Urethral response to nerve stimulation measured by strain gauge force transducer

This paper presents a study of urethral responses to efferent nerve stimulation in dogs. The pelvic, hypogastric and pudendal nerves were stimulated using a programmed instrument under three different in vivo conditions. The preparations consisted of: (A) bladder, urethra, and rectum; (B) urethra and rectum, and (C) urethra only. Stimulation of the pelvic nerve in preparation A resulted in elongation and constriction of the mid and proximal urethra with a resultant rise in pressure. However, this response was reduced in preparations B and C. Similar observations were made with hypogastric nerve stimulation. The results of pudendal nerve stimulation were significantly different, in that the pressure rise occurred in the mild and distal urethra and varied in elongation response.     

Electrophysiological correlates of sensory innervation of the vesico-urethral junction and urethra in man

To investigate urethral sensory innervation in man, cerebral evoked potentials (CEPs) and bulbocavernous reflex (BCR) were recorded by stimulation of vesico-urethral junction (VUJ), prostatic and distal urethra, and penile skin. A specially produced catheter with a pair of electrodes was used for bipolar stimulation along the lower urinary tract. In comparison to the potentials evoked by distal urethral stimulation, the shape differences and protracted latency of CEPs to VUJ stimulation suggest that the distal and proximal urethra are innervated by different peripheral afferents. Similarities of CEPs and BCR latencies produced by prostatic urethral and VUJ stimulation indicate that the sensory innervation of the prostatic urethra is provided by pelvic nerve afferents. The remaining distal parts of the urethra are innervated by pudendal nerves. This is indicated by shape similarities and latency characteristics of both CEPs and BCR when the distal urethra and glans skin are stimulated.     

Urethral response during bladder contraction induced by subcutaneous bethanechol chloride: elicitation of a sympathetic reflex urethral constriction

The responses of the urethra to bladder filling and to subcutaneous bethanechol were studied in a surgically separated bladder-urethra preparation in chloralose anesthetized cats. With the pudendal nerves cut or the neuromuscular junction blocked with gallamine, urethral closure pressure increased during bladder filling and the initial phase of the micturition contraction. It then fell spontaneously or in response to bladder emptying through a vent. With the bladder volume held constant subcutaneous bethanechol induced an increase in basal bladder pressure which culminated in a sustained (reflex) contraction. The urethral constrictor response resembled that seen during the cystometrogram; an increase during the rise in detrusor pressure and a fall during the latter part of the sustained (reflex) contraction. In both cases the urethral response was substantially depressed by hypogastric nerve transection or by intravenous prazosin, implying that the urethral responses were reflexly mediated through the sympathetic system. Intra-arterial bethanechol also produced a urethral constriction, but this response was abolished by atropine and not affected by hypogastric nerve section or prazosin. It is therefore concluded that although bethanechol can produce urethral constriction through a direct muscarinic action on the urethra, it does not do so after subcutaneous administration in a neurally intact cat. The urethral response seen after subcutaneous bethanechol administration is part of the micturition reflex complex and is sympathetically mediated.     

Role of striated and smooth muscle components in the urethral pressure profile in traumatic neurogenic bladders: a neuropharmacological and urodynamic study. Preliminary report

Urodynamic investigations with urethral pressure profile, and vesical, intrarectal and anal pressure recordings were performed in 37 patients with spinal cord lesions. The recordings were done before and after phentolamine injections and/or pudendal nerve blocks to evaluate the respective contribution of sympathetic and somatic innervation to the maximum urethral closure pressure in the mid and distal portions of the membranous urethra. A pressure gradient was demonstrated in the membranous urethra with higher values in the distal than in the mid portion. These results emphasize that the interrupted withdrawal technique is superior to the continuous technique in patients with upper motor neuron bladders. Mid urethral striated and smooth muscle components were shown to represent approximately 60 and 30 per cent of the maximum urethral closure pressure, respectively. In the distal urethra striated and smooth components are more abundant than in the mid portion and contribute in equal proportion to the maximum urethral closure pressure. No substantial role was found for the vascular bed in the maximum urethral closure pressure. The greatest pressure decrease in the mid and distal urethra of patients with lower motor neuron bladders was believed to be an effect of denervation supersensitivity. The results of pudendal blocks showed sphincter dyssynergia to be mediated through pudendal nerves via spinal reflex arcs. Phentolamine effects on bladder activity suggest that blockade of alpha-adrenergic receptors inhibits primarily the transmission in vesical and/or pelvic parasympathetic ganglia and acts secondarily through direct depression of the vesical smooth muscle. Our neuropharmacological results raise strong doubts as to the existence of a sympathetic innervation of the striated urethral muscle in humans.     

A catheter based method to activate urethral sensory nerve fibers

PURPOSE: The ability to control bladder activity would provide a valuable tool to assist individuals with neurological disorders or spinal cord injury (SCI). Recent studies in animal models have shown that bladder contractions can be evoked by electrical stimulation of urethral afferent nerves. We developed and validated in cats a minimally invasive method to stimulate electrically the sensory nerve fibers that innervate the urethra. MATERIALS AND METHODS: The urethra was stimulated electrically along its length via a catheter mounted circumferential electrode in 6 cats. The urethra was similarly stimulated in a male individual with complete SCI. RESULTS: Robust bladder contractions were generated via intraurethral electrical stimulation in all cat experiments. Peak responses were obtained in the proximal and prostatic urethra. In the individual with SCI bladder contractions were generated via intraurethral stimulation at a position 4 cm distal to the bladder. Responses in cats and the human depended on bladder volume. CONCLUSIONS: To our knowledge this study provides the first documentation of generating bladder contractions via intraurethral electrical stimulation in cats and humans. This method provides a research tool for future studies to investigate these pathways in humans. Preliminary human results suggest that urethral afferent mediated neural pathways demonstrated in animal models exist in humans and support the development of neural prostheses using electrical stimulation of these nerves to restore control of bladder function in individuals with neurological disorders or SCI.     

Urethral function after chronic cauda equina lesion in cats. II. The role of autonomically-innervated smooth and striated muscle in distal sphincter dysfunction

We investigated the possibility that distal sphincter dysfunction after chronic sacral rhizotomy in the cat might be due to altered sympathetic influences on smooth and striated muscle. Three months after rhizotomy, sympathetic influences on basal perfusion pressure in the distal sphincteric urethra were significantly decreased. A prazosin-sensitive component of basal perfusion pressure remained after section of all extrinsic urethral innervation in both control and chronic cats. Local intra-arterial 6-hydroxydopamine also abolished this component. After rhizotomy, noradrenaline content in the distal sphincteric urethra was significantly increased but there was no evidence of a change in sensitivity to sympathetic stimulation. A novel prazosin- and atropine-resistant component of the response to hypogastric nerve stimulation was seen in the rhabdosphincteric urethra of chronic cats. This component was abolished by atracurium or hexamethonium. It was significantly greater in cats with S1-3 as compared to S2-3 lesions and was never seen in control cats. It is concluded that autonomic activation of the rhabdosphincter could be a factor in distal sphincter obstruction.     

Urethral function after cystectomy: a canine in vivo experiment

Summary To study the function of the pelvic floor and the isolated urethra after removal of the bladder, 5 male and 5 female mongrel dogs were used in an acute in vivo experiment. Urethral pressure changes secondary to unilateral stimulation of the pelvic and pudendal nerves were recorded. After baseline data of the intact system were documented, the following procedures were carried out: separation of the urethra from the bladder neck (prostate), nerve-sparing cystectomy (cystoprostatectomy), and cold-knife incision through the entire length of the proximal urethra. Pressure recordings were repeated after each step of surgery. Pudendal nerve stimulation resulted in rapid and large pressure rises in the distal urethra (reaction typical of striated muscle). This response remained unchanged after all three surgical steps. Pelvic nerve stimulation provoked pressure rises within the urethra of a pattern typical of smooth muscle. The findings persisted after separation of the urethra from the bladder neck (prostate) and after cystectomy, but were not observed after urethrotomy. Contractions secondary to pudendal nerve stimulation were inhibited by curare, which did not affect the reaction to pelvic nerve stimulation. Our experiments demonstrate that in the dog the continuity of bladder and urethra is not required for the function of urethral closure mechanisms. The contractile potency of the urethral smooth muscles remains intact after nerve-sparing cystectomy. We believe that problems with the baseline continence of surrogate bladders should mainly be ascribed to a lack of surgical caution in preserving the autonomic nerves of cystectomy. A poor response to stress conditions cannot be explained by damage to the neural pathway of the striated sphincter, as the pudendal nerve is not at risk during nerve-sparing cystectomy. In our opinion mechanical malfunction of the striated muscle components secondary to scarring at the site of the anastomosis is the main reason for stress incontinence after orthotopic bladder replacement.     

Seminal emission by electrical stimulation of the spermatic nerve and epididymis

The spermatic nerve and epididymis were stimulated electrically in dogs to elucidate the possibility of artificial seminal emission after bilateral transection of the hypogastric nerves and sympathetic trunks. Before transection, electrical stimulation of a distal end of the severed spermatic nerve caused a trace amount of emission in two dogs and no emission in the remaining four. In contrast, 1 month after the transection, stimulation of a distal end of the severed spermatic nerve caused seminal emission in all six dogs examined, with full seminal volume in four dogs and partial volume in the remaining two. Anatomically, sympathetic nerves originating from the upper portion of the lumbar sympathetic ganglia descended along the spermatic arteries to the testes as spermatic nerves. The present results indicate that spermatic nerves have the potential to generate seminal emission as a compensatory pathway after bilateral transection of the hypogastric nerves. Both direct and percutaneous electrical stimulation of epididymal tails resulted in a full volume of seminal emission in all dogs with transection of both hypogastric nerves and lumbosacral sympathetic trunks as well as in unoperated controls, while high voltage (8 V vs 40-80 V) was required to cause seminal emission by electrical stimulation on the skin surface. Direct stimulation of epididymal tails in men undergoing orchidectomy as treatment for prostatic carcinoma or during biopsy of the contralateral testis in a patient with a testicular tumour, resulted in seminal emission in all five epididymides examined either from the end of the severed vas deferens or in the posterior urethra if the vas deferens was not severed.     

Perineal nerve and transcutaneous spinal stimulation: new methods for investigation of the urethral striated sphincter musculature

The distal motor latencies in the perineal and pudendal nerves were measured in 20 normal subjects using digitally directed pudendal nerve stimulation. The mean pudendal and perineal nerve latencies were 1.9 ms +/- 0.2 (SD) and 2.4 ms +/- 0.2 (SD) respectively. In a further eight normal subjects transcutaneous spinal stimulation was used to record the motor latency from L1 and L4 stimulation sites to the urethral striated sphincter musculature. The mean spinal nerve terminal latencies from L1 and L4 were 4.9 ms +/- 0.3 (SD) and 4.1 ms +/- 0.2 (SD) respectively. These techniques can be applied to the investigation of the nerve supply to the urethral striated musculature in stress urinary incontinence and other disorders affecting the innervation of the anterior pelvic floor musculature.     

Urethral response to sympathetic nerve stimulation in the cat]

The responses of the urethra to hypogastric nerve (HGN) and lumbosacral sympathetic chain (SC) stimulation were observed in 25 chloralose-anesthetized cats. Urethral perfusion pressure was monitored as an index of functional urethral responses. SC was stimulated at four points from L4 to S1. Urethral constrictive response induced by HGN stimulation (delta P:HGN) was significantly larger in male cats than in female cats. But there was no difference between male and female cats in urethral constrictive response induced by SC stimulation (delta P:SC). delta P:HGN was significantly larger than delta P:SC in both sexes, and the ratio of delta P:HGN to delta P:SC (L7-S1) was 2.7 to 1 in male cats and 1.7 to 1 in female cats. delta P:HGN was blocked by the alpha-adrenergic antagonist phentolamine (1-2 mg/kg) and reduced about 50% by autonomic ganglion blockade with hexamethonium bromide (2 mg/min, 25-50 mg). delta P:SC was blocked by both phenotolamine and hexamethonium bromide. In order to examine the pathways of projections of sympathetic fibers from the sacral SC to the urethra, HGN, pelvic nerve and pudendal nerve were transected serially. delta P:SC (L7-S1) was decreased 0%, 12% and 50% by transection of HGN, pelvic nerve and pudendal nerve, respectively. After severance of these three nerves, delta P:SC (L7-S1) was reduced 62%, but not abolished. These data suggest: 1) The effect of HGN to the feline urethra is more prominent than that of SC in both sexes and significantly larger response was noted in male cats with HGN stimulation but not with SC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of selective autonomic and pudendal denervation on the urethral function and development of retention in female dogs

PURPOSE: This trial is an experimental approach to the possible causes of continence and voiding problems after urethra sparing radical cystectomy and orthotopic bladder substitution in women. MATERIALS AND METHODS: Between January 1996 and January 1999 we included 24 mongrel female dogs in this 4-phase study of 6 dogs each. The effects of autonomic denervation of the urethra (phase 1) and urethral transection just distal to the bladder neck (phase 2) on the urethral pressure profile were recorded. In phase 3 the effects of autonomic denervation, urethral transection and pharmacological manipulation of the denervated transected urethra on the urethral pressure profile were studied in succession. In phase 4 the effects of pudendal nerve transection and pharmacological blockade were recorded. In the 12 phases 2 and 3 dogs the transected urethra was re-anastomosed to the bladder neck. Acute experiments were repeated after 2 and 6 months, urethrocystoscopy was done and post-void residual urine was estimated. Two of the latter dogs were sacrificed 6 months after the acute experiment and the urethras were histopathologically examined. RESULTS: Autonomic denervation resulted in a 46% to 48% decrease in mean maximal pressure in the proximal urethra in phases 1 and 3 (p <0.001) with no significant effect on the distal urethra. Urethral transection in phase 2 did not affect the urethral pressure profile. Phentolamine injection after urethral denervation and transection in phase 3 produced a further reduction of 11.3% and 46.3% in mean resting pressure in the proximal and distal urethra, respectively, while succinyl choline produced a 38.1% further decrease in the distal urethra. Unilateral and bilateral pudendal denervation reduced pressure in the distal urethra significantly but not in the proximal urethra. When phentolamine was given thereafter, a further decrease of 38% and 2.4% resulted in resting pressure values in the proximal and distal urethra, respectively. The change in distal urethral pressure was marginally significant after succinyl choline injection (p = 0.05). Results were reproducible after 2 and 6 months. The proximal urethra remained patent with no post-void residual urine after autonomic denervation. There was no significant urethral fibrosis after realignment of the transected urethra in the 2 sacrificed phases 2 and 3 dogs. CONCLUSIONS: From this study we concluded that autonomic denervation reduced pressure in the proximal urethra by less than 50%. Continuity of the urethra with the bladder is not necessary for proper urethral function. After autonomic denervation the proximal urethra remained patent with no subsequent fibrosis. In addition, no post-void residual urine was noted. Bilateral pudendal denervation did not completely block activity of the distal urethra. The nonneuromuscular components had a small role in the creation of urethral closure function.     

Single minimum incision endoscopic radical nephrectomy for renal tumors with preoperative virtual navigation using 3D-CT volume-rendering

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.     

Extradural cold block for selective neurostimulation of the bladder: development of a new technique

PURPOSE: Cryotechnique for selective block of the urethral sphincter and simultaneous activation of the bladder was developed to achieve physiological micturition during sacral anterior root stimulation (SARS). MATERIALS AND METHODS: In ten foxhounds SARS of S2 was carried out while extradurally both spinal nerves S2 were cooled down from positive 25C in a stepwise fashion until a sphincter block was observed. Subsequently, SARS of S2 was performed while the pudendal nerves were cooled down from + 15C. The effects of spinal and pudendal nerve cold block on the urethral sphincter and bladder during SARS and the recovery time were monitored by urodynamic investigation. RESULTS: A complete cold block of the urethral sphincter during spinal nerve cooling was achieved in all cases. During pudendal nerve cooling, the sphincter was completely blocked in two, and incompletely blocked in four dogs. Cold block temperature of the spinal nerves averaged +11.7C and of the pudendal nerves +6.2C. During SARS and spinal nerve cooling, an increase in intravesical pressure up to 13 cm. water was recognized, and recovery time was on average 6.6 minutes. Intravesical pressure remained unchanged during pudendal nerve cooling, with recovery time being less than 1 minute. The cold block was always reversible. CONCLUSIONS: Cryotechnique is an excellent method for selective and reversible block of the urethral sphincter during SARS to avoid detrusor-sphincter-dyssynergia. The application of cryotechnique in functional electrical stimulation leads to an improvement of quality of life in para- or tetraplegic patients because of selective nerve stimulation with optimization of micturition, standing, walking and grasping and does so without the necessity of surgical dorsal root rhizotomy.     

Increased proximal urethral sensory threshold after radical pelvic surgery in women

AIM: To identify factors that potentially influence urethral sensitivity in women. PATIENTS AND METHODS: The current perception threshold was measured by double ring electrodes in the proximal and distal urethra in 120 women. Univariate analysis using Kaplan-Meier models and multivariate analysis applying Cox regressions were performed to identify factors influencing urethral sensitivity in women. RESULTS: In univariate and multivariate analysis, women who had undergone radical pelvic surgery (radical cystectomy n = 12, radical rectal surgery n = 4) showed a significantly (log rank test P < 0.0001) increased proximal urethral sensory threshold compared to those without prior surgery (hazard ratio (HR) 4.17, 95% confidence interval (CI) 2.04-8.51), following vaginal hysterectomy (HR 4.95, 95% CI 2.07-11.85), abdominal hysterectomy (HR 5.96, 95% CI 2.68-13.23), or other non-pelvic surgery (HR 4.86, 95% CI 2.24-10.52). However, distal urethral sensitivity was unaffected by any form of prior surgery. Also other variables assessed, including age, concomitant diseases, urodynamic diagnoses, functional urethral length, and maximum urethral closure pressure at rest had no influence on urethral sensitivity in univariate as well as in multivariate analysis. CONCLUSIONS: Increased proximal but unaffected distal urethral sensory threshold after radical pelvic surgery in women suggests that the afferent nerve fibers from the proximal urethra mainly pass through the pelvic plexus which is prone to damage during radical pelvic surgery, whereas the afferent innervation of the distal urethra is provided by the pudendal nerve. Better understanding the innervation of the proximal and distal urethra may help to improve surgical procedures, especially nerve sparing techniques.     

Anatomic and functional studies of the male and female urethral sphincter

A total of 28 human specimens (14 male, 14 female) was used to perform macro- and microscopic studies on the morphologic basis of the urethral continence mechanism. Furthermore, functional studies were performed in six sheep, with the aim of looking at the pudendal and autonomic innervation of the urethra and the rhabdosphincter, as well as the changes of autonomic innervation after selective denervation. Transurethral ultrasound was performed in 34 continent patients, in order to visualize the contractions of the rhabdosphincter. The membranous urethra is innervated by branches of the autonomic pelvic plexus. The rhabdosphincter is an omega-shaped loop of striated muscle fibers that is innervated by the pudendal nerves. These results are supported by the results of animal experiments that show that the autonomic nerves predominantly innervate and regulate the upper part of the urethra, whereas stimulation of the pudendal nerves leads to a contraction of the lower part of the sheep urethra. In electron-microscopy, marked degeneration of the smooth muscle cells could be seen in the sheep with bilateral denervation.     

Pudendal nerve stimulation of a preparation of isolated guinea-pig urethra

OBJECTIVE: To assess the functional response of the urethral striated muscle to activation of its nerves, using a novel isolated organ-bath preparation. MATERIALS AND METHODS: The urethra of the female guinea-pig was chosen as a suitable model for investigation, as it is functionally and structurally similar to the human urethra. Female Dunkin-Hartley guinea-pigs (400-500 g) were used; for the histochemical and immunohistochemical experiments, unfixed urethras were cryo-sectioned (14 microm thick) and were stained using established methods. For in vitro experiments, whole urethras were suspended vertically, with pudendal nerves intact, for isometric tension and intraluminal pressure recording in a 40-mL organ bath. Drugs were applied directly to the bathing solution. RESULTS: In the striated muscle layer of the urethra there was positive beta-NADPH-diaphorase activity. In organ-bath studies the pudendal nerve-evoked contractions (0.2 ms pulses, 5 s trains, 70 V and 1-100 Hz) were abolished in the presence of tubocurarine (10(-6)m), and unaffected by guanethidine and atropine (both 10(-6)m). Pre-incubation with sodium nitroprusside and SIN-1 chloride significantly reduced the initial peak pressure responses (P < 0.05, anova for paired data) evoked by electrical field stimulation of the pudendal nerves at stimulus parameters of 0.2 ms pulses, 5 s trains, 70 V and 25 Hz. CONCLUSION: Electrically induced contractions were abolished by tubocurarine, confirming that the pudendal nerve innervates the striated muscle of the guinea-pig external urethral sphincter via nicotinic receptors. beta-NADPH-diaphorase histochemistry gave positive staining around guinea-pig striated muscle cells and possibly identified neuromuscular junction sites staining positively for the nitric oxide synthase marker. Together with the results of the organ-bath experiments, the results suggest that the striated muscle cells of the guinea-pig urethra have the machinery to respond to nitric oxide.     

Impact of electrostimulation of neurovascular bundles and pudendal nerves on the membranous urethra in male rabbits

PURPOSE: The pathophysiology of post-prostatectomy incontinence is supposed to be multifactorial. The impact of the neurovascular bundles on sphincter function is still under debate. We clarified the impact of cavernous nerves function on the MU. We compared MU pressure responses in male rabbits following electrophysiological stimulation trials on the neurovascular bundles vs pudendal nerve stimulation. MATERIALS AND METHODS: Six male Chinchilla Bastard rabbits were included in this study. Pudendal and cavernous nerve branches were exposed bilaterally in all animals. Randomized electrostimulation of pudendal nerve fibers and the cavernous nerves, as confirmed by erection,) were done using a biphasic signal form of 0.3 mA for 200 microseconds. Stimulation frequency was changed in a randomized pattern from 10 to 40 Hz. Changes in MU pressure were measured urodynamically via a transurethral microtip catheter placed in the MU. Stimulation responses of the 2 nerve structures were compared. RESULTS: Mean baseline pressure in the MU without stimulation was 23 cm H(2)O (range 20 to 25) in all animals. During unilateral pudendal stimulation the mean pressure response increased highly significantly to 33, 43, 59 and 60 cm H(2)O at 10, 20, 30 and 40 Hz, respectively (p <0.005). In contrast, compared to baseline pressure cavernous nerve stimulation did not result in any significant changes in proximal urethral pressure (mean 23 cm H(2)O, range 20 to 25, p >0.05). CONCLUSIONS: Our results confirm the primacy of the pudendal nerve in the external urethral sphincter innervation. In contrast, stimulation of the cavernous nerves did not produce any pressure changes in the MU. These results confirm that the neurovascular bundles have no functional impact on the MU.     

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.     

Intraoperative nerve stimulation with measurement of urethral sphincter pressure changes during radical retropubic prostatectomy: a feasibility study

PURPOSE: We evaluated the feasibility of using intraoperative nerve stimulation and real-time urodynamic monitoring to identify the intrapelvic innervation of the urethral sphincter during radical retropubic prostatectomy. MATERIALS AND METHODS: Using an intraurethral balloon pressure transducer and nerve stimulator changes in urethral pressure were measured in response to stimulation of the neurovascular bundles, pelvic side wall, bladder neck, rectus muscle and other structures in 8 patients undergoing nerve sparing radical retropubic prostatectomy. Intraurethral pressure changes were charted on an urodynamic monitor and correlated with the anatomical location of stimulation. RESULTS: Stimulation of the neurovascular bundles resulted in measurable and significant (greater than 10 cm. H(2)O) increases in intraurethral pressure in all 8 patients. The mean pressure increase was 22 cm. H(2)O. Neither control structure, that is the bladder neck or rectus, resulted in pressure changes with stimulation. In 60% of the subjects pelvic side wall stimulation resulted in urethral pressure increases, while in 40% this stimulation caused pelvic contraction floor but no pressure increase. The mean pressure changes with side wall stimulation was 14 cm. H(2)O. CONCLUSIONS: Intraoperative stimulation of pelvic neural structures and measurement of changes in urethral pressure in response to stimulation are feasible during radical retropubic prostatectomy. Stimulating the neurovascular bundle consistently results in significant increases in urethral pressure. The finding of an intrapelvic urethral innervation supports the previously published observation that nerve sparing radical retropubic prostatectomy may result in improved continence postoperatively.     

The motor nerve supply of the external urethral sphincter muscles: An electrophysiologic study

The term “intrinsic external urethral sphincter” has recently been applied to the striated muscle immediately surrounding the membranous urethra, thus distinguishing and separating it from the periurethral striated muscle which is a component of the pelvic floor. The innervation of the intrinsic external urethral sphincter is still controversial. Six male patients with a sustained spinal cord lesion above D-4 underwent electrophysiological evaluation of the reflex and direct evoked responses to stimulation of the pudendal nerve branches in the perineal region. Recording of the motor unit potentials was performed using a catheter-mounted concentric needle introduced into the intrinsic external urethral sphincter transurethrally. The results of this study indicate that the pudendal nerve, i.e., somatic, plays an important role in the innervation of the intrinsic external urethral muscle. It does not, however, exclude the possibility that the autonomic nervous system also innervates this muscle.