Electrical impedance, a sensory system for detection of rectal filling after anorectal reconstruction: experimental study of rectal impedance measurements and defecation in dogs.

BACKGROUND: Total anorectal reconstruction with dynamic graciloplasty is an alternative to a permanent colostomy; however, perfect continence cannot be achieved because of loss of sensitivity. This study was designed in dogs to determine whether monitoring of rectal electric impedance can give information about fullness or motility of the rectum. METHODS: Four adult female beagle dogs underwent rectal electric impedance measurements using a bipolar electrode implanted on the rectal wall. An alternating current of 1 microA at a frequency of 4 kHz was applied between the two wires. Variations of impedance (called impedance waves), defecations, and weight of stools were recorded and analyzed. RESULTS: The basal rectal impedance was 682+/-19 omega. During the period of observation (n = 4), 84 impedance waves (amplitude, 72+/-2 omega; duration, 58+/-11 minutes) were observed and 33 defecations (weight of stools, 74+/-6 g) occurred. Four types of impedance waves were identified and classified into two groups: low-amplitude or short-duration waves (Types I, II, and III), and high-amplitude and long-duration waves (Type IV). Frequency of defecation was associated with the amplitude of the waves. The weight of stools was correlated with the duration of the waves (r = 0.574, n = 27, P = 0.002). Types I, II, and III waves were correlated with eventual partial defecations, whereas Type IV waves were correlated with complete defecations. After defecation, no spontaneous new defecation occurred before recovering at least 80 percent of the basal impedance. CONCLUSIONS: Rectal impedance variations are correlated with defecation in a canine model, and single bipolar measurements provide a suitable evaluation of rectum fullness. This suggests the possible use of impedance signals to control electrostimulated graciloplasty after anorectal reconstruction.

Effects of short term sacral nerve stimulation on anal and rectal function in patients with anal incontinence.

BACKGROUND: Some patients with faecal incontinence are not amenable to simple surgical sphincter repair, due to sphincter weakness in the absence of a structural defect. AIMS: To evaluate the efficacy and possible mode of action of short term stimulation of sacral nerves in patients with faecal incontinence and a structurally intact external anal sphincter. PATIENTS: Twelve patients with faecal incontinence for solid or liquid stool at least once per week. METHODS: A stimulating electrode was placed (percutaneously in 10 patients, operatively in two) into the S3 or S4 foramen. The electrode was left in situ for a minimum of one week with chronic stimulation. RESULTS: Evaluable results were obtained in nine patients, with early electrode displacement in the other three. Incontinence ceased in seven of nine patients and improved notably in one; one patient with previous imperforate anus and sacral agenesis had no symptomatic response. Stimulation seemed to enhance maximum squeeze pressure but did not alter resting pressure. The rectum became less sensitive to distension with no change in rectal compliance. Ambulatory studies showed a possible reduction in rectal contractile activity and diminished episodes of spontaneous anal relaxation. CONCLUSIONS: Short term sacral nerve stimulation notably decreases episodes of faecal incontinence. The effect may be mediated via facilitation of striated sphincter muscle function, and via neuromodulation of sacral reflexes which regulate rectal sensitivity and contractility, and anal motility.

Tissue reactions to bacteria-challenged implantable leads with enhanced infection resistance.

Tissue reactions to implantable pacemaker leads were investigated in an early infection model in rabbits. Both standard leads and surface-modified leads were used. The surface modification technique was applied to achieve controlled release of the antibiotic gentamicin. The insulating polyurethane tubing material of the leads was provided with an acrylic acid/acrylamide copolymer surface graft and then loaded with gentamicin. Implantation periods varied from day 4, to week 3 1/2, to week 10. We investigated tissue reactions in the absence of an infectious challenge and also the efficacy of surface-modified leads in preventing infection after challenge with Staphylococcus aureus was evaluated. It was demonstrated that the applied surface modification did not induce adverse effects although during early postimplantation an increase in infiltration of granulocytes and macrophages and wound fluid and fibrin deposition were observed. After bacterial challenge, standard leads were heavily infected at each explantation period, denoted by abscesses, cellular debris, and bacterial colonies. In contrast, little or no infection was observed, either macroscopically or by bacterial cultures, with the surface-modified leads. Microscopy showed little evidence of the bacterial challenge, and that primarily at day 4. It was concluded that the applied surface modification demonstrated enhanced infection resistance and thus represents a sound approach to the battle against infectious complications with biomaterials.

Vascular and stimulation delays in dynamic musculoplasty.

BACKGROUND: Dynamic musculoplasty is increasingly being used to replace severely damaged muscle. Electrical stimulation induces a change in muscle composition from type II to type I muscle fibers. The aim of this study was to assess the optimal time to start stimulation and the beneficial effect of a vascular delay. METHODS: Both gracilis muscles in rabbits (n = 3 x 6) were wrapped around a double polyurethane tube, and leads were implanted together with a neurostimulator. Right muscles were electrically stimulated for 11 weeks, and left muscles served as controls. In group 1 the muscle was stimulated immediately after transposition, in group 2 it was stimulated after 6 weeks, and in group 3 a vascular delay was performed and stimulation was started immediately after transposition. RESULTS: During stimulation the percentage of type 1 muscle fibers increased from a mean of 4.6% to 41.9%. In group 1 there was significantly more change in muscle tissue. There were no significant differences in recorded pressures between groups. In group 1 the increase in amplitude during stimulation was significantly elevated (p < 0.05). The fatigue index in group 1, 259 (SE 130) seconds, was significantly lower than that of group 2, 515 (SE 102) seconds (p < 0.05). CONCLUSIONS: Compared with the methods used in groups 2 and 3, immediate stimulation (group 1) gives more change in muscle tissue, demanding a higher increase in amplitude to achieve sufficient contraction. The fatigue index is also impaired. Thus vascular delay, as presently applied, does not improve muscle function.

Gastrointestinal transit and prolonged ambulatory colonic motility in health and faecal incontinence.

BACKGROUND: Colonic motor function has not been studied in the ambulatory setting over a prolonged period in the unprepared state. Furthermore, the disturbance of this function in patients with faecal incontinence is unknown. AIM: To study colonic function over two to three days in the ambulatory, unprepared state in health and in patients with idiopathic faecal incontinence. METHODS: Six healthy women and six women with faecal incontinence and a structurally intact anal sphincter ingested a dual radioisotope meal, and had a six sensor, solid state manometric probe colonoscopically inserted into the left colon. Scanning was performed until radioisotope left the gut and pressure was recorded for a median of 44 hours. RESULTS: Three of six patients showed abnormal gastric emptying. Patients showed no disturbance of colonic radioisotope transit. Controls had a median of 12, whereas patients had a median of 16, high amplitude propagated waves per 24 hours. In three patients urge incontinence was associated with high amplitude (up to 500 cm water) propagated waves which often reached the rectum. These high pressure waves were identical to those occurring in healthy subjects, the only difference being the lack of adequate sphincter response. Passive incontinence was not associated with colonic motor activity. Defaecation in all subjects was associated with identical propagated waves, and distal movement of 13% (median) of right colonic content and excretion of 32% from the left colon and rectum. The urge to defaecate was associated with either propagated waves (45%) or non-propagated contractions (55%). Rectal motor complexes were recorded in both groups of subjects, but similar rhythmic activity was also recorded in the sigmoid and descending colon. CONCLUSIONS: Normal colonic function consists of frequent high pressure propagated waves. Rhythmic activity occurs both proximal to and in the rectum. Defaecation is characterised by high pressure propagated waves associated with coordinated anal sphincter relaxation. Patients with faecal incontinence may have a widespread disturbance of gut function. Urge incontinence, an urge to defaecate, and defaecation can all be associated with identical high amplitude propagated pressure waves.

Dynamic myoplasty: surgical transfer and stimulation of skeletal muscle for functional substitution or enhancement.

Dynamic myoplasty combines muscle transfer with electrical stimulation to provide contractile function that augments or replaces impaired organ function. Dynamic cardiomyoplasty was the first clinical application in which a skeletal muscle, latissimus dorsi, was transferred and stimulated to provide cardiac assistance, a function different from its original one. The problem of early muscle fatigue that was encountered in the initial implementation of the method was solved by training the muscle with electrical stimulation and thus changing its fiber composition. With intramuscular electrodes, the conditioned latissimus dorsi is stimulated in synchrony with the heart muscle. Safeguards are built into the two-channel implanted stimulator to avoid excessively high pulse rates. Clinicians report that 80% of patients with moderate to severe heart failure prior to operation showed a clinical improvement of 1.6 New York Heart Association classes. Alternative methods of providing cardiac assistance that are also being investigated include wrapping the muscle around the aorta, creating a skeletal muscle ventricle, and using the muscle to power an implantable pump. These latter techniques are still under preclinical investigation. Compared with heart transplant, cardiomyoplasty has the great advantage of not being subject to tissue rejection. The second principal application of dynamic myoplasty is treatment of fecal incontinence through creation of an electrically stimulated skeletal muscle neosphincter (ESMNS). The gracilis muscle of the leg is mobilized, wrapped around the anal canal, and conditioned with electrical stimulation to become more fatigue resistant. To achieve continence, the muscle is continuously stimulated except when the patient wishes to defecate. Overall success rates in achieving continence are 60-65%. Both cardiomyoplasty and the ESMNS technique, and their associated devices, are being refined through ongoing clinical trials.

Technology transfer of neuroprosthetic devices.

Despite long development periods for neuroprosthetic devices, the numbers in clinical use or clinical trials are rising, with an estimated 3,000 systems in use today. As they gain experience with the regulatory approval process, developers are learning to conduct research to best prepare for transfer of technology to industry. The track record of the first motor prosthesis to be approved by the United States Food and Drug Administration contains important lessons for a company planning to undergo the regulatory process. Throughout the development of a neuroprosthesis, the capabilities and preferences of the customers who will use it (physicians, surgeons, therapists, and end-users) should be sought out and used in device design. When a device has reached clinical application, particular attention is needed to maximize both the population who will use it and each individual's degree of use (optimal, partial, reluctant). Identification of person-technology mismatches can help to select training strategies and other interventions that can be applied to ensure a good rehabilitation outcome.