Diaphragm interference pattern EMG and compound muscle action potentials: effects of chest wall configuration

Beck, Jennifer, Christer Sinderby, Lars Lindström, andAlex Grassino. Diaphragm interference pattern EMG and compound muscle action potentials: effects of chest wall configuration. J. Appl. Physiol. 82(2): 520-530, 1997.The effect of chest wall configuration on the diaphragmelectromyogram (EMGdi) was evaluated in five healthy subjects with anesophageal electrode for both interference pattern EMGdi (voluntarycontractions) and electrically evoked diaphragm compound muscle actionpotentials (CMAPs). Diaphragm CMAPs (both unilateral and bilateral)were evaluated for the baseline-to-peak amplitude (Ampl), the time fromthe onset of the CMAP to first peak (T1), root mean square (RMS), andcenter frequency (CF) values of the CMAP power spectrum. CF values fromthe interference pattern EMGdi power spectrum were also calculated. ForCMAPs obtained at an electrode position least influenced by variationsinduced by electrode positioning, Ampl increased with diaphragmshortening from functional residual capacity (FRC) to total lungcapacity (TLC) by 101 and 98% (unilateral and bilateral,respectively). Bilateral CMAP RMS values increased 116% from FRC toTLC. CMAP T1 values decreased with diaphragm shortening from FRC to TLC by 1.1 and 2.1 ms for the unilateral and bilateral stimulations, respectively, and CF increased for the bilateral diaphragm CMAPs withdiaphragm shortening. CF values from the interference pattern EMGdi didnot show any consistent change with chest wall configuration. Thus CFvalues of the interference pattern EMGdi obtained with an esophagealelectrode can be considered reliable for physiological interpretation,at any diaphragm length (if electrode positioning and signalcontamination are controlled for), contrary to the diaphragm CMAPs,which are sensitive to changes in chest wall configuration. It isspeculated that the different results (over the effects of chest wallconfiguration on interference pattern EMGdi and diaphragm CMAPs) may bebecause of summation properties of the signals and how these influencethe EMG power spectrum.