Nico Rijkhoff

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

Abstract 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]

URINARY BLADDER CONTROL BY ELECTRICAL STIMULATION : REVIEW OF ELECTRICAL STIMULATION TECHNIQUES IN SPINAL CORD INJURY

Evacuation of urine in paraplegics without the need for catheters would be possible when voiding could be induced by eliciting a bladder contraction. A challenging option to obtain detrusor contraction is electrical stimulation of the detrusor muscle or its motor nerves. This article reviews the 4 possible stimulation sites where stimulation would result in a detrusor contraction: the bladder wall, the pelvic nerves, the sacral roots, and the spinal cord. With respect to electrode application, sacral root stimulation is most attractive. However, in general, sacral root stimulation results in simultaneous activation of both the detrusor muscle and the urethral sphincter, leading to little or no voiding. Several methods are available to overcome the stimulation‐induced detrusor‐sphincter dyssynergia and allow urine evacuation. These methods, including poststimulus voiding, fatiguing of the sphincter, blocking pudendal nerve transmission, and selective stimulation techniques that allow selective detrusor activation by sacral root stimulation, are reviewed in this paper.

Selective stimulation of sacral nerve roots for bladder control: A study by computer modeling

The aim of this study was to investigate theoretically the conditions for the activation of the detrusor muscle without activation of the urethral sphincter and afferent fibers, when stimulating the related sacral roots, Therefore, the sensitivity of excitation and blocking thresholds of nerve fibers within a sacral root to geometric and electrical parameters in tripolar stimulation using a cuff electrode, have been simulated by a computer model. A 3D rotationally symmetrical model, representing the geometry and electrical conductivity of a nerve root surrounded by cerebrospinal fluid and a cuff was used, in combination with a model representing the electrical properties of a myelinated nerve fiber. The electric behavior of nerve fibers having different diameters and positions in a sacral root was analyzed and the optimal geometric and electrical parameters to be used for sacral root stimulation were determined. The model predicts that an asymmetrical tripolar cuff can generate unidirectional action potentials in small nerve fibers. While blocking the large fibers bidirectionally. This result shows that selective activation of the detrusor may be possible without activation of the urethral sphincter and the afferent fibers.<<ETX>>

Gastric transit and small intestinal transit time and motility assessed by a magnet tracking system

BackgroundTracking an ingested magnet by the Magnet Tracking System MTS-1 (Motilis, Lausanne, Switzerland) is an easy and minimally-invasive method to assess gastrointestinal transit. The aim was to test the validity of MTS-1 for assessment of gastric transit time and small intestinal transit time, and to illustrate transit patterns detected by the system.MethodsA small magnet was ingested and tracked by an external matrix of 16 magnetic field sensors (4 × 4) giving a position defined by 5 coordinates (position: x, y, z, and angle: θ, ϕ). Eight healthy subjects were each investigated three times: (1) with a small magnet mounted on a capsule endoscope (PillCam); (2) with the magnet alone and the small intestine in the fasting state; and (3) with the magnet alone and the small intestine in the postprandial state.ResultsExperiment (1) showed good agreement and no systematic differences between MTS-1 and capsule endoscopy when assessing gastric transit (median difference 1 min; range: 0-6 min) and small intestinal transit time (median difference 0.5 min; range: 0-52 min). Comparing experiments (1) and (2) there were no systematic differences in gastric transit or small intestinal transit when using the magnet-PillCam unit and the much smaller magnetic pill. In experiments (2) and (3), short bursts of very fast movements lasting less than 5% of the time accounted for more than half the distance covered during the first two hours in the small intestine, irrespective of whether the small intestine was in the fasting or postprandial state. The mean contraction frequency in the small intestine was significantly lower in the fasting state than in the postprandial state (9.90 min-1 vs. 10.53 min-1) (p = 0.03).ConclusionMTS-1 is reliable for determination of gastric transit and small intestinal transit time. It is possible to distinguish between the mean contraction frequency of small intestine in the fasting state and in the postprandial state.

Selective detrusor activation by electrical sacral nerve root stimulation in spinal cord injury

Electrical sacral nerve root stimulation can be used in spinal cord injury patients to induce urinary bladder contraction. However, existing stimulation methods activate simultaneously both the detrusor muscle and the urethral sphincter. Urine evacuation is therefore only possible using poststimulus voiding. Micturition would improve if the detrusor muscle could selectively be activated. The purpose of this study was to demonstrate selective detrusor activation in patients by ventral sacral root stimulation. The stimulation method involves selective activation of the small diameter myelinated nerve fibers and consists of a combination of cathodal excitation and selective anodal blocking using a tripolar electrode. To investigate anodal blocking, the intraurethral pressure response to stimulation was measured in acute experiments performed on 12 patients. The influence of both pulse amplitude and pulse duration on the pressure response was analyzed. In 8 out of 12 patients anodal blocking of somatic motor fibers was possible. This study also indicates the feasibility of selective detrusor activation by sacral root stimulation.

Acute animal studies on the use of an anodal block to reduce urethral resistance in sacral root stimulation

Electrical stimulation of sacral roots for electromicturition results in simultaneous activation of bladder and external urethral sphincter. The sphincter contraction hinders bladder emptying. Here, anodal blocking is described as a means to reduce the activation of the urethral sphincter. Using a tripolar electrode configuration and monophasic rectangular current pulses in acute canine experiments, a reduction of intraurethral pressure response, as compared to stimulation without blocking, of more than 80% could be achieved in all experiments. >

Neuroprostheses to treat neurogenic bladder dysfunction: current status and future perspectives

BackgroundNeural prostheses are a technology that uses electrical activation of the nervous system to restore function to individuals with neurological or sensory impairment.IntroductionThis article provides an introduction to neural prostheses and lists the most successful neural prostheses (in terms of implanted devices).Current treatmentThe article then focuses on neurogenic bladder dysfunction and describes two clinically available implantable neural prostheses for treatment of neurogenic bladder dysfunction. Special attention is given to the usage of these neural prostheses in children.Future treatmentFinally, three new developments that may lead to a new generation of implantable neural prostheses for bladder control are described. They may improve the neural prostheses currently available and expand further the population of patients who can benefit from a neural prosthesis.

ANALYSIS OF BLADDER RELATED NERVE CUFF ELECTRODE RECORDINGS FROM PREGANGLIONIC PELVIC NERVE AND SACRAL ROOTS IN PIGS

PURPOSE Electrical stimulation of appropriate lower urinary tract (LUT) nerves may be used in bladder dysfunction to achieve continence and abolish hyper-reflexic detrusor contractions. It can also be used for consequent emptying of the bladder. To control the time course of the described functional phases, knowledge of bladder sensory information is needed. We investigated if the latter could be extracted from the LUT nerve activity. MATERIALS AND METHODS In acute experiments using 10 pigs, tripolar cuff electrodes were placed unilaterally around the pelvic nerve and the S3 and S2 roots. The cuff electrode signals, filling rate and the bladder and rectal pressures were recorded during slow and fast bladder fillings/emptyings. RESULTS Two pigs were excluded from the analysis because of no observed changes in the nerve signals in one animal, and because of electrical noise problems in the other animal. Fast bladder pressure increases resulted in a sudden pelvic nerve signal rise in 6 out of 7 pigs (3 out of 6 for the S3 nerve signal). Slow bladder pressure increase was reflected in the recorded nerve activity only in 3 out of 8 and in 3 out of 7 pigs for the pelvic and S3 cuff signals respectively. In 2 animals small spontaneous bladder contractions were clearly reflected in the pelvic nerve signal (contractions were observed only in 3 pigs). Except in one pig, there were no slow/fast bladder filling responses recorded in the S2 roots. It is shown that the recorded responses were afferent. CONCLUSIONS Cuff electrodes can be used to record bladder afferent information from the pelvic nerve and the sacral root S3 in pig. Pelvic nerve recordings were more selective than the sacral root recordings. Nerve activity increases were more distinct and repeatable during rapid bladder pressure changes and small spontaneous bladder contractions than during slow bladder fillings.

Patient controlled versus automatic stimulation of pudendal nerve afferents to treat neurogenic detrusor overactivity.

PURPOSE We investigated whether patients with neurogenic detrusor overactivity can sense the onset of bladder contraction and in turn suppress the contraction by electrical stimulation of the dorsal penile-clitoral nerve. MATERIALS AND METHODS A total of 67 patients with different neurological disorders were recruited to undergo 3 filling cystometries. The first cystometry was done without stimulation. The second cystometry was performed with automatic controlled stimulation based on detrusor pressure. The third cystometry was done with patient controlled stimulation using a push button. RESULTS Four females and 13 males underwent all 3 fillings. Compared to cystometry 1 average bladder capacity for cystometries 2 and 3 was 60% higher. Compared to peak pressure for cystometry 1 average peak pressure during suppressed contractions for cystometries 2 and 3 was 49% and 26% lower, respectively. The average delay of the onset of stimulation during cystometry 3 with respect to cystometry 2 was 5.7 seconds. CONCLUSIONS The study shows that patient controlled genital nerve stimulation is as effective as automatic controlled stimulation to treat neurogenic detrusor overactivity. Thus, patient controlled stimulation is feasible in select patients, although patients must be trained in the technique.

Different pulse shapes to obtain small fiber selective activation by anodal blocking-a simulation study

The aim of this study was to investigate whether it is possible to reduce a charge per pulse, which is needed for selective nerve stimulation. Simulation is performed using a two-part simulation model: a volume conductor model to calculate the electrical potential distribution inside a tripolar cuff electrode and a human fiber model to simulate the fiber response to simulation. Selective stimulation is obtained by anodal block. To obtain anodal block of large fibers, long square pulses (>350 /spl mu/s) with a relatively high currents (1-2.5 mA) are usually required. These pulses might not be safe for a long-term application because of a high charge per pulse. In this study, several pulse shapes are proposed that have less charge per pulse compared with the conventional square pulse and would therefore be safer in a chronic application. Compared with the conventional square pulse, it was possible to reduce the charge with all proposed pulse shapes, but the best results are obtained with a combination of a square depolarizing pulse and a blocking pulse. The charge per pulse was up to 32% less with that pulse shape than with a square pulse. Using a hyperpolarizing anodal prepulse preceding a square pulse, it was not possible to block nerve fibers in a whole nerve bundle and to obtain reduction of a charge per phase. Reduction of the charge could be achieved only with spatially selective blocking. The charge per phase was larger for the combination of a hyperpolarizing anodal prepulse and a two-step pulse than for the two-step pulse alone.