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N J Rijkhoff

Publications and source records attributed to N J Rijkhoff.

15 recordsLinked to original sources
PubMed2001

An implant for chronic selective stimulation of nerves.

An implantable stimulator system has been developed for nerve stimulation. The system is capable of stimulating selectively, either by fibre position, fibre size or by sending action potentials in one direction only, based on the use of nerve cuffs. The stimulator produces either quasi-trapezoidal current pulses, to allow anodal blocking, or conventional rectangular-shaped current pulses, of amplitude 20 microA to 5 mA (in 20 microA steps) with duration of 16 micros to 1 ms (in 8 micros steps). For safety, both active and passive charge balancing is used. The amplitude of the active charge-balancing phase can be varied between 1/7 and 1/47 of the pulse amplitude. During manufacture, each implant is customised so as to drive either 6 quasi-tripolar (dipolar), 4 tripolar or 2 pentapolar cuffs. Possible applications of the device are: improved defaecation and bladder voiding after spinal cord injury, by stimulation of the sacral motor roots; neuromodulation to reduce hyperreflexia without concomitant muscle contractions; in stroke patients, to enable balanced inversion-eversion while dorsiflexing the ankle by stimulating the peroneal nerve. It may also be used in chronic animal experiments.This paper describes the implant system, its hardware and communication protocol, and shows results from in vitro tests of the device and the first acute anodal-blocking experiments in pigs.

Animals↗
PubMed2000

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.

Action Potentials↗
PubMed1998

A computer model of the neural control of the lower urinary tract.

Better understanding of the underlying working mechanism of the neural control of the lower urinary tract will facilitate the treatment of dysfunction with a neurogenic cause. We developed a computer model to study the effect of a neural control system on lower urinary tract behavior. To model the mechanical properties and neural control, assumptions had to be made. These assumptions were based, as much as possible, on knowledge and hypotheses taken from the literature. With valid assumptions, it should be possible to simulate normal as well as pathological behavior. To test the computer model, first, normal behavior of the lower urinary tract was simulated, and secondly, the known features of bladder outlet obstruction were simulated after the properties of the urethra were changed. The simulation results are comparable with measured data, so the assumptions on which the model is based could be valid. If the assumptions are valid, the feedback loops used in the model are also important feedback loops in vivo, and the model can be used to gain insight into the underlying mechanism of neural control.

Computer Simulation↗
PubMed1998

Selective detrusor activation by sacral ventral nerve-root stimulation: results of intraoperative testing in humans during implantation of a Finetech-Brindley system.

Electrical sacral nerve-root stimulation can be used to induce bladder contraction. However, bladder emptying is hampered by simultaneous contraction of the external urethral sphincter. Voiding may improve when using a stimulation method that allows selective detrusor activation. Both theoretical and animal studies have demonstrated that it is possible to obtain selective detrusor activation by sacral root stimulation using an selective anodal block. The objective of this paper is to demonstrate the feasibility of this stimulation method in humans. For investigation of the stimulation method, intraurethral and intravesical pressure responses to sacral root stimulation were measured in acute experiments on 12 patients. The results show that selective detrusor activation is possible in patients. Future perspectives are discussed.

Electric Stimulation↗
PubMed1997

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.

Electric Stimulation↗
PubMed1997

Selective detrusor activation by electrical stimulation of the human sacral nerve roots.

The purpose of this study was to investigate the feasibility of selective detrusor activation without activation of the urethral sphincter by sacral root stimulation in patients. The sacral roots were stimulated using a tripolar electrode. An anodal block was used to prevent the urethral sphincter from contraction. Using square current pulses (700 microseconds, 6-7 mA), no increase in intraurethral pressure was measured, while a normal increase in intravesical pressure occurred. The minimum pulse duration to obtain a complete block was 550 microseconds. The study shows that anodal blocking of action potentials is possible in humans and can result in selective detrusor activation when used in sacral root stimulation.

Action Potentials↗
PubMed1997

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.

Electric Stimulation Therapy↗
PubMed1996

Morphometric data of canine sacral nerve roots with reference to electrical sacral root stimulation.

Experiments to investigate restoration of lower urinary tract control by electrical stimulation of the sacral nerve roots are mostly performed on dogs, yet little morphometric data (such as canine root and fiber diameter distributions) are available. The aim of this study was to acquire morphometric data of the intradural canine sacral dorsal and ventral roots (S1-S3). Cross-sections of sacral roots of two beagle dogs were analyzed using a light microscope and image processing software. The cross-sectional area of each root was measured. The diameters of the fibers and the axons in the cross-sections of the S2 and S3 roots were measured and used to construct nerve fiber diameter frequency distribution histograms. The results show a unimodal diameter distribution for the dorsal roots and a bimodal distribution for the ventral roots. In addition the average ratio g of the axon diameter to fiber diameter was calculated for each root.

Animals↗
PubMed1995

Modelling selective activation of small myelinated nerve fibres using a monopolar point electrode.

The aim of this study is to investigate theoretically the possibility for activation of small myelinated nerve fibres without activating larger ones when stimulating a nerve fibre bundle using a monopolar point electrode. Therefore, the sensitivity of excitation and blocking threshold currents of nerve fibres to fibre diameter, electrode-fibre distance and pulse duration has been simulated by a computer model. A simple infinite, homogeneous volume conductor and a cathodal point source were used in combination with a model representing the electrical properties of a myelinated nerve fibre. The results show that selective activation of small myelinated fibres may be possible in a region at some distance from the electrode.

Computer Simulation↗
PubMed1994

Selective sacral root stimulation for bladder control: acute experiments in an animal model.

High bladder pressure is a potential side effect of poststimulus voiding, used to date for stimulation-induced bladder emptying in spinal cord injured patients. To prevent this side effect, selective activation of the bladder without activation of the urethral sphincter by selective stimulation of sacral roots was studied in a canine animal model. On-line registration of bladder, urethral and rectal pressure was performed, and EMG of tail muscles and urethral sphincter was recorded. After laminectomy, intradural left and right sacral root S2 were stimulated with a tripolar cuff electrode. A self-made stimulator generating adjustable pulse shapes was used. Using 200 microsec. rectangular pulses, contraction of bladder and urethral sphincter could be elicited. Selective activation of the bladder occurred with pulses of 600 to 800 microsec. due to anodal blocking of the large nerve fibers in the sacral roots. During acute animal experiments we were able to achieve selective activation of the detrusor without simultaneous activation of the external urethral sphincter, and complete, low-pressure voiding occurred.

Animals↗
PubMed1994

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 stimulated by a computer model. A 3-D 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.

Animals↗
PubMed1993

Reconstructing muscle activation during normal walking: a comparison of symbolic and connectionist machine learning techniques.

One symbolic (rule-based inductive learning) and one connectionist (neural network) machine learning technique were used to reconstruct muscle activation patterns from kinematic data measured during normal human walking at several speeds. The activation patterns (or desired outputs) consisted of surface electromyographic (EMG) signals from the semitendinosus and vastus medialis muscles. The inputs consisted of flexion and extension angles measured at the hip and knee of the ipsilateral leg, their first and second derivatives, and bilateral foot contact information. The training set consisted of data from six trials, at two different speeds. The testing set consisted of data from two additional trials (one at each speed), which were not in the training set. It was possible to reconstruct the muscular activation at both speeds using both techniques. Timing of the reconstructed signals was accurate. The integrated value of the activation bursts was less accurate. The neural network gave a continuous output, whereas the rule-based inductive learning rule tree gave a quantised activation level. The advantage of rule-based inductive learning was that the rules used were both explicit and comprehensible, whilst the rules used by the neural network were implicit within its structure and not easily comprehended. The neural network was able to reconstruct the activation patterns of both muscles from one network, whereas two separate rule sets were needed for the rule-based technique. It is concluded that machine learning techniques, in comparison to explicit inverse muscular skeletal models, show good promise in modelling nearly cyclic movements such as locomotion at varying walking speeds.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1992

Potential distribution and single-fibre action potentials in a radially bounded muscle model.

In modelling the electrical behaviour of muscle tissue, we used to employ a frequency-dependent volume conductor network model, which was infinitely extended in all directions. Equations in this model could be solved using a finite-difference approach. The most important restriction of this model was the fact that no boundary effects could be incorporated. Analytical models of muscle tissue normally do not have this disadvantage, but in those models the microscopic structure of muscle tissue cannot be taken into account. In the paper, we present a combined numerical/analytical approach, which enables the study of potential distributions and SFAPs in simulated microscopic muscle tissue in which the influence of the muscle boundary has been considered. We considered muscle models with radii of 1.5 mm and 10 mm. Both models were compared with an unbounded network model. In the model with a radius of 1.5 mm we varied the position of the active fibre relative to the muscle surface. It appeared that in most cases the presence of a boundary had a considerable effect on the potential distribution. An increase in the peak-to-peak value of the SFAP amplitude up to 300 per cent was noticed when the active fibre was positioned 500 microns beneath the muscle surface in a model with a radius of 1.5 mm.

Action Potentials↗
PubMed1991

Contact combinations in epidural spinal cord stimulation. A comparison by computer modeling.

The geometrical characteristics of longitudinal fiber populations in the dorsal columns (DC), recruited by various contact combinations in epidural spinal cord stimulation (SCS), were compared in a theoretical study. A 3-dimensional computer model was used, representing the geometry and electrical conductivity of the low-thoracic spinal cord and surrounding tissues, in combination with a model representing the electrical properties of a myelinated nerve fiber. It was calculated that, among usual dorsomedial contact combinations, the ratio of mediolateral and dorsoventral extent of the recruited area in DC only varied by 2-5%. The model predicts that in bipolar stimulation the relative lateral extent was smallest at a contact separation of 3-3.5 times the dorsal cerebrospinal-fluid width, which seems to fit the highest ratio of discomfort threshold/paresthesia threshold. It is concluded that the optimal combination varies with distance between cathode and DC and that a unique 'best contact combination' does not exist. When both a decrease of primary afferent diameter in DC and collateral branching near their entrance are considered, the model predicts that recruitment of cutaneous afferents will start in lateral DC and proceed medially at increasing stimulus, which fits clinical observations on the spread of paresthesia. The model predicts that large fibers in the posterior spinocerebellar tract will also be recruited in SCS.

Cerebrospinal Fluid↗