Use of a neuromuscular stimulator to increase anal sphincter pressure.

OBJECTIVES: The objective of this study was to determine if short periods of electrical stimulation with perianal electrodes could increase anal pressures. MATERIAL AND METHODS: Anorectal responses to electrical stimulation were evaluated in five healthy SCI patients. Anorectal pressures were recorded with a small pressure-recording balloon before, during, and immediately following stimulation. A battery-powered stimulator with self-adhering surface electrodes, two inches in diameter was used. Stimulating parameters consisted of 300 micros pulse duration, 35 Hz stimulating frequency. A current response study was conducted by using short periods of electrical stimulating with currents from 0-100 mA until a maximal pressure was recorded. Each current setting was conducted for 13.2+/-9.7 s before increasing to the next higher current, and fatigue was reduced by including a 5-minute rest between stimulations. RESULTS: Four of the five subjects had strong anal contractions with perianal stimulation. Increases in pressure ranged from 38 to 125 cm H2O based on maximal responses at currents ranges of 60 to 100 ma. Even during the short periods of stimulation used here, fatigue was apparent. There was an average drop of 11% in anal pressure over the 13 s of stimulation. Rectal pressures were unchanged with perianal stimulation. CONCLUSIONS: Perianal stimulation with surface electrodes is an approach that might be considered in the future for management of fecal incontinence in individuals with spinal cord injury. Further studies are needed to assess the feasibility of using chronic perianal surface electrical stimulation to sustain anal sphincter contractions.

Effects of low charge injection densities on corrosion responses of pulsed 316LVM stainless steel electrodes.

The safe charge injection density for pulsing of 316LVM electrodes has been reported to be 40 microC/cm2. However, only 20 microC/cm2 is available for nonfaradic charge transfer and double layer charge injection. Therefore, we evaluated long term pulsing at 20 microC/cm2 with capacitor coupling.

Comparison of electrical transients and corrosion responses of pulsed MP35N and 316LVM electrodes.

Functional neuromuscular stimulation (FNS) is often limited by electrode malfunctions such as corrosion and breakage, particularly for intramuscular and epimysial type electrodes. As a result, the electrochemical charge injection characteristics and corrosion responses of single strand 316LVM stainless steel and MP35N nickel-cobalt alloy electrodes were evaluated in vitro. For charge balance, capacitor coupled monophasic protocols with varying charge injections were employed. Electrodes were evaluated with either positive-first or negative-first pulses, 60 Hz, 100 microsec pulse duration, and stimulation periods from 100 to 240 hours. Charge injection densities ranged from 20 to 80 microC/cm2. For both anodic-first and cathodic-first pulsing, the potential transients for the MP35N electrodes were more extreme than for the 316LVM electrodes over the test period, and increased corrosion was apparent on the MP35N electrodes from both optical and scanning electron microscopy. Therefore, 316LVM, but not MP35N, may be suitable for FNS applications with charge injection densities less than 40 microC/cm2.

Comparison of 316LVM and MP35N alloys as charge injection electrodes.

An In vitro comparison of the corrosion response of 316LVM stainless steel and MP35N (a CoNiCrMo alloy) electrodes under conditions appropriate to applications in functional electrical stimulation (FES) was made. Electrodes of both alloys were subjected to a cathodic 40 microC/cm2 charge injection protocol and the potential transient response was recorded over a 96 h period. The transient responses were compared with potentiodynamic polarization data used to establish the quasiequilibrium response of the alloys in the carbonate and phosphate-buffered saline electrolyte used in the study. The MP35N electrodes exhibited extensive pitting corrosion during charge injection, whereas little corrosion was observed on 316LVM electrodes. An explanation for the susceptibility of MP35N to corrosion during charge injection is found in the potentiodynamic polarization data, which reveal a breakdown potential (critical pitting potential) of 0.45 V (SCE) for MP35N compared with 1.05 V (SCE) for 316LVM. Factors that may influence corrosion response during charge injection from alloys exhibiting active-passive behavior are discussed.

Evaluation of direct bladder stimulation with stainless steel woven eye electrodes.

Encouraged by recent clinical reports of micturition induced in patients by direct bladder stimulation, we conducted a study of optimum methods of direct bladder stimulation. During surgery six male cats received eight large surface-area woven eye electrodes sutured to the bladder wall serosa, four on the bladder dome and four adjacent to the trigone area. Two additional small surface-area single knot electrodes were sutured in the trigone area. Suprapubic and intraperitoneal tubes were placed for pressure recording and bladder filling. Leg and pelvic floor EMG electrodes were also used for tethered recordings. One to eight weeks after surgery, optimum stimulation methods were evaluated as the animal freely moved about a urodynamic recording cage. Electrodes in the trigone region were more effective than electrodes on the dome and induced bladder contractions and voiding similar to spontaneously induced voiding with bladder filing. Large surface area, woven eye electrodes, composed of multistranded 316LVM stainless steel wire, were more effective than smaller surface area single knot electrodes. High stimulating frequencies (40 Hz) were better than lower frequencies (10 to 20 Hz), and a 1 millisecond pulse duration was optimal. Pulsing with stimulating currents from 10 to 25 mA induced effective bladder contractions with voiding when applied for 3 seconds. However, lower currents using longer stimulation periods were also effective. Bipolar electrodes with both electrodes on the bladder wall were superior to monopolar arrangements with the positive ground electrode along the animal's back. We concluded that in the able-bodied cat model, bladder contractile activity for micturition can be induced with direct bladder stimulation and with little discomfort. An effective stimulation protocol consists of capacitor-coupled monophasic pulses with large surface area bipolar electrodes in the trigone region. Stimulating parameters of 40 Hz, 1 msec., 10 to 25 mA applied for 3 seconds were optimal. In addition, based on corrosion resistance observations, the electrodes are quite suitable for long-term studies.