INFLUENCE OF BIPOLAR ESOPHAGEAL ELECTRODE POSITIONING ON MEASUREMENTSOF HUMAN CRURAL DIAPHRAGM ELECTROMYOGRAM

We aimed to describe how the human diaphragm electromyogram (EMGdi) is filtered at different positions within the esophageal hiatus, i.e., i n the close proximity of the diaphragm, when obtained with an array of bipolar electrode pairs mounted on an esophageal catheter. We defined the electrically active crural diaphragm musculature that covers the esophagus as the electrically active region of the diaphragm (EAR(di)) and its center as the EAR(di) center. EMGdi signals were obtained via a multiple-array esophageal catheter consisting of seven sequential e lectrode pairs with three different electrode configurations. Subjects (n = 5) performed voluntary contractions of the diaphragm at function al residual capacity. Visual inspection of the signals revealed revers al of signal polarity on either side of the EAR(di) center. Extreme co rrelation values (r values close to -1 at 0-ms time offset) were obser ved for the correlation of signals on either side of the EAR(di) cente r; moving peripherally from the EAR(di) center (caudally and cephalad) , the RMS increased to a peak (range of 2.1-4.1 dB for the different e lectrode configurations) and then decreased for the most peripheral el ectrode pairs. From a position where the RMS values peaked, center fre quency values increased at the EAR(di) center (range of 26-29 Hz for t he different electrode configurations). Computer simulation yielded si milar data to the experimental results. We conclude that electride pos itioning within the EAR(di) severely influences center frequency and R MS values and that the center of the EAR(di) can be identified cia cro ss-correlation analysis.