Effects of muscle-to-electrode distance on the human diaphragm electromyogram. Beck, J., C. Sinderby, J. Weinberg, and A. Grassino. Meakins Christie Laboratories, McGill University, Notre Dame Hospital, University of Montreal, Montreal, Quebec, Canada, Spinal Injuries Unit, Sahlgrenska Hospital, G[diaeresis]oteborg, Sweden and S[diaeresis]oder Hospital, Stockholm, Sweden
APStracts 2:0239A, 1995.
It has been suggested that esophageal recordings of the diaphragm electromyogram (EMGdi) are influenced by changes in chest wall configuration. Whether the changes are of physiological or artifactual origin is unclear. For example, the distance between the esophageal electrode and the diaphragm is likely to alter with chest wall configuration, and may lead to mis-interpretations of EMGdi. The aims of this study were: (1) to evaluate and to quantify the effect of the muscle-to-electrode distance filter (MEdist filter) on EMGdi, as obtained with a multiple array esophageal electrode, (2) to take advantage of the MEdist filter in order to locate the position of the diaphragm with respect to the electrode, and (3) to evaluate the influence of lung volume and chest wall configuration on EMGdi center frequency (CF), while controlling for the MEdist filter, and signal quality. Five subjects performed six static contractions of the diaphragm at each of seven chest wall configurations, as evaluated by the method of Konno and Mead. EMGdi was measured with seven pairs of electrodes mounted on an esophageal catheter. The pair of electrodes whose EMGdi power spectrums were the least filtered by the MEdist was assumed to be closest to the diaphragm. The results of the study indicated (1) EMGdi power spectrums were strongly affected by the distance between the diaphragm and the electrodes. CF decreased by approximately 1 Hz per mm displacement away from the electrode pair closest to the diaphragm. (2) There was no systematic relationship found between changes in chest wall configuration and CF, when CF was measured from the electrode pair closest to the diaphragm. We conclude that the EMGdi CF can be reliably measured with a multiple array esophageal electrode which covers the span of diaphragmatic excursion, and by selecting the pair of electrodes which is the closest to the diaphragm. 

Received 18 October 1994; accepted in final form 27 April 1995.
APS Manuscript Number A1072-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  8 June 1995.