Submitted on August 6, 2006
Accepted on December 15, 2006
Optimal electrode placement for non-invasive electrical stimulation of human abdominal muscles
Julianne Lim1, Robert B Gorman1, Julian Peter Saboisky1, Simon Gandevia1*, and Jane E Butler2
1 Prince of Wales Medical Research Institute, Sydney, New South Wales, Australia; University of New South Wales, Sydney, New South Wales, Australia
2 Prince of Wales Medical Research Institute, Randwick, New South Wales, Australia; University of New South Wales, Sydney, New South Wales, Australia
* To whom correspondence should be addressed. E-mail: s.gandevia.jap{at}unsw.edu.au.
Abdominal muscles are the most important expiratory muscles for coughing. Spinal cord injured patients have respiratory complications because of abdominal muscle weakness and paralysis and impaired ability to cough. We aimed to determine the optimal positioning of stimulating electrodes on the trunk for the non-invasive electrical activation of the abdominal muscles. In 6 healthy subjects, we compared twitch pressures produced by a single electrical pulse through surface electrodes placed either postero-laterally or anteriorly on the trunk to twitch pressures produced by magnetic stimulation of nerve roots at the T10 level. A gastro-esophageal catheter measured gastric pressure (Pga) and esophageal pressure (Pes). Twitches were recorded at increasing stimulus intensities at functional residual capacity (FRC) in the seated posture. The maximal intensity used was also delivered at total lung capacity (TLC). At FRC, twitch pressures were greatest with electrical stimulation postero-laterally and magnetic stimulation at T10 and smallest at the anterior site (Pga, 30±3 and 33±6 cmH2O vs. 12±3 cmH2O; Pes, 8±2 and 11±3 cmH2O vs. 5±1 cmH2O; mean±SE). At TLC twitch pressures were larger. The values for postero-lateral electrical stimulation were comparable to those evoked by thoracic magnetic stimulation. The postero-lateral stimulation site is the optimal site for generating gastric and esophageal twitch pressures with electrical stimulation.
