Sacral Anterior Root Stimulation Research Articles

Invasive carcinoma of urinary bladder in a patient with a spinal cord injury with non-functioning Brindley sacral anterior root stimulator: a case report

BackgroundAnterior sacral root stimulation combined with sacral posterior rhizotomy restores bladder function in spinal cord-injured patients suffering from hyperactive bladder. After successful implantation of bladder stimulator, urinary infection rate decreases, and patients are able to get rid of indwelling urinary catheters, which in turn reduce the risks for vesical malignancy. We present a spinal cord injury patient with non-functioning Brindley sacral anterior root stimulator, who developed carcinoma of urinary bladder.Case presentationA Caucasian male, who was born in 1943, sustained paraplegia at T-4 (ASIA-B) in 1981. This patient underwent implantation of sacral anterior root stimulator in September 1985. The bladder stimulator started giving trouble since 1996 and the patient went back to using indwelling urethral catheter. In August 2006, this patient passed blood in urine after a routine change of indwelling catheter. Cystoscopy showed unhealthy bladder mucosa. Bladder biopsy revealed carcinoma, which was infiltrating bundles of muscularis propria. Many of the nests showed evidence of squamous differentiation, while others could be transitional or squamous. This patient underwent cystectomy with lymphadenectomy in March 2007 in a hospital nearer his home. Histology showed three nodes involved. This patient has been doing well since the operation.ConclusionOccurrence of vesical malignancy in this patient with non-functioning bladder stimulator is a timely reminder to all health professionals, and health care managers that concerted efforts should be made to rectify a non-functioning sacral anterior root stimulator as soon as possible. Otherwise, facilities should be made available in the community for the spinal cord injury patient to use intermittent catheterisation and thereby, avoid permanent indwelling catheter, vesical calculi and urine infections, which are risk factors for bladder cancer.

Optimal treatment for severe neurogenic bowel dysfunction after chronic spinal cord injury: a decision analysis

When conservative management fails in patients with chronic spinal cord injury (SCI) and neurogenic bowel dysfunction, clinicians have to choose from a variety of treatment options which include colostomy, ileostomy, Malone anterograde continence enema (MACE) and sacral anterior root stimulator (SARS) implantation. This study employed a decision analysis to examine the optimal treatment for bowel management of young individuals with chronic refractory constipation in the setting of chronic SCI. A decision analysis was created to compare the four surgical strategies using baseline analysis, one-way and two-way sensitivity analyses, 'worst scenario' and 'best scenario' sensitivity analyses, and probabilistic sensitivity analyses. Quality-adjusted life expectancy (QALE) was the primary outcome. The baseline analysis indicated that patients who underwent the MACE procedure had the highest QALE value compared with the other interventions. Sensitivity analyses showed that these results were robust. The MACE procedure may provide the best long-term outcome in terms of the probability of improving bowel function, reducing complication rates and the incidence of autonomic dysreflexia, and being congruent with patients' preferences. The analysis was sensitive to changes in assumptions about quality of life/utility, and thus the results could change if more specific estimates of utility became available.

A standardised mini pig model for in vivo investigations of anticholinergic effects on bladder function and salivation

Purpose The objective was to validate an in vivo model for evaluation of pharmacological effects on bladder function taking the most predominant anticholinergic side effect (hyposalivation) into account. Therefore, two anticholinergic properties (propiverine hydrochloride and tolterodine- l(+)-tartrate) were used to test the in vivo model. Sacral anterior root stimulation (SARS) was performed to induce reproducible and standardized bladder contractions. To evaluate hyposalivation standardised salivavary flow measurements by stimulating the lingual nerve was performed in addition to SARS. Materials and methods 10 male mini pigs were anaesthetised. The carotid artery was cannulated for blood pressure measurement and the jugular vein for administration of propiverine 0.4 mg kg −1 b.w. and tolterodine 0.06 mg kg −1 b.w. For stimulation-induced salivary flow measurements both lingual nerves were exposed and a cuff electrode was placed around the nerves. The bladder was exposed and a cystostomy catheter was inserted to performed cystometrographic measurements during SARS. Results In all experiments, for each animal reproducible intravesical pressure values (pves) and salivary flow rates were elicited during electrostimulation before administration of the drug. Bladder pressure: After administration of propiverine, neurostimulation-induced rise in pves had fallen by 60% from the initial value. After administration of tolterodine pves had fallen by about 50%. After additional administration of atropine pves decreased to about 15% of the initial value for both drugs. Salivation: After propiverine salivary flow had fallen by 61%. Inhibition of salivary flow under tolterodine was about 56%. Additional administration of atropine led in both drugs to a nearly complete blockade of salivation. Heart rate (HR) and blood pressure (BP): Directly following intravenous administration of both drugs, a short-term and reversible period of mild but significant fluctuations in HR was observed. There was also a slight but non-significant rise in blood pressure. Conclusions This model allows comparative investigations of various drugs with bladder inhibitory properties in terms of acute efficacy and side effects.

Refractory neurogenic detrusor overactivity

Refractory neurogenic detrusor overactivity refers to the clinical condition that is no longer manageable by anticholinergic therapy. This condition represents a formidable task to caregivers because the treatment of urinary incontinence and adequate protection of the upper urinary tract become extremely difficult. Treatment options for refractory neurogenic detrusor overactivity include detrusor injections of botulinum toxin and intravesical instillation of vanilloid compounds, mainly resiniferatoxin, or anticholinergic drugs. If these options fail, bladder augmentation or sacral anterior root stimulation offers excellent outcomes, although at much higher costs and risks to the patients.

Spastic Bladder and Spinal Cord Injury: Seventeen Years of Experience with Sacral Deafferentation and Implantation of an Anterior Root Stimulator

Artif Organs, 29: 239 -241, 2005 Introduction: Spinal cord injured patients with a suprasacral lesion usually develop a spastic bladder. The hyperreflexia of the detrusor and the external sphincter causes incontinence and threatens those patients with recurrent urinary tract infections (UTI), renal failure, and autonomic dysreflexia. All of these severe disturbances may be well managed by sacral deafferentation (SDAF) and implantation of an anterior root stimulator. Material and Method: Between September 1986 to December 2002, 464 paraplegic patients (220 female, 244 male) received a SDAF-SARS. Almost exclusively the SDAF was done intradurally, which means with one operation field there can be done two steps (SDAF and SARS). Results: 440 patients have a follow-up with 6.6 years (at least 6 months-17 years) The complete deafferentation was successful in 94.1%. A total of 420 paraplegics may use the SARS for voiding (frequency 4.7 per day) and 401 use it for defecation (frequency 4.9 per week). Continence was achieved in 364 patients (83%). UTI declined from 6.3 per year preoperatively to 1.2 per year postoperatively. Kidney function presented stable. Early complica- tions were 6 CSF leaks, 5 implant infections. Late complications with receiver or cable failures made us do surgical repairs in 34 paraplegics. A step-by-step program for trouble-shooting differentiates implant failure and myogenic or neurogenic failure. Conclusion: SDAF is able to restore the reservoir function of the urinary bladder and to achieve continence. Autonomic dysreflexia disappeared in most of the cases. By means of an accurate adjustment of stimulation parameters it is possible to accomplish low resistance micturition. The microsurgical technique requires an education. One has to be able to manage late implant complications. Editorial Comment: This is a very extensive and most impressive experience with a technique that is confined in usage to a very few centers. Perhaps this is because of the intensive education that the authors state is required in the microsurgical technique. In addition to what is described in the abstract, the following data from the short, sparsely referenced article are relevant: 1) 8 patients required a second deafferentation at the conus level to achieve a complete interruption of hyperreflexia; 2) in 22 of the 364 patients achieving continence the additional implantation of an artificial sphincter was required and 3) autonomic dysreflexia disappeared in all but 2 of 187 cases. The authors also state that implants with cable plugs could make repair procedures easier and the development of microelectronic devices without cables could help to avoid implant complications. The authors conclude by stating ...the satisfaction of our para- plegic patients with the outcome after SDAF and (sacral anterior root stimulation) is very high and they improve in independence and in quality of life. Sexual aspects are not considered in this article, but it can be assumed that reflex erections, where present, were lost with the complete transection of the afferent dorsal roots S2 to S5.

Long-term urological outcomes in paediatric spinal cord injury

Retrospective review. This retrospective review observes the evolution of bladder management by time and reports adult urological outcomes and complications in paediatric onset spinal cord injury (SCI). Spinal Injuries Unit RNOH Stanmore. In total, 10 traumatic SCI patients with mean age at injury of 13.6 years underwent treatment, for a mean period of 13.1 years. Characteristics of injury were noted. Two diagnostic subgroups, neurogenic detrusor overactivity (NDO), and acontractile detrusor were made. Complications, treatment changes, operative procedures with follow-up were noted. In group 1 (6/10 patients) with NDO, five had DSD. Initial bladder management was reflex/urge voiding (n=4), suprapubic catheterisation (SPC), (n=1) and self-intermittent catheterisation (SIC), (n=1). Two patients had multiple upper tract complications with decreased renal function, two recurrent symptomatic urinary infections and one; bladder calculus. In total, 12 operative procedures were performed to treat complications and change bladder management to, SIC+oxybutynin (n=3), ileal conduit (n=1), sacral anterior root stimulator implant (SARSI), (n=1), voiding on urge (n=1). In group 2 (4/10 patients) with a-contractile detrusor two had low compliance. Initial bladder management was SIC (n=3) and voiding on urge/straining (n=1). Two patients converted from SIC to permanent catheter drainage and reported complications. Incidental kidney stone was diagnosed in one. A total of four interventions were carried out with final management of SIC (n=2), voiding on urge/straining (n=1) and Mitrofanoff+ileocystoplasty (n=1). Bladder management in paediatric SCI is dependent on neurological level and type of injury; it changes with growth and is affected by changes in bladder management.

Endothelin‐A‐receptor antagonist LU 302146 inhibits electrostimulation‐induced bladder contractions in vivo

Endothelin (ET) is a strong constrictor of smooth muscle structures. The relevance of Endothelin-A receptors in the bladder was demonstrated in several in vitro studies. The aim of this functional study was to evaluate the acute effect of the selective ET-A-antagonist LU 302146 (LU) on neurostimulation-induced bladder contractions in vivo. Eight male mini pigs were anesthesized. The bladder was exposed and a double lumen catheter was inserted to perform intravesical pressure (pves) measurements. Laminectomy was performed for sacral anterior root stimulation (SARS) of S2. Four animals received the selective ET-A-antagonist LU, three atropine and one animal was treated with vehicle. Pves was recorded before and after drug administration as well as before and during neurostimulation. At the end of each LU trial, a supplementary application of 4 mg atropine was administered followed by a final SARS. In all experiments reproducible pves values were elicited during electrostimulation before administration of the test substance. The selective ET-A-antagonist reduced stimulation-induced bladder contraction by a mean of 57%. Additional administration of atropine inhibited the detrusor contraction almost completely during SARS. The vehicle had no effect on bladder contraction. In the presented animal model, ET-1 inhibition with the selective ET receptor-A-antagonist LU 302146 decreases stimulation-induced bladder contraction in vivo. The results suggest that the selective ET-A antagonist LU acts on the atropine-resistant component of efferent detrusor activation since additional administration of atropine almost completely abolish detrusor contraction. This observation in addition to the involvement of ET-1 in bladder smooth muscle proliferation, raises the possibility that ET-receptor antagonists might be beneficial in patients with neurogenic bladder dysfunction or in patients with functional or anatomical BOO.

Interface pressure and cutaneous hemoglobin and oxygenation changes under ischial tuberosities during sacral nerve root stimulation in spinal cord injury

Noninvasive functional magnetic stimulation (FMS) of the sacral nerve roots can activate gluteal muscles. We propose the use of sacral anterior root stimulator (SARS) implants to prevent ischial pressure ulcers in the spinal cord injury (SCI) population. In this study, we (1) investigated the acute effects of sacral FMS on ischial pressure, skin blood content, and oxygenation changes in people with SCI and demonstrated the utility of FMS as an assessment tool, and (2) showed that similar effects are possible with electrical stimulation via a SARS implant. Results indicated that sacral nerve root stimulation, either by FMS or implanted electrical stimulation, induced sufficient gluteus maximus contraction to significantly change subjects' ischial pressures and cutaneous hemoglobin and oxygenation during sitting. In addition to these beneficial acute effects, chronic stimulation via a SARS implant may build gluteal muscle bulk and prevent or reduce pressure ulcers in the SCI population.

Pressure changes under the ischial tuberosities of seated individuals during sacral nerve root stimulation

Neuromuscular stimulation via the sacral nerve roots is proposed for prevention of ischial pressure ulcers following a spinal cord injury (SCI). Acute effects of sacral functional magnetic stimulation (FMS) on seat interface pressure changes were investigated in five nondisabled volunteers. Similar effects were demonstrated with functional electrical stimulation in people with SCI who used a sacral anterior root stimulator implant. The results indicated that sacral nerve root stimulation, either by FMS or implanted electrical stimulation, induced gluteus maximus contraction and mild pelvic tilt sufficient for clinically significant reductions in ischial pressures during sitting.

Differential effects of sacral anterior root stimulation on anal sphincter and colorectal motility in spinally injured man.

The motility responses of the sigmoid colon, rectum and external anal sphincter to sequential electrical stimulation of the anterior sacral roots (S2, S3 and S4) were studied in five patients with traumatic spinal cord injury. Identical and reproducible results were obtained. S2 stimulation provoked isolated low-pressure colorectal contractions. S3 stimulation initiated high-pressure colorectal motor activity which appeared peristaltic and was enhanced with repetitive stimuli. This response appeared to be frequency-dependent. S4 stimulation increased colonic and rectal tone. External sphincter activity was stimulated in increasing order from S2 to S4. These observations directly elucidate the central control of colorectal motility and may have implications in the treatment of severe constipation following spinal injury.

Deafferentation of the Urinary Bladder and Implantation of a Sacral Anterior Root Stimulator (SARS) for Treatment of the Neurogenic Bladder in Paraplegic Patients

Deafferentation of the Urinary Bladder and Implantation of a Sacral Anterior Root Stimulator (SARS) for Treatment of the Neurogenic Bladder in Paraplegic Patients

Treatment of Overactive Bladder

The lower urinary tract has two main functions: storage and periodic elimination of urine. These two functions are regulated by a complex neural control system involving a central pathway located in the spinal cord, pons and brain as well as by the peripheral autonomic and somatic neural pathways. Vesico-urethral dysfunction is a major problem in daily medical practice. Detrusor overactivity is characterized by involuntary detrusor contractions during the filling phase of a cystometrogram. But the definition is sometimes a symptom syndrome suggestive of lower urinary tract dysfunction characterized by urgency, usually with increased daytime frequency and nocturia. Neurogenic and idiopathic overactive bladder must be differentiated. In the case of a low risk for an upper urinary tract, conservative therapies are primarily discussed, and current pharmacological treatment involving the use of muscarinic receptor antagonists. Vanilloids drugs and botulinum toxin have shown promising results, but further injections may be required with repetitive catheterization. To restore retention (continence) and emptying (micturition), surgical techniques intervening in the peripheral or central nervous systems have always played an important role. Functional surgery such as the Brindley technique (anterior sacral root stimulation with posterior rhizotomy) is still the only technique for restoring bladder function, continence, and micturition. It is especially useful for patients with an overactive bladder, suffering from a complete spinal cord lesion. Sacral neuromodulation (sacral root stimulation with a low-frequency current) is indicated for idiopathic overactivity and sometimes for incomplete spinal lesions.

Methylene blue staining for nerve-sparing operative procedures: an animal model

Objectives To evaluate methylene blue fiber staining as a method of nerve fiber identification in an animal model, because the maintenance of organ function after surgery depends on exact intraoperative identification of the relevant nerve fibers. Methods Brindley electrodes were implanted bilaterally at S3 for sacral anterior root stimulation in six minipigs. For reference, stimulation-induced detrusor contractions were recorded urodynamically. After exposure of the ureterovesical junction on both sides, a 2:8 methylene blue solution was applied to the right side; the left side remained untreated. Bilateral dissection of the ureter from the surrounding tissue for a distance of 4 cm proximal to the ureterovesical junction was performed. The methylene blue-stained nerve fibers on the right side were spared; no particular attention was paid to the nerves on the left. Again, sacral anterior root stimulation-induced detrusor contractions were monitored urodynamically on both sides. Then, the identified nerve fibers on the right were cut intentionally, and the detrusor pressure was recorded again under stimulation. Finally, the dissected nerve structures were evaluated histologically. Results The reference bladder pressures after unilateral stimulation on the left side before ureter dissection showed a mean detrusor pressure (Pdet) of 19 cm H 2O. On the right side, the Pdet was 18 cm H 2O. After preparation on both sides, a mean Pdet of 3 cm H 2O was recorded after left side stimulation, and a Pdet of 17 cm H 2O after right side stimulation. When the stained nerve fibers on the right side were cut, no bladder contractions could be induced. The histomorphology of the stained and dissected structures revealed multiple autonomous nerve fibers and small vessels in connective tissue. Conclusions The identification of minute nerve bundles is a tedious and difficult task. The results from our animal model demonstrated that supravital staining of autonomous nerve fibers with methylene blue is a simple and reliable method of identification.

A 7-year follow-up of sacral anterior root stimulation for bladder control in patients with a spinal cord injury: quality of life and users' experiences.

Cross-sectional descriptive study. To assess long-term effects and quality of life (QoL) of using sacral anterior root stimulation (SARS) in spinal cord injured patients. Neurosurgical and Urological Departments of a large teaching hospital and a large rehabilitation centre in the Netherlands. In all, 42 patients with complete spinal cord injury (SCI) implanted between 1987 and 2000 were included. A questionnaire was constructed to determine complications, technical failures and personal experiences of the patients. The Qualiveen questionnaire was used and the outcome was compared with data obtained from a reference group of 400 SCI patients with neurogenic bladder problems not using the bladder controller. The Qualiveen questionnaire measures disease-specific aspects in four domains with respect to limitations, constraints, fears and feelings and general QoL aspects, suitable for use in SCI patients with urinary disorders. The results of 37 patients are presented. Our results with the bladder controller with respect to medical and technical complications and infection rates are similar to the results presented by others. From users' experiences, the most important advantages reported were a decreased infection rate (68%), improved social life (54%) and continence (54%). Comparison of the obtained results of our patient group with the Qualiveen questionnaire with a reference group not using the bladder controller indicates that the specific impact of urinary disorders in the four domains on QoL is reduced and that general QoL is improved. SARS is effective and safe for neurogenic bladder management in patients with complete SCI. Users' experiences are positive. Furthermore, this therapy seems to reduce the effects of urinary-disorder-specific QoL aspects, and to increase the QoL in general.

Dorsal Rhizotomy with Anterior Sacral Root Stimulation for Neurogenic Bladder

A spinal cord lesion above the sacral micturition center results in a loss of voluntary control and development of bladder sphincter dysynergia with hyperreflexia of the detrusor and spasticity of the sphincter. Sacral rhizotomy and implantation of an anterior sacral root stimulator appears as an effective method for the treatment not only of voiding dysfunction but also of defecation and sexual disturbance. The surgical technique is described as are the clinical and electrophysiological controls. The results of our series of operated patients with intradural implantation and sacral deaffentation show a constant improvement. 90% have satisfactory continence and no longer require an incontinence appliance. Bladder capacity and compliance have increased to 120% and urethral closure pressure has decreased. 80% have complete voiding or a post-void residue of not more than 50 ml. So, urinary infection rate is dramatically decreased.

Electrical stimulation for the treatment of bladder dysfunction: Current status and future possibilities

Electrical stimulation of peripheral nerves can be used to cause muscle contraction, to activate reflexes, and to modulate some functions of the central nervous system (neuromodulation). If applied to the spinal cord or nerves controlling the lower urinary tract, electrical stimulation can produce bladder or sphincter contraction, produce micturition, and can be applied as a medical treatment in cases of incontinence and urinary retention. This article first reviews the history of electrical stimulation applied for treatment of bladder dysfunction and then focuses on the implantable Finetech-Brindley stimulator to produce bladder emptying, and on external and implantable neuromodulation systems for treatment of incontinence. We conclude by summarizing some recent research efforts including: (a) combined sacral posterior and anterior sacral root stimulator implant (SPARSI), (b) selective stimulation of nerve fibers for selective detrusor activation by sacral ventral root stimulation, (c) microstimulation of the spinal cord, and (d) a newly proposed closed-loop bladder neuroprosthesis to treat incontinence caused by bladder overactivity. [Neurol Res 2002; 24: 413-430]

Passive Biaxial Mechanical Properties of the Rat Bladder Wall After Spinal Cord Injury

Changes in the mechanical properties of the bladder wall after spinal cord injury can alter bladder compliance and wall tension, leading to changes in afferent nerve activity and to abnormal reflex mechanisms. To our knowledge we report the first application of biaxial mechanical testing to the normal bladder wall and demonstrate how these properties change after spinal cord injury. Whole bladders were harvested from mature female Sprague-Dawley rats weighing 250 to 300 gm. Test group animals underwent complete spinal cord transection at the T9 to T10 level and normal animals comprised the control group. The bladders were cut open longitudinally, the trigone and apex were removed and the remaining tissue was trimmed to a square of 9 to 13 mm. per side. Mechanical properties of the tissue sample were tested using planar biaxial testing, in which a stress was applied in the circumferential and longitudinal (base-apex) directions, and resulting axial strains were measured. In normal and spinal cord injured rats bladder wall tissue demonstrated isotropic mechanical behavior when equal stress levels were applied in anatomical directions. However, under nonequi-biaxial loading bladder specimens were not truly isotropic but displayed anisotropic-like behavior. Spinal cord injured tissues were consistently more compliant than normal controls. Biaxial mechanical testing can detect differences in normal control and hypertrophied rat bladders 10 and 14 days after spinal cord injury. These changes represent an important component of the bladder response to spinal cord injury.

Selective block of urethral sphincter contraction using a modified Brindley electrode in sacral anterior root stimulation of the dog.

Patients with spinal cord injury often present with dysfunction of urinary bladder and urethral sphincter. One treatment option is sacral rhizotomy and sacral anterior root stimulation with the Finetech Brindley stimulator. However, a major disadvantage is the lack of selective stimulation, resulting in simultaneous contraction of sphincter and bladder followed by unphysiological micturition. This study investigated the possibility of selective bladder stimulation by using a Brindley electrode. In 11 male anaesthetized foxhounds, a complete posterior rhizotomy was perormed. The anterior S2 roots were stimulated with different quasi-trapezoidal (QT) pulses (pulse length range, 600-1,400 microsec; stimulation current, 0.1-2.0 mA; frequency, 20 Hz) by using a tripolar Brindley electrode. Sphincter and bladder pressures were measured urodynamically. All 11 animals showed a maximal reduction of the highest sphincter pressure over 80%, and in 6 of 11 trials, the sphincter pressure was inhibited completely (100%). With stimulations at maximal sphincter blockade, the average achievable bladder pressure was 33.48 cm H(2)O higher than the average sphincter pressure, and in three cases, a strong micturition was observed. Selective blockade of the sphincter was possible by applying QT pulses. The bladders remained uninfluenced by this blockade and kept their excitability at any time. This study shows that selective bladder stimulation with little or no coactivation of the sphincter is possible. A physiological micturition can be achieved by using a tripolar Brindley electrode. Introduction of this stimulation technique into clinical practice should not face major difficulties, considering that the device is an established electrode.

Physiologic bladder evacuation with selective sacral root stimulation: sinusoidal signal and organ-specific frequency.

In patients with spinal cord injury above S2, who characteristically have both detrusor hyperflexia and sphincteric spasm, sacral anterior root stimulation can evacuate the bladder, but sacral deafferentation is needed to eliminate the hyperreflexia for normal bladder filling. The common stimulation parameters for these patients activate the detrusor and the external urethral sphincter simultaneously (detrusor-sphincter dyssynergia), and the resultant post-stimulus voiding is not physiologic. We sought to determine organ-specific stimulation parameters. In 20 male dogs, the rectangular pulse and sinusoidal signal forms were evaluated with a variety of parameters for stimulation of S2 and S3 anterior roots extra- and intradurally (i.e., stimulation frequency and voltage, uni- versus bilateral electrode placement, and degree of bladder filling). New torpedo-shaped bipolar electrodes were used, adjusted to neural diameter. The best results were recorded with intradural bilateral sinusoidal signal. Sphincteric fatigue was produced by pre-stimulating S2 with 104+/-17 Hz and 0.8+/-0.1 V for 10 to 15 seconds before S3 stimulation. S3 stimulation with 16+/- 2.1 Hz and 0.4+/-0.1 V evoked a detrusor pressure of 28.7+/-3.0 cm H2O above the sphincteric pressure. Selective anterior root stimulation with organ-specific stimulation parameters can effect initial sphincteric fatigue to achieve physiologic voiding.

Selective suppression of sphincter activation during sacral anterior nerve root stimulation.

The purpose of this work was to electrically activate small-diameter motor fibers in the sacral anterior roots innervating the urinary bladder, without activating the large-diameter fibers to the sphincter. Quasitrapezoidal current pulses were applied through tripolar spiral nerve electrodes on selected anterior sacral roots during acute experiments on eight dogs, maintained under pentobarbital anesthesia. Pressures were recorded from the bladder and sphincter with catheter-mounted gauges. Stimulation with biphasic quasitrapezoidal pulses showed decrease in sphincter recruitment with increasing pulse amplitudes. The minimum current amplitude that resulted in maximum sphincter suppression was used to stimulate the roots with trains of 20 Hz pulses, with 60 mL of saline filling the bladder. Pressures were also recorded when 100 micros rectangular pulse trains at 20 Hz, both continuous and intermittent, were applied. Trains of stimuli were applied before and after dorsal root rhizotomy. Suppression of sphincter activation was defined to be a percentage, [(Maximum pressure -Minimum pressure)/Maximum pressure x100. The results from 22 roots in eight animals show that with single pulses, the average percentage suppression of sphincter activation was 76.3% (+/-14.0). The minimum current for maximum sphincter suppression was 1.29 mA (+/-0.62). The average bladder pressure evoked was 50 cm of water during pulse train stimulation, with no significant difference due to pulse type. With pulse trains, the sphincter pressures were significantly higher when the bladder was filled. Evacuation of fluid occurred in three animals with average flow rates of 1.0 mL/s.