Optimal electrode placement for noninvasive electrical stimulation of human abdominal muscles

Abstract

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 T 10 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 T 10 and smallest at the anterior site (Pga, 30 Ϯ 3 and 33 Ϯ 6 cmH 2O vs. 12 Ϯ 3 cmH2O; Pes 8 Ϯ 2 and 11 Ϯ 3 cmH2O vs. 5 Ϯ 1 cmH 2O; means Ϯ 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 PEOPLE WITH HIGH-LEVEL SPINAL cord injury (SCI) are up to 150 times more likely to die from pneumonia, at any time after their injury, compared with the general population. Respiratory complications are the major cause of death in acute SCI patients (22). Reduced ability to cough and the subsequent buildup of pulmonary secretions result in respiratory complications, including atelectasis, sputum retention, pneumonia, and pleural effusion.The abdominal muscles are the major group of muscles that develop expiratory force, required to cough. Although functional electrical stimulation (FES) has been widely used to assist paralyzed limb muscles to regain function, there are fewer reports of the use of electrical or other types of stimulation on paralyzed human abdominal muscles, and so far they have had limited success in producing an effective cough (6,10,12,14,16,17,20,21,30,31,33).There have been several studies investigating the use of electrical stimulation over the anterior abdominal wall near the midline to measure the ability to generate expiratory flow or pressure (12,18,21,30,31). The most successful of these studies increased mouth pressure by 33 cmH 2 O during a tetanically stimulated maximal expiratory maneuver in tetraplegic subjects (21).As an alternative to electrical stimulation on the anterior wall of the abdomen, other groups have used magnetic stimulation over the T 10 spinous process to activate the spinal nerve roots around this level (T 8 -T 12 ). The benefit of magnetic stimulation is that it is r...

Respiratory muscle pacing with chronically implanted intramuscular Permaloc electrodes: A feasibility study

“…In addition, clinical studies with abdominal surface electrodes and electrodes on the lower ventral side of the spinal cord have produced exhaled volumes greater than 1 L [10][11][12][13][14][15]18]. These large exhaled volumes provide a standard for comparison of alternative techniques.…”

“…Second, higher stimulating currents should produce stronger muscle contractions. For example, up to 100 mA is used with surface electrodes over abdominal muscles [10][11][12][13][14]. Third, current implantation sites in the midabdominal muscles may not be optimal, because this location is distal to the origin of lower thoracic nerves that innervate the abdominal muscles.…”

“…In patients [10][11][12][13][14][15][16][17][18] and laboratory animals [5][6][7]19], stimulation of extradiaphragmatic respiratory muscles has been achieved with the use of ventral epidural electrodes, electrodes implanted at the spinal foramina close to the ventral roots, and surface electrodes (expiratory muscles). The feasibility of pacing upper-intercostal and abdominal muscles plus the diaphragm with chronically implanted intramuscular electrodes (Permaloc, Synapse Biomedical, Inc) * remains uncertain.…”

Respiratory responses to stimulation of abdominal and upper-thorax intercostal muscles using multiple Permaloc®electrodes

“…In patients [5][6][7][8][9][10][11][12][13][14] and laboratory animals [15][16][17][18], stimulation of extradiaphragmatic abdominal and upperthoracic respiratory muscles has been accomplished centrally with spinal epidural electrodes and peripherally with implanted and surface electrodes. Although large respiratory volumes were achieved from the extradiaphragmatic muscles with both of these approaches, they have not been extended to general SCI respiratory care.…”

Abdominal stimulation for respiratory support in tetraplegia: A tutorial review

“…The abdominal muscles are typically stimulated through surface electrodes which are easy to apply, and stimulation results in a uniform, welldefined muscle response [15], [16]. Alternatively, stimulation can be delivered by spinal cord stimulation using epidural electrodes [17] or microstimulators [18], or by magnetic stimulation of the thoracic nerve roots [19], [20].…”