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Optimal electrode placement for noninvasive electrical stimulation of human abdominal muscles

Prince of Wales Medical Research Institute and University of New South Wales, Randwick, Sydney, Australia

Submitted 6 August 2006 ; accepted in final form 15 December 2006

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 noninvasive electrical activation of the abdominal muscles. In six healthy subjects, we compared twitch pressures produced by a single electrical pulse through surface electrodes placed either posterolaterally or anteriorly on the trunk with twitch pressures produced by magnetic stimulation of nerve roots at the T₁₀ level. A gastroesophageal 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 posterolaterally 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; means ± SE). At TLC, twitch pressures were larger. The values for posterolateral electrical stimulation were comparable to those evoked by thoracic magnetic stimulation. The posterolateral stimulation site is the optimal site for generating gastric and esophageal twitch pressures with electrical stimulation.

cough; functional electrical stimulation; abdomen