Influence of bipolar esophageal electrode positioning on
measurements of human crural diaphragm emg .
Beck, Jennifer, Christer Sinderby, Lars Lindstr[diaeresis]om, and Alex
Grassino.
Meakins Christie Laboratories, McGill University,
H[circumflex]opital Notre-Dame, Universit[acute]e de Montr[acute]eal,
Montreal, Quebec, Canada, Spinal Injuries Unit, Sahlgrenska Hospital,
Gothenburg, Sweden
APStracts 3:0204A, 1996.
The aim of the present study was to describe how the human diaphragm
electromyogram (EMGdi) is filtered at different positions within the
esophageal hiatus i.e. in close proximity to the diaphragm, when
obtained with an array of bipolar electrode pairs mounted on an
esophageal catheter. We defined the electrically active crural
diaphragm musculature which covers the esophagus as the electrically
active region of the diaphragm (EARdi) and its' center, the EARdi
center. EMGdi signals were obtained via a multiple array esophageal
catheter, consisting of 7 sequential electrode pairs with three
different electrode configurations. Subjects (n=5) performed
voluntary contractions of the diaphragm at functional residual
capacity, while maintaining a position of the electrode array (with
guidance from an on-line display) such that the most central pair of
electrodes, electrode pair 4, received a signal which was high in
center frequency (CF) and low in the root-mean-square (RMS).
Selection of the EMGdi samples used in the analysis was performed
off-line. Visual inspection of the signals (of all electrode pairs)
revealed reversal of signal polarity on either side of electrode pair
4, as well as a reduction in amplitude at electrode pair 4. Cross
-correlation analysis allowed the electrode pair closest to the center
of the EARdi to be determined. Extreme correlation values (r values
close to -1, at zero time offset) were observed for correlation of
signals on either side of the EARdi center. RMS was reduced at the
EARdi center; moving peripherally from the EARdi center (caudally and
cephalad), RMS increased to a peak (range 2.1 - 4.1 dB for the
different electrode configurations), and then decreased for the most
peripheral electrode pairs. From a position where the RMS values
peaked, CF values increased at the EARdi center (range 26 -29 Hz for
the different electrode configurations). Computer simulation of power
spectrums for perpendicular bipolar recordings yielded similar data
to the experimental results. We conclude that electrode positioning
within the EARdi severely influences CF and RMS values, and that the
center of the EARdi can be identified via cross-correlation analysis.
Received 12 September 1995; accepted in final form 4 April 1996.
APS Manuscript Number A1000-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96