Effects of chest wall configuration on diaphragm interference
pattern emg and compound muscle action potentials.
Beck, Jennifer, Christer Sinderby, Lars Lindstr[diaeresis]om, and Alex
Grassino.
Meakins Christie Laboratories, McGill University, and Notre Dame
Hospital, University of Montreal, Montreal, Quebec, Canada. H2L 4M1,
Spinal Injuries Unit, Sahlgrenska Hospital, University of
G[diaeresis]oteborg, G[diaeresis]oteborg, Sweden
APStracts 3:0472A, 1996.
The effect of chest wall configuration on the diaphragm electromyogram
(EMGdi) was evaluated in five healthy subjects with an esophageal
electrode for both interference pattern EMGdi (voluntary
contractions) and electrically evoked diaphragm compound muscle
action potentials (CMAPs). Diaphragm CMAPs (both unilateral and
bilateral) were evaluated for the baseline-to-peak amplitude (AMPL),
the time from the onset of the CMAP to first peak (T1), the root
-mean-square (RMS), and center frequency (CF) values of the CMAP power
spectrum. CF values from the interference pattern EMGdi power
spectrum were also calculated. For CMAPs obtained at an electrode
position which was the least influenced by variations induced by
electrode positioning, AMPL increased with diaphragm shortening from
functional residual capacity (FRC) to total lung capacity (TLC) by
101% and 98% (unilateral and bilateral, respectively). Bilateral CMAP
RMS values showed a 116% increase from FRC to TLC. CMAP T1 values
decreased with diaphragm shortening from FRC to TLC by 1.1 ms and 2.1
ms for the unilateral and bilateral stimulations, respectively, and
CF increased for the bilateral diaphragm CMAPs with diaphragm
shortening. CF values from the interference pattern EMGdi did not
show any consistent change with chest wall configuration. In
conclusion, CF values of the interference pattern EMGdi obtained with
an esophageal electrode can be considered as reliable for
physiological interpretation, at any diaphragm length (if electrode
positioning and signal contamination are controlled for), contrary to
the diaphragm CMAPs, which are sensitive to changes in chest wall
configuration. It is speculated that the different results (over the
effects of chest wall configuration on interference pattern EMGdi and
diaphragm CMAPs) may be due the summation properties of the signals
and how these influence the EMG power spectrum.
Received 1 December 1995; accepted in final form 18 September
1996.
APS Manuscript Number A376-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996