A urethral afferent mediated excitatory bladder reflex exists in humans

Randomized Controlled Trial to Assess the Impact of Intraurethral Lidocaine on Urodynamic Voiding Parameters

OBJECTIVES

The aim of the study was to determine whether intraurethral anesthesia decreases voiding efficiency (VE; voided volume/(voided volume + residual volume)) and impacts other urodynamic parameters in healthy female volunteers during urodynamic studies.

METHODS

This was a randomized double-blind placebo-controlled study of asymptomatic women aged 18 to 60 years. Subjects completed a visual analog scale and baseline questionnaires to assess pain and lower urinary tract symptoms, respectively. They performed an uninstrumented baseline uroflow, followed by physiologic filling to 250 mL or greater. Subjects were randomized to receive 5 mL of intraurethral aqueous gel or 2% lidocaine gel and then underwent a second uninstrumented uroflow. They then completed complex cystometry, urethral pressure profilometry, and pressure-flow studies.

RESULTS

Twenty-three randomized subjects (12 placebo, 11 lidocaine) were included. Baseline uroflow VE was similar between the placebo and lidocaine groups. After study drug administration, VE was not different between groups (89.3 [85.9-93.9] vs 89.5 [82.5-91.7], P = 0.74). There were also no differences between groups in visual analog scale scores, sensation during cystometry, maximum urethral closure pressure, or micturition parameters (maximum detrusor pressure and detrusor pressure at maximum flow). The placebo group had a lower percentage of interrupted flow pattern (0% vs 36%, P = 0.02) and a lower rate of increased electromyographic activity during micturition (25% vs 73%, P = 0.02).

CONCLUSIONS

In this pilot study of 23 asymptomatic women, intraurethral administration of lidocaine did not decrease VE compared with placebo. The lidocaine group had a greater percentage of interrupted flow patterns and increased electromyographic activity during micturition.

Randomized Controlled Trial to Assess the Impact of High Concentration Intraurethral Lidocaine on Urodynamic Voiding Parameters

OBJECTIVE

To assess whether intraurethral anesthesia decreased voiding efficiency (VE), reduced catheterization pain, and impacted urodynamic parameters in healthy adult females.

METHODS

In a randomized, double-blind, placebo-controlled trial, participants received two 5 mL doses of either intraurethral aqueous gel or 4% lidocaine gel. The primary outcome was VE during randomized condition uroflow, defined as voided volume/(voided volume + residual volume). The secondary outcomes were pain during catheterization and to confirm previously reported pressure-flow changes. A sample size of 10 per group was planned to detect a clinically significant decrease in VE with a power (1-β) of 0.99.

RESULTS

From October to December 2018, 23 women were screened and 18 were randomized to receive placebo (n = 10) or lidocaine (n = 8). Baseline uroflow VE was similar between the placebo and lidocaine groups (88 ± 6.6% vs 91 ± 5.8%, P = .33). After study drug administration, the changes in VE (post-pre) were similar between placebo and lidocaine groups (-5.4 ± 14% vs 1.7 ± 6.4%, P = .21). Visual analog scores were similar following catheterizations (26.7 ± 12.8 mm vs 36.9 ± 26.8 mm, P = .34). The lidocaine group exhibited lower average flow rates per voided volume (0.04 ± 0.02 s^-1 vs 0.02 ± 0.01 s^-1, P = .04).

CONCLUSION

Intraurethral administration of 4% lidocaine did not decrease VE compared to placebo and did not change pain scores following catheterization. In the lidocaine group, the average flow rate per voided volume was lower. The decrease in flow rate after local anesthesia to the urethra may indicate that urethral sensory feedback contributes to voiding in human micturition.

Detrusor Underactivity and the Underactive Bladder: A Systematic Review of Preclinical and Clinical Studies

CONTEXT

Detrusor underactivity (DUA) is a common but relatively under-researched bladder dysfunction. Underactive bladder (UAB) is the symptom-based correlate of DUA. Recently, there has been renewed interest in this topic.

OBJECTIVE

To systematically review and summarise the most recent literature and discuss this in the context of what is already known.

EVIDENCE ACQUISITION

A systematic review of the literature was performed in December 2017 using Medline and Scopus databases. Separate searches of each database used a complex search strategy including "free text" protocols. Search terms included "underactive bladder", "detrusor underactivity", "acontractile bladder", "detrusor failure", "detrusor areflexia", "atonic bladder", "chronic retention", and "impaired bladder contractility".

EVIDENCE SYNTHESIS

The initial search retrieved a total of 1690 studies; of these 44 were included in the final analyses.

CONCLUSIONS

Although there has been an expansion in the literature concerning all aspects of DUA and UAB, knowledge on its epidemiology and aetiopathogenesis is still lacking; there remains a need to develop accurate reproducible diagnostic criteria and effective treatments, in particular drug therapies.

PATIENT SUMMARY

Recently, there has been renewed interest in underactive bladder with expanding research in this area. The lack of simple, reproducible, noninvasive diagnostic criteria has precluded an accurate estimation of the magnitude of the problem. Recent studies have highlighted the potential role of impaired bladder blood supply in causing bladder underactivity.

Vector Flow Visualization of Urinary Flow Dynamics in a Bladder Outlet Obstruction Model

Voiding dysfunction that results from bladder outlet (BO) obstruction is known to alter significantly the dynamics of urine passage through the urinary tract. To non-invasively image this phenomenon on a time-resolved basis, we pursued the first application of a recently developed flow visualization technique called vector projectile imaging (VPI) that can track the spatiotemporal dynamics of flow vector fields at a frame rate of 10,000 fps (based on plane wave excitation and least-squares Doppler vector estimation principles). For this investigation, we designed a new anthropomorphic urethral tract phantom to reconstruct urinary flow dynamics under controlled conditions (300 mm H₂O inlet pressure and atmospheric outlet pressure). Both a normal model and a diseased model with BO obstruction were developed for experimentation. VPI cine loops were derived from these urinary flow phantoms. Results show that VPI is capable of depicting differences in the flow dynamics of normal and diseased urinary tracts. In the case with BO obstruction, VPI depicted the presence of BO flow jet and vortices in the prostatic urethra. The corresponding spatial-maximum flow velocity magnitude was estimated to be 2.43 m/s, and it is significantly faster than that for the normal model (1.52 m/s) and is in line with values derived from computational fluid dynamics simulations. Overall, this investigation demonstrates the feasibility of using vector flow visualization techniques to non-invasively examine internal flow characteristics related to voiding dysfunction in the urethral tract.

Multiple Reflex Pathways Contribute to Bladder Activation by Intraurethral Stimulation in Persons With Spinal Cord Injury

OBJECTIVE

To measure the urodynamic effects of electrical co-stimulation of 2 individual sites in the proximal and distal urethra in persons with spinal cord injury (SCI). This work was motivated by preclinical findings that selective co-stimulation of the cranial urethral sensory nerve and the dorsal genital nerve, which innervate the proximal and distal portions of the urethra, respectively, increased reflex bladder activation and voiding efficiency.

MATERIALS AND METHODS

Electrical co-stimulation of urethral afferents was conducted in persons with chronic SCI during urodynamics. The effects of different frequencies of intraurethral stimulation at multiple urethral locations on bladder pressure and pelvic floor electromyographic activity were measured.

RESULTS

Electromyographic activity indicated that multiple reflex pathways were recruited through stimulation that contributed to bladder activation. The size of reflex bladder contractions evoked by stimulation was dependent on stimulation location or reflex activated and stimulation frequency.

CONCLUSION

Pudendal nerve afferents are a promising target to restore lost bladder control, as stimulation with different frequencies may be used to treat urinary incontinence and increase continent volumes or to generate stimulation-evoked bladder contractions for on-demand voiding. This work identified that co-stimulation of multiple afferent reflex pathways can enhance activation of spinal circuits and may enable improved bladder emptying in SCI when stimulation of a single pathway is not sufficient.

Epidural Spinal Stimulation to Improve Bladder, Bowel, and Sexual Function in Individuals With Spinal Cord Injuries: A Framework for Clinical Research

While some recent studies that apply epidural spinal cord stimulation (SCS) have demonstrated a breakthrough in improvement of the health and quality of the life of persons with spinal cord injury (SCI), the numbers of people who have received SCS are small. This is in sharp contrast to the thousands of persons worldwide living with SCI who have no practical recourse or hope of recovery of lost functions. Thus, the vision is to understand the full potential of this new intervention and to determine if it is safe and effective in a larger cohort, and if it is scalable so that it can be made available to all those who might benefit. To achieve this vision, the National Institute of Biomedical Imaging and Bioengineering called for and organized a consortium of multiple stakeholder groups: foundations addressing paralysis, federal and public agencies, industrial partners, academicians, and researchers, all interested in the same goal. Based on input from consortium participants, we have reasoned that a first step is to define a scalable SCS approach that is effective in restoring lost autonomic physiology, specifically bladder, bowel, and sexual function. These functions are most critical for improving the quality of life of persons living with SCI. This report outlines a framework for conducting the research needed to define such an effective SCS procedure that might seek Food and Drug Administration approval and be implemented at the population level.

Response Properties of Urethral Distension Evoked Unifiber Afferent Potentials in the Lower Urinary Tract

PURPOSE

It is well known that afferent input from the urethra can modulate bladder function. Nevertheless, little is known about the functional properties of urethral afferents. In the current study we investigated the effect of urethral distension on single fiber afferent activities of the lower urinary tract in the female rat.

MATERIALS AND METHODS

Female Sprague Dawley® rats were anesthetized. Single fiber afferent activities were recorded from the left L6 dorsal root and classified by conduction velocity. The response of pelvic and pudendal units on urethral distension (60 seconds) was measured. Two distension diameters were measured in the proximal and the distal urethra.

RESULTS

A total of 93 pelvic and 72 pudendal units were isolated in 15 rats. Of the units 20 (8 pelvic and 12 pudendal) were responsive to urethral distension. Three patterns of response could be distinguished, including a fast adapting and 2 groups of slow adapting afferents. The largest grade of distension resulted in the greatest response in both nerves. Five pelvic and 3 pudendal units responded exclusively to proximal distension, 2 pelvic and 5 pudendal units responded to distal distension, and 1 pelvic and 4 pudendal units responded to both types of distension. The responses were reproducible. No association was found between the type of nerve and the location of the response to distension.

CONCLUSIONS

This electrophysiological study demonstrates the presence of urethral distension evoked afferents in the pelvic and pudendal nerves, and describes their response to distension. Differences in sensory signaling in type and in location were demonstrated. The current technique can be used for further investigation of urethral afferents.

Electrical stimulation for the treatment of lower urinary tract dysfunction after spinal cord injury

Electrical stimulation for bladder control is an alternative to traditional methods of treating neurogenic lower urinary tract dysfunction (NLUTD) resulting from spinal cord injury (SCI). In this review, we systematically discuss the neurophysiology of bladder dysfunction following SCI and the applications of electrical stimulation for bladder control following SCI, spanning from historic clinical approaches to recent pre-clinical studies that offer promising new strategies that may improve the feasibility and success of electrical stimulation therapy in patients with SCI. Electrical stimulation provides a unique opportunity to control bladder function by exploiting neural control mechanisms. Our understanding of the applications and limitations of electrical stimulation for bladder control has improved due to many pre-clinical studies performed in animals and translational clinical studies. Techniques that have emerged as possible opportunities to control bladder function include pudendal nerve stimulation and novel methods of stimulation, such as high frequency nerve block. Further development of novel applications of electrical stimulation will drive progress towards effective therapy for SCI. The optimal solution for restoration of bladder control may encompass a combination of efficient, targeted electrical stimulation, possibly at multiple locations, and pharmacological treatment to enhance symptom control.

Wireless control of intraspinal microstimulation in a rodent model of paralysis

OBJECT

Despite a promising outlook, existing intraspinal microstimulation (ISMS) techniques for restoring functional motor control after spinal cord injury are not yet suitable for use outside a controlled laboratory environment. Thus, successful application of ISMS therapy in humans will require the use of versatile chronic neurostimulation systems. The objective of this study was to establish proof of principle for wireless control of ISMS to evoke controlled motor function in a rodent model of complete spinal cord injury.

METHODS

The lumbar spinal cord in each of 17 fully anesthetized Sprague-Dawley rats was stimulated via ISMS electrodes to evoke hindlimb function. Nine subjects underwent complete surgical transection of the spinal cord at the T-4 level 7 days before stimulation. Targeting for both groups (spinalized and control) was performed under visual inspection via dorsal spinal cord landmarks such as the dorsal root entry zone and the dorsal median fissure. Teflon-insulated stimulating platinum-iridium microwire electrodes (50 μm in diameter, with a 30- to 60-μm exposed tip) were implanted within the ventral gray matter to an approximate depth of 1.8 mm. Electrode implantation was performed using a free-hand delivery technique (n = 12) or a Kopf spinal frame system (n = 5) to compare the efficacy of these 2 commonly used targeting techniques. Stimulation was controlled remotely using a wireless neurostimulation control system. Hindlimb movements evoked by stimulation were tracked via kinematic markers placed on the hips, knees, ankles, and paws. Postmortem fixation and staining of the spinal cord tissue were conducted to determine the final positions of the stimulating electrodes within the spinal cord tissue.

RESULTS

The results show that wireless ISMS was capable of evoking controlled and sustained activation of ankle, knee, and hip muscles in 90% of the spinalized rats (n = 9) and 100% of the healthy control rats (n = 8). No functional differences between movements evoked by either of the 2 targeting techniques were revealed. However, frame-based targeting required fewer electrode penetrations to evoke target movements.

CONCLUSIONS

Clinical restoration of functional movement via ISMS remains a distant goal. However, the technology presented herein represents the first step toward restoring functional independence for individuals with chronic spinal cord injury.

Restoration from acute urinary dysfunction using Utah electrode arrays implanted into the feline pudendal nerve

OBJECTIVES

To investigate intrafascicular pudendal nerve stimulation in felines as a means to restore urinary function in acute models of urinary incontinence, overactive bladder, and underactive bladder.

MATERIALS AND METHODS

Felines were anesthetized, and high-electrode-count (48 electrodes; 25 electrodes/mm(2) ) electrode arrays were implanted intrafascicularly into the pudendal nerve trunk. Electrodes were mapped for their ability to selectively or nonselectively excite the external anal sphincter, external urethral sphincter, and the detrusor bladder muscle. Statistical analysis was carried out to quantify reflexive voiding efficiencies, mean impedances of the microelectrodes used in this study, and to determine what differences, if any, in bladder contraction amplitudes were evoked by different electrode configurations.

RESULTS

Multielectrode arrays implanted into the pudendal nerve trunk were able to selectively and nonselectively excite genitourinary muscles. After inducing urinary incontinence with bilateral pudendal nerve transections (proximal to the implants), electrical stimulation delivered through certain microelectrodes was able to significantly reduce leaking (p = 0.008). Electrical stimulation delivered through detrusor selective electrodes was able to inhibit reflexive bladder contractions and excite bladder contractions, depending on the stimulation frequency. Specific electrode configurations were able to drive significantly (p < 0.001) larger bladder contractions than other electrode configurations, depending on the preparation. Successful reflexively or electrically driven bladder contractions were achieved in 46% and 38% of the preparations, respectively, an observation that has not been noted in previously published feline pudendal stimulation studies.

CONCLUSIONS

Multielectrode arrays implanted intrafascicularly into the pudendal nerve trunk may provide a promising new clinical neuromodulation therapy for the restoration of urinary function.

Urothelial mucosal signaling and the overactive bladder-ICI-RS 2013

There is abundant evidence that the lower urinary tract (LUT) mucosal layer is involved both in mechanosensory functions that regulate bladder contractile activity and in urethral sensation. Changes to the mucosa can be associated with a number of bladder pathologies. For example, alterations of the urothelium and underlying lamina propria at both the molecular and structural levels have been reported in both patients and animals associated with disorders such as bladder pain syndrome and diabetic cystopathy. In contrast to the urinary bladder, much less is known about the urothelium/lamina propria of the bladder neck/proximal urethra. There are important gender differences in the outflow region both anatomically and with respect to innervation, hormonal sensitivity, and location of the external urethral sphincter. There is reasonable evidence to support the view that the mucosal signaling pathway in the proximal urethra is important for normal voiding, but it has also been speculated that the proximal urethra can initiate bladder overactivity. When dysfunctional, the proximal urethra may be an interesting target, for example, botulinum toxin injections aiming at eliminating both urgency and incontinence due to detrusor overactivity.

Development of an ultrasound-guided technique for pudendal nerve block in cat cadavers

The objective of this prospective experimental cadaveric study was to develop an ultrasound-guided technique to perform an anaesthetic pudendal nerve block in male cats. Fifteen fresh cadavers were used for this trial. A detailed anatomical dissection was performed on one cat in order to scrutinise the pudendal nerve and its ramifications. In a second step, the cadavers of six cats were used to test three different ultrasonographic approaches to the pudendal nerve: the deep dorso-lateral, the superficial dorso-lateral and the median transperineal. Although none of the approaches allowed direct ultrasonographical identification of the pudendal nerve branches, the deep dorso-lateral was found to be the most advantageous one in terms of practicability and ability to identify useful and reliable landmarks. Based on these findings, the deep dorso-lateral approach was selected as technique of choice for tracer injections (0.1 ml 1% methylene blue injected bilaterally) in six cat cadavers distinct from those used for the ultrasonographical study. Anatomical dissection revealed a homogeneous spread of the tracer around the pudendal nerve sensory branches in all six cadavers. Finally, computed tomography was performed in two additional cadavers after injection of 0.3 ml/kg (0.15 ml/kg per each injection sites, left and right) contrast medium through the deep dorso-lateral approach in order to obtain a model of volume distribution applicable to local anaesthetics. Our findings in cat cadavers indicate that ultrasound-guided pudendal nerve block is feasible and could be proposed to provide peri-operative analgesia in clinical patients undergoing perineal urethrostomy.

Selective co-stimulation of pudendal afferents enhances bladder activation and improves voiding efficiency

AIMS

Clinical application of pudendal nerve (PN) afferent stimulation to restore bladder emptying in persons with neurological disorders requires increased stimulation-evoked voiding efficiencies (VEs). We tested the hypothesis that selective co-stimulation of multiple PN branches, either bilateral dorsal nerve of the penis (DNP) stimulation or selective stimulation of both the cranial sensory nerve (CSN) and DNP, will evoke larger reflex bladder contractions and result in higher VEs than stimulation of any single afferent pathway alone.

METHODS

We measured the strength of bladder contractions, threshold volumes, and VEs produced by unilateral and bilateral stimulation of the DNP as well as singular and selective unilateral co-stimulation of the DNP and CSN in cats anesthetized with α-chloralose.

RESULTS

Co-stimulation of afferent pathways generated significantly larger isovolumetric bladder contractions and evoked contractions at lower threshold volumes than individual stimulation. Co-stimulation of pudendal afferents also suppressed dyssynergic activity in the external anal sphincter produced by low frequency individual stimulation. VE was significantly improved with co-stimulation (172 ± 6% of distention evoked volumes) over individual stimulation (141 ± 6%).

CONCLUSIONS

Both types of co-stimulation evoked larger bladder contractions and increased VE over individual branch PN afferent stimulation and distention-evoked voiding. The decreased threshold volumes required for reflex bladder activation and increased VEs with co-stimulation support the use of stimulation of multiple individual stimulation-evoked reflexes to improve voiding efficiency.

Selective co-stimulation of pudendal afferents enhances reflex bladder activation

The loss of normal bladder function is common in persons with spinal cord injury (SCI) and negatively impacts their quality of life. Electrical stimulation of pudendal nerve afferents is a promising approach to restore control of bladder function. Pudendal afferent stimulation can generate reflex contraction of the bladder, but the resulting bladder voiding efficiency remains low. The objective of this work was t o evaluate selective co-stimulation of two branches of the pudendal nerve--the cranial urethral sensory nerve (CSN) and the dorsal nerve of the penis (DNP)--as a means to enhance reflex bladder activation and bladder voiding efficiency. In preclinical studies in anesthetized adult cats, co-stimulation of CSN and DNP evoked larger bladder contractions than individual stimulation of either CSN or DNP. In a parallel clinical experiment involving a participant with chronic SCI, co-stimulation of the proximal and distal urethra also produced synergistic augmentation of reflex bladder activity, and thus improved voiding efficiency when compared to reflex distension-evoked voiding. Selective co-stimulation of pudendal afferents is efficacious and should be considered in the development of neural prosthetics for restoration of bladder function in persons with SCI.

Urethral flow-responsive afferents in the cat sacral dorsal root ganglia

Although sensory feedback from the urethra plays an integral role in the regulation of lower urinary tract function, little is known about the properties of flow-responsive primary afferent neurons. The purpose of this study was to characterize the activity of sacral afferents that responded to fluid flow through the urethra. Single neuron action potentials were recorded extracellularly from the S1 and S2 dorsal root ganglia in eight cats anesthetized with α-chloralose. 21 of 116 cells responded to urethral flow but not to mechanical palpation of the perineum, 22 responded to both urethral flow and palpation, and 27 responded to palpation only. 34 of the 43 flow-responsive cells exhibited a firing response to 10 ml flow boluses that could be fit using a power function: FR(t)=a×(t)(b)+c, where FR is firing rate, t is time, and a, b and c are constants. In all 34 cells the 'b' term was negative, indicating that the firing rate slowed over the time course of the urethral flow. In 16 of the 24 cells that were recorded during at least four different flow rates, a power function provided a good fit of the relationship between firing rate and flow rate: FR(flow)=k×(flow)(p)+q, where k, p and q are constants. In each of these 16 cells the 'p' term was positive, indicating that the firing rate tended to increase with increases in flow rate. These are the first data to characterize the properties of flow-responsive afferents in the cat, and reveal properties that parallel those of other afferents.

Functional electrical stimulation for bladder, bowel, and sexual function

The principles of using electrical stimulation of peripheral nerves or nerve roots for restoring useful bladder, bowel, and sexual function after damage or disease of the central nervous system are described. Activation of somatic or parasympathetic efferent nerves can produce contraction of striated or smooth muscle in the bladder, rectum, and sphincters. Activation of afferent nerves can produce reflex activation of somatic muscle and reflex inhibition or activation of smooth muscle in these organs. In clinical practice these techniques have been used to produce effective emptying of the bladder and bowel in patients with spinal cord injury and to improve continence of urine and feces. Stimulation of parasympathetic efferents can produce sustained erection of the penis, and stimulation of the nerves to the seminal vesicles can produce seminal emission. Reflex erection and ejaculation can also be produced by stimulation of afferent nerves. Experimental techniques for controlling emptying and continence by a single device, and prospects for comprehensive control of bladder, bowel, and sexual function by electrical techniques are described. These may include more selective electrodes, inactivation of nerves by specific stimulus parameters, greater use of sensors, and networking of implanted components connected to the central and peripheral nervous system.

Bilateral pudendal afferent stimulation improves bladder emptying in rats with urinary retention

OBJECTIVE

To determine whether bilateral electrical stimulation (BiES) of the transected pudendal sensory nerves could further enhance the voiding efficiency beyond that produced by unilateral electrical stimulation (UniES) of transected pudendal afferents in rats with urinary retention.

MATERIALS AND METHODS

The efficiency of bladder emptying with either UniES or BiES of pudendal nerve afferents was measured after acute bilateral transection of the sensory branch of the pudendal nerve. The effects of UniES and BiES on voiding in a partially denervated bladder and acute spinal transection, respectively, were determined.

RESULTS

The voiding efficiency (VE) was reduced from 69 to 22% after bilateral transection of the sensory branch of the pudendal nerve. UniES or BiES increased the VE to 49-62%. Although in most instances BiES consistently generated more efficient bladder emptying than did UniES, these differences were not significant. Both UniES and BiES increased VE after unilateral pelvic nerve transection, demonstrating efficacy in a partially denervated bladder. The enhancement of VE by either UniES or BiES was preserved after acute T(9)-T(10), demonstrating the spinal origin of this augmenting reflex.

CONCLUSIONS

The results of the present study are consistent with an essential role for pudendal sensory feedback in efficient bladder emptying, and unilateral and bilateral electrical activation of pudendal nerve afferents are equally efficient in improving bladder emptying in an animal model of urinary retention. This could provide an approach to improve bladder emptying in patients with non-obstructive urinary retention.

Electrical stimulation of the urethra evokes bladder contractions and emptying in spinal cord injury men: case studies

OBJECTIVE

Electrical stimulation of the urethra can evoke bladder contractions in persons with spinal cord injury (SCI). The objective of this study was to determine whether electrical stimulation of the urethra could evoke bladder contractions that empty the bladder.

METHODS

The first patient was a 45-year-old man with a T6 ASIA A SCI secondary to a gunshot wound 15 years prior. The second patient was a 51-year-old man with a T2 ASIA A SCI secondary to a fall from scaffolding 2 years prior. Both patients demonstrated neurogenic detrusor overactivity on urodynamics and managed their bladder with clean intermittent catheterization and oxybutynin medication. Following informed consent, each patient discontinued oxybutynin 2 days prior to urodynamic testing. Urodynamics were performed with a custom 12 French balloon catheter mounted with ring-shaped electrodes (3 mm) positioned in the prostatic urethra. After filling the bladder to approximately three-fourth of capacity at a rate of 25 ml/minute, the urethra was stimulated with a range of parameters to determine whether electrical stimulation could evoke a bladder contraction and empty the bladder.

RESULTS

Electrical stimulation of the prostatic urethra evoked bladder contractions (peak detrusor pressures of 60-80 cm H(2)O) that emptied the bladder in both subjects. In the first subject, stimulation (9-12 mA, 20 Hz) emptied 64-75%, leaving post-void residual volumes (PVRs) of 41-20 ml. In the second subject, stimulation (20 mA, 20 Hz) emptied 68-77%, leaving PVRs of 56-45 ml.

CONCLUSION

Urethral stimulation evoked bladder emptying in persons with SCI.

New strategies of pelvic nerves stimulation for recovery of pelvic visceral functions and locomotion in paraplegics

AIMS

To present new strategies of pelvic nerves stimulation to enhance micturition, to control spasticity, and to recover locomotion in paraplegics.

METHODS

Three consecutive patients-Th5, Th7, and Th10 spinal cord injured-underwent laparoscopic transperitoneal implantation of octipolar electrodes to the sciatic and the pudendal nerves and one double extradural Brindley-Finetech electrode bilaterally to the sacral nerve roots S3 and S4. The two octipolar electrodes were connected to an implanted rechargeable generator, while the double Brindley electrode was connected to an implanted Brindley-Finetech receiver block.

RESULTS

Continuous stimulation of the sciatic and pudendal nerves at a frequency of 20 Hz in all three patients permits complete control of the spasticity of the lower extremities and of reflex incontinence. Bladder emptying is obtained by sacral nerve roots stimulation alone in the first patient, by simple interruption of pudendal stimulation in the second ("pudendal-deblockade") and by simultaneous sacral nerve roots stimulation with high-frequency pudendal nerve blockade in the third patient. Functional electrical stimulation of the femoral nerves enables the Th4 paraplegics lower-limb cycling and the two further patients standing and alternative locomotion.

CONCLUSION

This short series indicated that laparoscopic implantation of neuroprothesis to the pelvic nerves offers absolutely new strategies based on new combinations of various reported methods to enhance bladder functions and to recover some locomotion in paraplegics.

Neurophysiology of the lower urinary tract

The lower urinary tract (LUT) has two functions: (1) the storage of waste products in the form of urine and (2) the elimination of those wastes through micturition. The LUT operates in a simple "on-off" fashion, either storing urine or releasing it during voiding. While this activity may seem simple, micturition is controlled by a complex set of peripheral neurons that are, in turn, coordinated by cell groups in the spinal cord, brainstem, and brain. When this careful coordination is interrupted, the control of the bladder is lost, resulting in incontinence or retention of urine. The purpose of this chapter is to review how the neural systems coordinating the activity of the lower urinary tract form neural circuits that are responsible for either maintaining continence (the storage reflex) or inducing micturition (the voiding reflex). We will also discuss the brain centers that enable higher organisms to voluntarily choose the time and place for voiding. Finally, we will discuss how defects in the pathways controlling micturition can lead to urinary incontinence and which treatments may normalize LUT function.

Multiple pudendal sensory pathways reflexly modulate bladder and urethral activity in patients with spinal cord injury

PURPOSE

Electrical stimulation of pudendal afferents can evoke reflex bladder contractions with relaxation of the external urethral sphincter in cats. This voiding reflex is mediated by pudendal sensory fibers innervating the penile and prostatic urethra that engage spinal and spinobulbospinal micturition pathways, respectively. However, clinical translation of this potential therapy in individuals with spinal cord injury is limited by the lack of evidence showing analogous reflex mechanisms in humans. We investigated excitatory pudendal-to-bladder reflexes in 7 individuals with chronic spinal cord injury.

MATERIALS AND METHODS

We recorded isovolumetric bladder pressure and perineal electromyogram in response to intraurethral electrical stimulation at varying amplitudes and frequencies.

RESULTS

Selective electrical stimulation of the proximal (29.7 ± 11.6 cm H(2)O) and distal urethral (23.3 ± 9.28 cm H(2)O) segments evoked sustained reflex bladder contractions in different subsets (3 each) of participants. In contrast, the corresponding reflex perineal electromyogram revealed a differential activation pattern between proximal and distal intraurethral stimulation (normalized electromyogram of 1.3 ± 0.2 and 0.3 ± 0.1, respectively, p <0.05).

CONCLUSIONS

To our knowledge we report the first clinical evidence of 2 independent excitatory pudendal-to-bladder reflex pathways, which in turn differentially modulate efferent pudendal output. Each reflex mechanism involves complex interaction of multiple sensory inputs and may provide a neural substrate to restore micturition after spinal cord injury.

Suppression of reflex urethral responses by sacral dermatome stimulation in an acute spinalized feline model

AIMS

Reflex contractions of the external urethral sphincter (EUS) are a major component of voiding dysfunction after neurological injury or disease. Aberrant urethral reflexes can prevent voiding and cause serious medical complications. Characterizing these urethral reflexes during genitourinary studies is necessary for evaluating novel pharmacological or neuroprosthetic approaches. The objectives of the present study were to generate urethral reflexes in the acute spinal feline, to quantify these reflexes, and to suppress them with electrical stimulation of the sacral dermatomes.

METHODS

This study comprised eight male cats. Anaesthesia was maintained with alpha-chloralose or sodium pentobarbital. The spinal cord was transected between T10 and T12, and nerve cuff electrodes were placed on the extradural S2 sacral roots to provide bladder activation. Bladder and urethral pressures were recorded during and after bladder contractions. Electrical stimulation was applied non-invasively to the sacral dermatomes with commercial surface electrodes.

RESULTS

Urethral reflexes were elicited consistently in six cats. The corresponding urethral pressure spikes were quantified. Putative metrics of urethral reflex activity such as the rate and average magnitude of reflex pressure spikes correlated significantly with standard urodynamic variables. Electrical stimulation of the sacral dermatomes suppressed urethral reflexes in three cats.

CONCLUSIONS

These findings in an acute spinal feline preparation demonstrate a non-invasive means of suppressing undesirable urethral reflexes. Translation of this work to clinical use could improve neuroprostheses for restoring bladder function and enhance treatment of aberrant urethral reflexes in humans.

Aging and the underactive detrusor: a failure of activity or activation?

AIMS

To examine the known and potential contributions of motor, sensory, and biomechanical dysfunctions to the clinical problems of detrusor underactivity and detrusor hyperactivity/impaired contractility.

METHODS

A review of the current literature on non-obstructive voiding dysfunction associated with aging was conducted. The functional impact of age-induced biomechanical tissue change via alterations in sensory transduction is considered.

RESULTS

Impaired contractility has been regarded as etiologic of detrusor underactivity. However, an age-related degradation in detrusor contractility as the primary contributor to impaired bladder emptying has not been conclusively demonstrated. To the extent that detrusor contraction force and duration are dependent upon efferent nerve activity and thus reflex responses to sensory activity, there is a potential impact of impaired sensory function on voiding efficiency. Structural and functional tissue changes accompanying aging may result in altered bladder afferent function, with subsequent reflex impairment of detrusor voiding function.

CONCLUSIONS

The relative contributions of motor, sensory, and biomechanical dysfunctions to impaired voiding performance independent of outlet obstruction associated with aging remain to be elucidated.

Electrical stimulation of the urethra evokes bladder contractions in a woman with spinal cord injury

OBJECTIVE

Electrical stimulation of pudendal urethral afferents generates coordinated micturition in animals and bladder contractions in men after spinal cord injury (SCI), but there is no evidence of an analogous excitatory urethra-spinal-bladder reflex in women. The objective of this study was to determine whether electrical stimulation of the urethra could evoke bladder contractions in a woman with SCI.

CASE REPORT

A 38-year-old woman with a C6 ASIA A SCI who managed her bladder with clean intermittent catheterization and oxybutynin demonstrated neurogenic detrusor overactivity on urodynamics. Oxybutynin was discontinued 2 days prior to urodynamic testing with a custom 12F balloon catheter mounted with ring-shaped electrodes located in the bladder neck, mid urethra, and distal urethra. The inflated balloon was placed against the bladder neck to stabilize the catheter electrodes in place along the urethra. However, the balloon limited emptying during contractions. Urodynamics were performed at a filling rate of 25 mL/minute until a distention-evoked bladder contraction was observed. The urethra was stimulated over a range of bladder volumes and stimulus parameters to determine whether electrical stimulation could evoke a bladder contraction.

FINDINGS

Electrical stimulation via urethral electrodes evoked bladder contractions that were dependent on bladder volume (>70% capacity) and the intensity of stimulation.

CONCLUSIONS

This is the first report of an excitatory urethra-spinal-bladder reflex in a woman with SCI. Future studies will determine whether this reflex can produce bladder emptying.

Finite element modeling and in vivo analysis of electrode configurations for selective stimulation of pudendal afferent fibers

Background

Intraurethral electrical stimulation (IES) of pudendal afferent nerve fibers can evoke both excitatory and inhibitory bladder reflexes in cats. These pudendovesical reflexes are a potential substrate for restoring bladder function in persons with spinal cord injury or other neurological disorders. However, the complex distribution of pudendal afferent fibers along the lower urinary tract presents a challenge when trying to determine the optimal geometry and position of IES electrodes for evoking these reflexes. This study aimed to determine the optimal intraurethral electrode configuration(s) and locations for selectively activating targeted pudendal afferents to aid future preclinical and clinical investigations.

Methods

A finite element model (FEM) of the male cat urethra and surrounding structures was generated to simulate IES with a variety of electrode configurations and locations. The activating functions (AFs) along pudendal afferent branches innervating the cat urethra were determined. Additionally, the thresholds for activation of pudendal afferent branches were measured in α-chloralose anesthetized cats.

Results

Maximum AFs evoked by intraurethral stimulation in the FEM and in vivo threshold intensities were dependent on stimulation location and electrode configuration.

Conclusions

A ring electrode configuration is ideal for IES. Stimulation near the urethral meatus or prostate can activate the pudendal afferent fibers at the lowest intensities, and allowed selective activation of the dorsal penile nerve or cranial sensory nerve, respectively. Electrode location was a more important factor than electrode configuration for determining stimulation threshold intensity and nerve selectivity.

Intraurethral activation of excitatory bladder reflexes in persons with spinal cord injury

Electrical activation of an excitatory reflex between sensory fibers in the pudendal nerve and the bladder has been demonstrated in cats and is a potential means of restoring micturition function in persons with spinal cord injury. We investigated the clinical feasibility of activating this reflex to restore bladder function in persons with spinal cord injury by using intraurethral electrical stimulation to activate pudendal sensory fibers innervating the urethra. Excitatory bladder responses (contractions) were evoked by trains of electrical pulses applied to either the proximal (29.7 +/- 11.6 cmH2O) or distal (30.2 +/- 11.6 cmH2O) segment of the urethra. The results indicate that an excitatory reflex between pudendal nerve afferents and the bladder exists in humans with spinal injury and may provide a substrate for restoring micturition function.

Neural control of the lower urinary tract: peripheral and spinal mechanisms

This review deals with individual components regulating the neural control of the urinary bladder. This article will focus on factors and processes involved in the two modes of operation of the bladder: storage and elimination. Topics included in this review include: (1) The urothelium and its roles in sensor and transducer functions including interactions with other cell types within the bladder wall ("sensory web"), (2) The location and properties of bladder afferents including factors involved in regulating afferent sensitization, (3) The neural control of the pelvic floor muscle and pharmacology of urethral and anal sphincters (focusing on monoamine pathways), (4) Efferent pathways to the urinary bladder, and (5) Abnormalities in bladder function including mechanisms underlying comorbid disorders associated with bladder pain syndrome and incontinence.

Bursting stimulation of proximal urethral afferents improves bladder pressures and voiding

Reflex bladder excitation has been evoked via pudendal nerve, pudendal nerve branch and intraurethral stimulation; however, afferent-evoked bladder emptying has been less efficient than direct activation of the bladder via sacral root stimulation. A stimulation method that improves activation of the urethra-bladder excitatory reflex with minimal sphincter recruitment may lead to improved bladder emptying. Fine wire electrodes were placed in the wall of the urethra in five cats. Placement of electrodes near the proximal urethra evoked bladder contractions with minimal sphincter activation. On these electrodes, lower frequency burst-patterned stimuli evoked greater bladder voiding efficiencies (71.2 +/- 27.8%) than other stimulus patterns on the same electrodes (50.4 +/- 41.5%, p > 0.05) or any stimulus pattern on electrodes that elicited urethral closure (16.5 +/- 12.7%, p < 0.05). Fine wire electrodes specifically targeted afferent fibers in the urethra, indicating the feasibility of clinical evaluations using the same method. This work may improve the translation of next generation neuroprostheses for bladder control.

Intraurethral stimulation for reflex bladder activation depends on stimulation pattern and location

AIMS

Reflex bladder excitation has been demonstrated by stimulation of the pudendal nerve and several of its distal branches. However, excitation parameters have not been consistent and the relationship to anatomical locations within the urethra has not been fully investigated. An improved understanding of the lower urinary tract neurophysiology will improve human studies and neuroprosthetic device development.

METHODS

Intraurethral stimulation was performed in nine cats at near isovolumetric bladder volumes before and/or after spinalization. Bladder excitability profiles were obtained for lower (2 Hz) and higher (33 Hz) frequency stimuli along the urethra between the bladder neck and external meatus.

RESULTS

Higher frequency stimuli were excitable at all urethral locations prior to spinalization but only excitable in the middle and distal urethra after spinalization. Lower frequency stimuli were excitable at proximal and middle locations before spinalization but not excitable at any location after spinalization. In most evaluations, bursting pulse stimulation patterns evoked greater bladder pressures than the dominant continuous frequency (2 or 33 Hz).

CONCLUSIONS

These data indicate the potential presence of two distinct pathways for reflex bladder activation within the urethra: a supra-T10 circuit initiated in the proximal and mid urethra that responds to lower and higher frequency stimuli, and a sacral circuit initiated in the mid and distal urethra that responds to higher frequency stimuli. This work suggests potential anatomical targets and stimulus patterns for clinical evaluations of peripheral nerve-based neuroprostheses for bladder control.

Intraurethral stimulation evokes bladder responses via 2 distinct reflex pathways

PURPOSE

Recent animal studies have shown that selective activation of pudendal nerve branches can evoke bladder responses through 2 distinct reflex pathways. We examined intraurethral electrical stimulation as a minimally invasive means of selectively activating these pathways in the cat.

MATERIALS AND METHODS

Bladder responses evoked by intraurethral electrical stimulation were measured in alpha-chloralose anesthetized male cats at different stimulation frequencies, stimulation intensities and intraurethral locations.

RESULTS

Intraurethral electrical stimulation evoked inhibitory and excitatory bladder reflexes depending on stimulation frequency and location. Stimulation in the penile urethra 0 to 3 cm from the urethral meatus at 33 Hz evoked bladder contraction and at 10 Hz it evoked bladder relaxation. These responses were abolished after bilateral transection of the dorsal penile nerves. Stimulation in the membranous urethra 5 to 7 cm from the urethral meatus at 2, 10 and 33 Hz evoked bladder contractions. These responses were abolished after bilateral transection of the cranial sensory nerves. Following acute spinal cord transection bladder contractions were still evoked by 33 Hz stimulation in the penile urethra but not by stimulation at any frequency in the membranous urethra.

CONCLUSIONS

Intraurethral electrical stimulation selectively evoked bladder responses by activating 2 distinct pudendal afferent pathways. Responses depended on stimulation frequency and location. Intraurethral electrical stimulation is a valid means of determining the pathways involved in bladder responses evoked by pudendal nerve stimulation.

Transcutaneously coupled, high-frequency electrical stimulation of the pudendal nerve blocks external urethral sphincter contractions

BACKGROUND

Detrusor-sphincter dyssynergia is a condition in which reflexive contractions of the external urethral sphincter occur during bladder contractions, preventing the expulsion of urine. High-frequency stimulation (kHz range) has been shown to elicit a fast-acting and reversible block of action potential propagation in peripheral nerves, which may be a useful technique in the management of this condition.

OBJECTIVE

The aim of these experiments was to see if a newly developed stimulus delivery system, capable of transmitting current transcutaneously to remote peripheral nerves using a passive implanted conductor, was an effective way to transmit high-frequency waveforms to the pudendal nerve to block ongoing sphincter contractions.

METHODS

High-frequency waveforms were delivered through the skin to the pudendal nerve using a passive implanted conductor in 6 adult cats anesthetized with isoflurane. Five of the experiments were acute, terminal procedures, and the remaining cat was implanted with a permanent electrode system allowing evaluation for 6 months. Typical stimulation parameters were in the range of 1 to 10 kHz and 1 to 10 mA.

RESULTS

Complete blocking of external urethral sphincter contractions was achieved in 5 of the 6 animals. High-frequency stimulation was also tested in the chronically implanted animal without anesthesia, and the stimulation was tolerated with minimal aversive reactions.

CONCLUSIONS

The transcutaneous passive implanted conductor stimulus delivery system is an effective way to stimulate the pudendal nerve at high frequency, leading to sphincter relaxation. This system may provide a simple means to implement this stimulation paradigm in people with detrusor-sphincter dyssynergia.

Somatic innervation of the feline lower urinary tract

Electrical stimulation of pudendal nerve sensory pathways can evoke excitatory bladder reflexes. However, the precise peripheral innervation pattern of these somatic fibers remains unclear. In adult male cats, we investigated pudendal nerve innervation of the lower urinary tract (LUT) by employing anatomical (Sihler's stain) and electrophysiological (selective electrical nerve stimulation) techniques. The stained specimens revealed differential innervation of the proximal and distal urethrae by fibers derived from the sensory branch of the pudendal nerve. Cranial sensory branch fibers penetrated the prostate to terminate along the intraluminal surface of the urethra, whereas the dorsal nerve of the penis primarily innervated the glans penis. Further examination of the proximal urethra showed a separate pathway (deep perineal nerve) that inserted directly into the external urethral sphincter. These observations were confirmed electrophysiologically by the measured urethral sphincter activity evoked in response to selective nerve stimulation. Electrical activation of the sensory pathway evoked only reflex (latency=8.9+/-1.1 ms) contractions of the urethral muscle, whereas stimulation of the perineal pathway elicited direct (latency=1.3+/-0.1 ms) responses. Our findings identify specific pudendal nerve sensory pathways that can be used potentially to restore bladder function in persons with spinal cord injury and also treat LUT symptoms such as urinary retention.

The feline dorsal nerve of the penis arises from the deep perineal nerve and not the sensory afferent branch

The cat has been used extensively as an animal model for urogenital studies involving the pudendal nerve. However, discrepancies persist in the literature regarding the origin of the dorsal nerve of the penis (DNP). This study used gross dissections and serial histological cross sections to demonstrate that the DNP arises from the deep perineal nerve and not the sensory afferent branch as previously reported. This finding indicates a better than previously appreciated neuroanatomical homology between the cat and human.

Variable patterned pudendal nerve stimuli improves reflex bladder activation

We evaluated variable patterns of pudendal nerve (PN) stimuli for reflex bladder excitation. Reflex activation of the bladder has been demonstrated previously with 20-33 Hz continuous stimulation of PN afferents. Neuronal circuits accessed by afferent mediated pathways may respond better to physiological patterned stimuli than continuous stimulation. Unilateral PN nerve cuffs were placed in neurologically intact male cats. PN stimulation (0.5-100 Hz) was performed under isovolumetric conditions at bladder volumes up to the occurrence of distension evoked reflex contractions. Stimulus evoked reflex bladder contractions were elicited in eight cats. Across all experiments, bursting of 2-10 pulses at 100-200 Hz repeated at continuous stimulation frequencies evoked significantly larger bladder responses than continuous (single pulse) stimulation (52.0+/-44.5%). Bladder excitation was also effective at 1 Hz continuous stimuli, which is lower than typically reported. Variable patterned pulse bursting resulted in greater evoked reflex bladder pressures and increased the potential stimulation parameter space for effective bladder excitation. Improved bladder excitation should increase the efficacy of neuroprostheses for bladder control.

Activation and inhibition of the micturition reflex by penile afferents in the cat

Coordination of the urinary bladder and the external urethral sphincter is controlled by descending projections from the pons and is also subject to modulation by segmental afferents. We quantified the effects on the micturition reflex of sensory inputs from genital afferents traveling in the penile component of the somatic pudendal nerve by electrical stimulation of the dorsal nerve of the penis (DNP) in alpha-chloralose anesthetized male cats. Depending on the frequency of stimulation (range, 1-40 Hz), activation of penile afferents either inhibited contractions of the bladder and promoted urine storage or activated the bladder and produced micturition. Stimulation of the DNP at 5-10 Hz inhibited distension-evoked contractions and increased the maximum bladder capacity before incontinence. Conversely, stimulation at 33 and 40 Hz augmented distension-evoked contractions. When the bladder was filled above a threshold volume (70% of the volume necessary for distension-evoked contractions), stimulation at 20-40 Hz activated de novo the micturition reflex and elicited detrusor contractions that increased voiding efficiency compared with distension-evoked voiding. Electrical stimulation of the DNP with a cuff electrode or percutaneous wire electrode produced similar results. The ability to evoke detrusor contractions by activation of the DNP was preserved following acute spinal cord transection. These results demonstrate a clear role of genital afferents in modulating the micturition reflex and suggest the DNP as a potential target for functional restoration of bladder control using electrical stimulation.

Improved bladder emptying in urinary retention by electrical stimulation of pudendal afferents

Urinary retention is the inability to empty the bladder completely, and may result from bladder hypocontractility, increases in outlet resistance or both. Chronic urinary retention can lead to several urological complications and is often refractory to pharmacologic, behavioral and surgical treatments. We sought to determine whether electrical stimulation of sensory fibers in the pudendal nerve could engage an augmenting reflex and thereby improve bladder emptying in an animal model of urinary retention. We measured the efficiency of bladder emptying with and without concomitant electrical stimulation of pudendal nerve afferents in urethane-anesthetized rats. Voiding efficiency (VE = voided volume/initial volume) was reduced from 72 +/- 7% to 29 +/- 7% following unilateral transection of the sensory branch of the pudendal nerve (UST) and from 70 +/- 5% to 18 +/- 4% following bilateral transection (BST). Unilateral electrical stimulation of the proximal transected sensory pudendal nerve during distention-evoked voiding contractions significantly improved VE. Low-intensity stimulation at frequencies of 1-50 Hz increased VE to 40-51% following UST and to 39-49% following BST, while high-intensity stimulation was ineffective at increasing VE. The increase in VE was mediated by increases in the duration of distention-evoked voiding bladder contractions, rather than increases in contraction amplitude. These results are consistent with an essential role for pudendal sensory feedback in efficient bladder emptying, and raise the possibility that electrical activation of pudendal nerve afferents may provide a new approach to restore efficient bladder emptying in persons with urinary retention.

Bladder activation by selective stimulation of pudendal nerve afferents in the cat

Bladder contractions evoked by pudendal nerve stimulation in both spinal intact and spinal transected cats support the possibility of restoring urinary function in persons with chronic spinal cord injury (SCI). However, electrically evoked bladder responses in persons with SCI were limited to transient contractions at relatively low pressures. This prompted the present study, which presents a detailed quantification of the responses evoked by selective stimulation of individual branches of the pudendal nerve at different stimulation frequencies. In spinal intact cats anesthetized with alpha-chloralose, selective frequency-dependent electrical activation of the sensory (2 Hz<or=f<or=50 Hz), cranial sensory (f<or=5 Hz), dorsal genital (f>or=20 Hz) and rectal perineal (f<or=10 Hz) branches of the pudendal nerve evoked sustained bladder contractions dependent on the stimulation frequency. Contractions evoked by selective electrical stimulation resulted in significant increases in voiding efficiency compared to bladder emptying by distension-evoked contractions (p(ANOVA)<0.05). Acute spinal transection abolished reflex bladder contractions evoked by low frequency stimulation of the cranial sensory or rectal perineal branches, whereas contractions evoked by high frequency stimulation of the dorsal genital branch remained intact. This study presents evidence for two distinct micturition pathways (spino-bulbo-spinal vs. spinal reflexes) activated by selective afferent pudendal nerve stimulation, the latter of which may be applied to restore bladder function in persons with SCI.

Voiding reflex in chronic spinal cord injured cats induced by stimulating and blocking pudendal nerves

AIMS

To induce efficient voiding in chronic spinal cord injured (SCI) cats.

METHODS

Voiding reflexes induced by bladder distension or by electrical stimulation and block of pudendal nerves were investigated in chronic SCI cats under alpha-chloralose anesthesia.

RESULTS

The voiding efficiency in chronic SCI cats induced by bladder distension was very poor compared to that in spinal intact cats (7.3 +/- 0.9% vs. 93.6 +/- 2.0%, P < 0.05). In chronic SCI cats continuous stimulation of the pudendal nerve on one side at 20 Hz induced large amplitude bladder contractions, but failed to induce voiding. However, continuous pudendal nerve stimulation (20 Hz) combined with high-frequency (10 kHz) distal blockade of the ipsilateral pudendal nerve elicited efficient (73.2 +/- 10.7%) voiding. Blocking the pudendal nerves bilaterally produced voiding efficiency (82.5 +/- 4.8%) comparable to the efficiency during voidings induced by bladder distension in spinal intact cats, indicating that the external urethral sphincter (EUS) contraction was caused not only by direct activation of the pudendal efferent fibers, but also by spinal reflex activation of the EUS through the contralateral pudendal nerve. The maximal bladder pressure and average flow rate induced by stimulation and bilateral pudendal nerve block in chronic SCI cats were also comparable to those in spinal intact cats.

CONCLUSIONS

This study shows that after the spinal cord is chronically isolated from the pontine micturition center, bladder distension evokes a transient, inefficient voiding reflex, whereas stimulation of somatic afferent fibers evokes a strong, long duration, spinal bladder reflex that elicits efficient voiding when combined with blockade of somatic efferent fibers in the pudendal nerves.

Pudendal nerve stimulation evokes reflex bladder contractions in persons with chronic spinal cord injury

AIMS

Although electrical stimulation of the pudendal nerve has been shown to evoke reflex micturition-like bladder contractions in both intact and spinalized cats, there is little evidence to suggest that an analogous excitatory reflex exists in humans, particularly those with spinal cord injury (SCI). We present two cases where electrical activation of pudendal nerve afferents was used to evoke excitatory bladder responses.

SUBJECTS AND METHODS

A percutaneously placed catheter electrode was used to electrically stimulate the pudendal nerve trunk in two males with SCI. The response was quantified with recorded changes in detrusor pressure and EMG activity of the external anal sphincter.

RESULTS

In both individuals, frequency specific (f = 20-50 Hz) activation of the pudendal nerve trunk evoked excitatory bladder contractions that also depended on the stimulus amplitude and bladder volume.

CONCLUSION

The results suggest that selective activation of the perineal branches of the pudendal nerve may further augment the excitatory reflex evoked by electrical stimulation.

Role of pudendal afferents in voiding efficiency in the rat

The reciprocal activities of the bladder and external urethral sphincter (EUS) are coordinated by descending projections from the pontine micturition center but are subjected to modulation by peripheral afferent inputs. Transection of the somatic pudendal nerve innervating the striated EUS decreases voiding efficiency and increases residual urine in the rat. The reduction in voiding efficiency was attributed to the lack of phasic bursting activity of the EUS following denervation. However, transection of the pudendal nerve also eliminates somatic sensory feedback that may play a role in voiding. We hypothesized that feedback from pudendal afferents is required for efficient voiding and that the loss of pudendal sensory activity contributes to the observed reduction in voiding efficiency following pudendal nerve transection. Quantitative cystometry in urethane anesthetized female rats following selective transection of pudendal nerve branches, following chemical modulation of urethral afferent activity, and following neuromuscular blockade revealed that pudendal nerve afferents contributed to efficient voiding. Sensory feedback augmented bladder contraction amplitude and duration, thereby increasing the driving force for urine expulsion. Second, sensory feedback was necessary to pattern appropriately the EUS activity into alternating bursts and quiescence during the bladder contraction. These findings demonstrate that the loss of pudendal sensory activity contributes to the reduction in voiding efficiency observed following pudendal nerve transection, and illustrate the importance of urethral sensory feedback in regulating bladder function.

Minimally-invasive electrical stimulation of the pudendal nerve: a pre-clinical study for neural control of the lower urinary tract

AIMS

Electrical stimulation of afferent pudendal nerve fibers can evoke sustained bladder contractions (SBC) in cats, yet evidence of therapeutic efficacy in human subjects is lacking. This pre-clinical study was undertaken to test the hypothesis that robust bladder contractions can be generated with a minimally-invasive needle electrode.

MATERIALS AND METHODS

In seven adult cats, triggered electromyographic (EMG) signals from the external anal sphincter (EAS) were used to minimize the needle-to-nerve distance; while reflex bladder contractions were recorded as 20-sec trains of current pulses of varying amplitude (threshold to 10 mA) and frequency (1-100 Hz) were applied to the nerve. This stimulation paradigm was repeated at successively greater needle-to-nerve distances (0.5 cm intervals) and also at different electrode positions along the nerve.

RESULTS

Electrophysiological access to the pudendal nerve was consistently achieved, as indicated by the average threshold for EAS activation (0.31+/-0.19 mA). Using different combinations of stimulus amplitude and frequency, robust SBCs were evoked in every experiment. More rostral electrode positions exhibited stimulation amplitudes and corresponding maximum bladder pressures (0.68+/-0.36 mA and 25.3+/-3.5 cmH2O, respectively) that were comparable to those of more invasive stimulation methods.

CONCLUSIONS

The needle electrode provides a minimally-invasive approach that will enable the study of reflexes mediated by pudendal afferents in humans, and allow pre-operative testing before implanting a permanent device.

Bladder inhibition or voiding induced by pudendal nerve stimulation in chronic spinal cord injured cats

AIMS

To investigate pudendal-to-bladder spinal reflexes in chronic spinal cord injured (SCI) cats induced by electrical stimulation of the pudendal nerve.

METHODS

Bladder inhibition or voiding induced by pudendal nerve stimulation at different frequencies (3 or 20 Hz) was studied in three female, chronic SCI cats under alpha-chloralose anesthesia.

RESULTS

Voiding induced by a slow infusion (2-4 ml/min) of saline into the bladder was very inefficient (voiding efficiency=7.3%+/-0.9%). Pudendal nerve stimulation at 3 Hz applied during the slow infusion inhibited reflex bladder activity, and significantly increased bladder capacity to 147.2+/-6.1% of its control capacity. When the 3-Hz stimulation was terminated, voiding rapidly occurred and the voiding efficiency was increased to 25.4+/-6.1%, but residual bladder volume was not reduced. Pudendal nerve stimulation at 20 Hz induced large bladder contractions, but failed to induce voiding during the stimulation due to the direct activation of the motor pathway to the external urethral sphincter. However, intermittent pudendal nerve stimulation at 20 Hz induced post-stimulus voiding with 78.3+/-12.1% voiding efficiency. The voiding pressures (39.3+/-6.2 cmH2O) induced by the intermittent pudendal nerve stimulation were higher than the voiding pressures (23.1+/-1.7 cmH2O) induced by bladder distension. The flow rate during post-stimulus voiding induced by the intermittent pudendal nerve stimulation was significantly higher (0.93+/-0.04 ml/sec) than during voiding induced by bladder distension (0.23+/-0.07 ml/sec).

CONCLUSIONS

This study indicates that a neural prosthetic device based on pudendal nerve stimulation might be developed to restore micturition function for people with SCI.

Electrical stimulation of sacral dermatomes in multiple sclerosis patients with neurogenic detrusor overactivity

AIMS

Transcutaneous electrical stimulation of the dorsal penile/clitoral nerve (DPN) has been shown to suppress detrusor contractions in patients with neurogenic detrusor overactivity (NDO). However, the long-term use of surface electrodes in the genital region may not be well tolerated and may introduce hygienic challenges. The aim of this study was to assess whether electrical stimulation of the sacral dermatomes could suppress detrusor contractions in multiple sclerosis (MS) patients with NDO, hereby providing an alternative to DPN stimulation.

MATERIALS AND METHODS

A total of 14 MS patients (8 M, 6 F) with low bladder capacity (<300 ml) and a recent urodynamic study showing detrusor overactivity incontinence participated in the study. Three successive slow fill cystometries (16 ml/min) were carried out in each patient. The first filling served as control filling where no stimulation was applied. In the second and third filling electrical stimulation of either the DPN or sacral dermatomes was applied automatically whenever the detrusor pressure exceeded 10 cmH2O.

RESULTS

The control filling showed detrusor overactivity in 12 of the 14 patients. In 10 of the 12 patients one or more detrusor contractions could be suppressed with DPN stimulation. Electrical stimulation of the sacral dermatomes failed to suppress detrusor contractions in all patients.

CONCLUSIONS

Although therapeutic effects may be present from stimulation of the sacral dermatomes, we were unable to demonstrate any acute effects during urodynamics. For this reason stimulation of the sacral dermatomes is not an option in a system that relies on the acute suppression of a detrusor contraction.

Influence of temperature on urethra to bladder micturition reflex in the awake ewe

AIMS

The flow of fluid along the urethra is known to facilitate detrusor contraction during micturition. This reflex, previously described in awake ewes, helps to achieve complete bladder emptying. In anesthetized cats, another urethra to bladder reflex involving urethral cold receptors has been described. The aim of this study was to investigate whether the urethral reflex first described in awake ewes could also be temperature-dependent.

METHODS

Experiments were performed on 10 healthy ewes. Urethral flows were performed by injecting 10 ml saline (ranging from 17 to 43 degrees C) at the level of the proximal urethra. Catheterization of the bladder was performed so that detrusor pressure was continually recorded during the experiments.

RESULTS

Urethral flows using body temperature saline (37-39 degrees C) consistently evoked detrusor contraction. Urethral flows using saline at temperatures between 40 and 43 degrees C induced detrusor contractions that were not significantly different from those observed at 37-39 degrees C. Urethral flows using saline at temperatures below 37-39 degrees C (17-36 degrees C) resulted in a weaker or absent detrusor contraction.

CONCLUSIONS

In ewes, we have shown that urethral to bladder micturition reflex involving mechanoreceptors is decreased at temperatures below the physiological range. It is suggested that transient receptor potential vanilloid cation channels (e.g., TRPV4 which is activated by sheer/stress flows at near-body temperature) could be involved in this urethra to bladder reflex. In humans, this reflex has hardly been described and is still a matter of debate. Our results reinforce that its full investigation may require systematic use of a range of saline flows at different temperatures.

Effect of tamsulosin on spontaneous bladder contraction in conscious rats with bladder outlet obstruction: Comparison with effect on intraurethral pressure

We investigated the effect of tamsulosin, an alpha(1)-adrenoceptor antagonist, on bladder function, especially spontaneous bladder contractions before micturition (premicturition contraction), in conscious rats with bladder outlet obstruction induced by partial urethral ligation, and compared the results with the effect on intraurethral pressure response in anesthetized rats. In obstructed rats, the alpha(1)-adrenoceptor antagonists tamsulosin, naftopidil and urapidil and non-selective alpha-adrenoceptor antagonist phentolamine inhibited premicturition contractions in a dose-dependent fashion. In contrast, yohimbine, an alpha(2)-adrenoceptor antagonist, and atropine, a muscarinic receptor antagonist, hardly inhibited them. Tamsulosin and urapidil showed clearly inhibitory effects on increases in intraurethral pressure induced by phenylephrine, an alpha(1)-adrenoceptor agonist, in the same dose range as that at which they inhibited premicturition contractions, whereas naftopidil required somewhat higher doses to inhibit increases in intraurethral pressure than those at which it inhibited premicturition contractions. In conclusion, premicturition contractions observed in obstructed rats were sensitive to alpha(1)-adrenoceptor antagonists, but not to alpha(2)-adrenoceptor or muscarinic receptor antagonists. Tamsulosin was shown to be effective against both premicturition contraction and intraurethral pressure response in the same dose range in rats. These results partly support the fact that tamsulosin has improved storage symptoms as well as voiding symptoms in patients with lower urinary tract symptoms associated with bladder outlet obstruction by blocking alpha(1)-adrenoceptors.