COMPARISON OF DIAPHRAGMATIC EMG POWER SPECTRA - SPONTANEOUS CONTRACTIONS VS EVOKED COMPOUND ACTION-POTENTIALS

The electromyogram (EMG) power spectrum from spontaneous diaphragm con tractions has been used to identify the development of fatigue. How ev er, power spectral analysis of the spontaneous diaphragmatic EMG signa l is limited and subject to error. In contrast, power spectral analysi s of the compound diaphragm action potential (CDAP) may be superior. T he aim of the present study was to determine whether the EMG power spe ctra of evoked CDAPs correlate with those of spontaneous diaphragm con tractions. Four anesthetized mechanically ventilated dogs with spontan eous isometric diaphragm contractions were studied using a mechanicall y isolated in situ diaphragm preparation. CDAPs were elicited via phre nic nerve stimulation, and intramuscular wire electrodes recorded EMG. Diaphragm temperature was changed from 40 to 30 degrees C to elicit c hanges in the EMG power spectra. The EMG signal from 10 spontaneous co ntractions and 10 CDAPs were acquired at 1 degrees C intervals. Fast F ourier transform was applied to both spontaneous and CDAP data yieldin g the power spectra, which were represented by their center frequencie s (f(c)). The CDAP f(c) correlated well with the EMG f(c) obtained fro m spontaneous contractions (r = 0.99). We conclude that evoked CDAPs m ay provide an accurate alternative to spontaneous contractions for EMG power spectral analysis of the diaphragm.