaneous inspiration, the amplitude of the proximal diaphragm EMG signal was significantly higher than the distal. There was a significant difference in the amplitude of the two diaphragm EMG signals during maximum inspiration with open airway, and nearly significant differences in the two EMG signals during maximum inspiration with closed airway. We found that electrode position strongly influences the amplitude of the crural diaphragm EMG signals as measured by intraesophageal electrodes. Assessment of the crural diaphragm EMG with only one pair of electrodes may underestimate the signal amplitude.