Single-Channel Stimulation

Before the implementation of CES, stimulation site, pulse configuration, and the magnitude of parameters should be determined. and first assessed the optimal stimulation parameters and electrode sites for single-channel stimulation of CES, in cats with spinal cord injury (SCI). Two pairs of electrodes were separately implanted in a semicircular fashion, around the colon, at approximately 10 and 25 cm, respectively, proximal to the anus. Each electrode of a third electrode pair was separately implanted, parallel to the longitudinal axis of the intestine, at approximately 5 and 20 cm, respectively, proximal to the anus. The three electrode pairs were stimulated separately to determine the optimal stimulation site. Frequency (10 and 40 Hz), pulse width (0.1 and 1.0 ms), and pulse amplitude (0–50 mA) were respectively tested for each pair of electrodes to determine the optimal stimulation parameters. The results of colonic, transit measurement supported that CES could improve colonic transit. The electrode pair, which was most effective at promoting colonic transit, was located semicircularly, 10 cm proximal to the anus. The stimulation parameters were optimized for frequency at 40 Hz, for pulse width at 1 ms, and pulse amplitude between 25 and 35 mA. , however, proved that luminal content propulsion is highly dependent on pressure waves of the proximal colon; therefore, the proximal colon was chosen as the stimulation site in some CES studies. evaluated the acute effects of single-channel CES in rats. One pair of pacing wires was implanted on the serosal surface of the proximal colon, 1 cm distal to the cecocolonic junction, the point at which a fistula was made for phenol red injection to measure colonic transit. The electrical stimulus was composed of pulse trains with a train on-time of 2 s and train off-time of 3 s, a pulse frequency of 40 Hz, a pulse width of 4 ms, and pulse amplitude of 10 mA. The results, when compared to the control session, showed that the CES session exhibited a significantly higher output of phenol red, which indicated CES of the proximal colon could also accelerate colonic transit.

Besides stimulation of different sites, different pulse configurations were used in CES studies. To investigate the most effective pulse configuration, ) compared long-pulse CES and trains of pulses CES on colonic contractions and transit in a conscious canine model with a proximal colon cannula. For CES, one pair of serosal electrodes was placed and sutured, 10 cm distal to the cecum. In the long-pulse CES session, CES was applied with a pulse frequency of 20 pulses/min, a pulse width of 300 ms, and pulse amplitude of 2–6 mA (according to the tolerance of each animal). In the pulse-train CES session, CES was performed using a train on-time of 2 s and off-time of 3 s, a pulse frequency of 40 Hz, a pulse width of 6 ms, and a pulse amplitude of 2–6 mA (according to the tolerance of each animal). They found that, when compared with sham CES, pulse-train CES, but not long-pulse CES, significantly increased colonic contraction, accelerated colonic transit, and induced defecation.

In clinical research on CES, Shafik et al., in their early studies, determined the rectosigmoid junction, which played the role of functional sphincter in defecation, as the potential pacemaker site of rectal electrical activity ( ). After that, in 10 constipation patients with rectal inertia, they implanted one pair of stimulation electrodes and two pairs of recording electrodes into the rectosigmoid junction mucosa for rectal pacing ( ). The electrical stimulator delivered long pulses with a pulse width of 200 ms, an amplitude of 5 mA, and a frequency that was 15% higher than the frequency of the basal, rectal waves already recorded. All patients were trained for electrical stimulation treatments at home, with instructions to perform rectal electrical stimulation 30–60 min after breakfast and lunch and record the daily number of induced and spontaneous bowel evacuations. With rectal pacing, rectal electrical activity of 10 patients was recovered at different degrees, and bowel evacuation was induced in 7/10. The other 3/10 who exhibited low electrical activity showed no significant response to the rectal pacing treatment. Three of the seven patients could evacuate spontaneously without pacing after having performed daily pacing for 5–6 months, and their pacing devices were removed thereafter. The study period was well tolerated, acceptable to the patients, and performed without complication. Similarly, also chose the rectosigmoid junction to conduct electrical stimulation on two patients with refractory, slow-transit constipation. One pair of electrodes was placed into the muscular layer of the rectosigmoid junction under laparoscopy. The stimulation parameters used were a frequency of 10 Hz, a pulse width of 150 μs, and pulse amplitude of 2 V in a continuous mode for 30 days. After 30 days, the mode was changed to a cyclical mode, with electrical stimulation, 2 min on and 20 min off. During the follow-up of 19 months and 6 months, respectively, in these two patients, the number of bowel movements per week increased significantly. Both patients no longer needed laxatives, enemas, or any other assistance for defecation.

In addition to the clinical research mentioned earlier, a noninvasive electrical stimulation therapy using an anal plug has been applied to treat functional constipation. The first trial of this therapy was conducted by . They treated a 25-year-old female patient with functional constipation who displayed impaired, rectal sensation without slow-transit or paradoxical pelvic floor contraction. After receiving electrical stimulation therapy, her constipation symptoms and impaired rectal sensations improved dramatically. After this case report, the authors selected 22 patients, who also had functional constipation with impaired rectal sensation, to compare electrical stimulation therapy with biofeedback therapy ( ). The stimulation parameters used were scheduled individually and within the range of a frequency of 2–110 Hz, a pulse width of 360–960 μs, and amplitude of 30–35 V. The stimulation therapy was performed once a day for 20 min, over 10–12 sessions. They showed that the efficacy of electrical stimulation treatment is comparable to the efficacy of biofeedback therapy in this subgroup of constipated patients, and that the frequency of the sense of “wanting to defecate” improved only in the group treated with electrical stimulation. reported on the efficacy of this therapy that was based on five years of clinical experience from 147 patients with chronic, functional constipation. They found that electrical stimulation with the anal plug was successful for the treatment of patients with chronic, functional constipation, refractory to biofeedback therapy, rectal hyposensitivity, and anal pain. Electrical stimulation therapy, however, provided no significant improvement in colonic transit time in their patients.