The effect of external urethral sphincter contraction on the cavernosus muscles and its role in the sexual act

Objectives/Aim A study of the effect of external urethral sphincter contraction on ischio-/bulbo-cavernosus muscles could not be traced in the literature. We investigated the hypothesis that external urethral sphincter contraction induces cavernosus muscles’ contraction. Methods Twenty-one healthy volunteers (age 37.6 ± 9.7 SD years, 12 men, nine women) were studied. The electromyographic response of the ischio- and bulbo-cavernosus muscles to external urethral sphincter stimulation was recorded before and after anesthetization of the external urethral sphincter, and the ischio- and bulbo-cavernosus muscles; the response was also recorded using normal saline instead of lidocaine. Results Upon external urethral sphincter stimulation (five square pulses, 1 ms duration, 53.8 ± 10.2 mA threshold), both cavernosus muscles exhibited increased electromyographic activity with a mean amplitude of 386.2 ± 44.9 μV for the ischio-cavernosus and 318.4 ± 36.6 μV for the bulbo-cavernosus muscle. The mean latency read 16.8 ± 1.3 ms for the ischio-cavernosus muscle and 15.7 ± 1.2 ms for the bulbo-cavernosus muscle. Neither the ischio- nor the bulbo-cavernosus muscle responded to stimulation of the anesthetized external urethral sphincter, but both responded after saline administration. Likewise, the anesthetized ischio- and bulbo-cavernosus muscles showed no response to external urethral sphincter stimulation but responded after saline had been injected. Conclusions Increased electromyographic activity of the two cavernosus muscles on external urethral sphincter stimulation presumably denotes contraction of these two muscles and that this action is probably reflex, mediated through the ‘sphinctero-cavernosus-reflex’. Cavernosus muscles’ contraction assists in the erectile and ejaculatory mechanisms. It is suggested that this reflex be included as an investigative tool in the diagnosis of erectile and ejaculatory disorders, provided further studies are performed.     

Refractoriness of urethral striated sphincter during voiding: studies with afferent pudendal reflex arc stimulation in male subjects

To assess the excitability of the striated sphincter under normal and abnormal conditions, electrostimulation of the periurethral striated sphincter via the dorsal nerve of the penis was done with the patient at rest and during voiding. Monitoring of simultaneous intravesical and intramembranous urethral pressures, and electromyographic responses of the striated sphincter was performed under fluoroscopic guidance in 14 male subjects. The urethral striated sphincter attained a state of relative refractoriness during detrusor contraction (voiding phase) and greater amounts of afferent stimulation were required to elicit sphincter contractile activity compared to the amounts required during resting states. Under conditions of a hyperactive detrusor with synergic voiding, the amounts of stimulation required to elicit striated sphincter responses were higher than those required in normal subjects. On the other hand, under conditions of striated sphincter dyssynergia, minute amounts of afferent stimulation were enough to produce sphincter contraction during voiding.     

Maximum urethral closure pressure and sphincter volume in women with urinary retention

PURPOSE: In 1988 a syndrome of isolated urinary retention in young women that is associated with electromyographic abnormality of the striated urethral sphincter was described. It was hypothesised that urinary retention resulted from a failure of sphincter relaxation. The electromyographic abnormality causes overactivity of the muscle and may induce changes of work hypertrophy. If the hypothesis that the electromyographic abnormality is the cause of urinary retention is correct, we would expect the urethral sphincter to be enlarged and the urethral pressure profile to be increased in these women. We evaluated the role of static urethral pressure profilometry and transvaginal ultrasound in women in urinary retention. MATERIALS AND METHODS: A total of 66 women in complete or partial urinary retention underwent electromyography of the striated urethral sphincter using a concentric needle electrode, followed by urethral pressure profile and/or urethral sphincter volume measurement by transvaginal ultrasound. RESULTS: Maximum urethral closure pressure plus or minus standard deviation was significantly increased in patients with versus without the electromyographic abnormality (103 +/- 26.4 versus 76.7 +/- 18.4 cm. water, p <0.001). Maximum urethral sphincter volume was also increased in women with versus without the abnormality (2.29 +/- 0.64 versus 1.62 +/- 0.32 cm.3, p <0.001). CONCLUSIONS: The results of this study are consistent with the hypothesis that a local sphincter abnormality is the cause of urinary retention in a subgroup of women. Urethral pressure profilometry and sphincter volume measurement are useful for assessing these cases, especially when sphincter electromyography is not readily available.     

Further characterization of the external urethral sphincter in spinal cord injury: study during spinal shock and evolution of responsiveness to alpha-adrenergic stimulation

To shed further insight into its ever evolving concepts, we studied the activity of the external urethral sphincter in patients with spinal cord injury. Study during the phase of acute spinal shock revealed persistent electromyographic activity in the external urethral sphincter and no activity in the external anal sphincter, suggesting the presence of functional dissociation between the 2 sphincters from the onset of acute spinal injury. The genesis of dissociated activity was discussed by reference to recent experiments on the individual differences in motor neuron and muscle subtypes. Only the external urethral sphincter of chronic paraplegics demonstrated a uniformly increased electromyographic activity after alpha-adrenergic stimulation, while the response in the external anal sphincter was variable. The mechanism of increased response to alpha-adrenergic stimulation in the denervated external urethral sphincter appears to reside either in direct postsynaptic stimulation or recruitment of motor neurons other than the somatic pudendal system, since pre-treatment with competitive muscle relaxant failed to block this increased response in the external urethral sphincter.     

Disposable vaginal surface electrode for urethral sphincter electromyography

During the last 2 years we have developed a disposable vaginal surface electrode for electromyographic (EMG) recording from the urethral striated sphincter. We describe the design of the electrode and report the results of laboratory testing, including directional selectivity of the electrode, electrode impedance, testing for movement artefacts and stability of position. Clinical studies which included 138 cystometries with sphincter EMG, 133 pressure-flow EMG studies and four urethral pressure profile studies with sphincter EMG, demonstrated that the electrode gave technically good and reliable electromyographic data. The registration caused no discomfort to the patient and did not disturb the act of micturition. We recommend this technique for the evaluation of urethral striated muscle activity during urodynamic studies in women, since it is simple, inexpensive and reliable.     

Carbon dioxide urethral pressure profilometry before and after external sphincterotomy in spinal cord injury patients

Seven spinal cord injury patients were studied before and after transurethral external sphincterotomy with combined electromyographic and gas urethral pressure profilometry. The technique was simple, rapid, accurate and reproducible in evaluating the completeness of external sphicterotomy. A significant reduction in maximum urethral closure pressure, as well as in the residual urine volume, was a consistent after spincterotomy. The electromyographic profile showed evidence of periurethral striated muscle activity preoperatively in 2 patients with lower motor neuron lesions in whom the bulbocavernosus reflex could not be elicited. Thus, absence of the bulbocavernosus reflex did not eliminate sphincter reflex activity.     

Botulinum toxin in the treatment of chronic urinary retention in women.

Six women were identified as having difficulty in voiding or complete urinary retention due to abnormal myotonic-like electromyographic (EMG) activity in the striated muscle of the urethral sphincter. An attempt was made to improve voiding by injection of botulinum toxin into the striated sphincter muscle. Although 3 patients then developed transient stress incontinence, demonstrating that sufficient botulinum toxin had been given to cause sphincter weakness, no patient had significant symptomatic benefit.     

Urethral sphincter electromyography with vaginal surface electrodes: a comparison with sphincter electromyography recorded via periurethral coaxial, anal sphincter needle and perianal surface electrodes

Urethral sphincter electromyography recording via vaginal surface electrodes was compared to simultaneous sphincter electromyographic registrations obtained with a periurethral coaxial needle electrode and perianal surface or needle electrodes in 10 neurologically intact women. Qualitative similarity of the vaginal surface and periurethral needle electrode recordings was found. Based on this and our previous studies, we conclude that electromyographic recording with vaginal surface electrodes offers a simple and reliable technique to evaluate the striated urethral sphincter during routine urodynamic studies in women.     

Abnormal electromyographic activity (decelerating burst and complex repetitive discharges) in the striated muscle of the urethral sphincter in 5 women with persisting urinary retention

In five women with urinary retention, recordings from the striated muscle of the urethral sphincter revealed highly abnormal electromyographic (EMG) activity. Using a concentric needle electrode, recordings revealed very striking bursts of activity, referred to here as decelerating burst (DB) and complex repetitive discharges (CRD). Such EMG activity is exceedingly unusual in skeletal striated muscle and resembles most closely the rarely encountered condition of "pseudomyotonia". We suggest that this abnormal activity is associated with a failure of relaxation of the striated muscle of the urethral sphincter, which results in chronic retention.     

Functional conditions of micturition induced by selective sacral anterior root stimulation: experimental results in a canine animal model

Electrical stimulation of the sacral anterior roots using conventional rectangular current pulses results in a simultaneous contraction of the urinary bladder and the striated urethral sphincter. Using a tripolar nerve cuff electrode with quasitrapezoidal current pulses and appropriate stimulation parameters, hyperpolarization of the nerve-fiber cell membrane under the anode of the stimulating electrode can reversibly arrest action potential propagation in large myelinated nerve fibers, innervating the striated urethral sphincter, while leaving action potential propagation unaffected in small non-myelinated nerve fibers innervating the urinary bladder smooth muscle (anodal arrest). Using this technique in 19 female mongrel dogs, we studied the effect of bladder filling, level of anesthesia, and sacral deafferentation on bladder pressure, urethral pressure, and urinary flow. Effective micturition could be induced only after complete dorsal rhizotomy, abolishing reflex contraction of the striated urethral sphincter, when blocking quasitrapezoidal current pulses were used for stimulation. Stimulation with rectangular current pulses directly induced a rise in distal urethral pressure, preventing micturition during stimulation.     

Magnetic stimulation of the sacral roots

Magnetic stimulation using an external surface coil induces an electrodynamic field that penetrates various tissues and stimulates peripheral nerves in a similar fashion to conventional electrical stimulation. An 83 mm magnetic surface coil was used to stimulate 11 spinal cord injury (SCI) patients, during which time detrusor activity and evoked potentials of the striated urinary sphincter motor pathways were evaluated. AH patients had urodynamic studies and conventional sacral evoked potentials prior to magnetic stimulation. The mean bladder capacity was 337 ml (range 109–590), mean leak point pressure was 50 cm H₂O (range 10–80), and mean sacral reflex (afferent-efferent) latency was 37.9 ms (range 25.1–49.3). Eight patients had detrusor-sphincter dyssynergia. Magnetic stimulation over the sacral spine at different bladder volumes was performed. Detrusor and striated sphincter responses were recorded during stimulation. In all patients the technique was easy and the results were reproducible. The mean sacral motor pathway (efferent) latency was 27.9 ms (range 18.7–39.6). Using maximal stimulation, no detrusor response was recorded at bladder volumes <200 ml. However, a detrusor response was recorded in 7 patients (>10 cm H₂O in 2, <10 cm H₂O in 5) when the bladder volume was >200 ml. No complications were seen. Sacral evoked potential measurements assess the function and integrity of the sacral arc but it does not distinguish between afferent and efferent pathways. Magnetic stimulation is a safe and effective method to assess the integrity and function of the detrusor and striated sphincter motor (efferent) pathways. When combined with sacral evoked potential studies, the sensory (afferent) pathways can be evaluated indirectly. Independent assessment of the motor (efferent) and sensory (afferent) pathways of the sacral arc has significant implications in the understanding of the pathophysiology of the different types of neuropathic voiding dysfunction. The magnitude of the detrusor contraction induced by magnetic stimulation was too small to allow any conclusions. However, it appears that the detrusor threshold for stimulation increases with increased bladder volumes.     

External sphincter dyssynergia: an abnormal continence reflex

Some of the characteristics of detrusor-external sphincter dyssynergia were examined in 14 patients with traumatic upper motor neuron lesions within 44 weeks of injury. The sacral evoked response latencies of the male patients were shortened at any time after injury. A continence reflex could be demonstrated in most patients at any time after injury. Comparing averaged values for the group at 4-week intervals, resting pressure at the external urethral sphincter and post-void residual volumes reached nadirs at 12 weeks while voiding efficiency peaked at this time. Thus, voiding function appears to be optimal 12 weeks after injury. During reflex detrusor activity, increases in external urethral sphincter electromyographic activity and external urethral sphincter pressure were associated clearly with a positive slope of the intravesical pressure trace, whereas decreases in both parameters were associated with a negative slope. Voiding occurred only during a negative slope. Although propantheline induced detrusor areflexia, episodic peaks in external urethral sphincter pressure and electromyographic activity continued to occur. We propose that external sphincter dyssynergia, which is independent of detrusor contraction, is the continence reflex exaggerated owing to the loss of supraspinal influences. We believe that the multiple patterns of dyssynergia described previously by others are variations, largely owing to technique, of the single pattern we have observed. The observation of synergic-like urethral responses in some patients during a negative slope of the intravesical pressure, even with complete suprasacral spinal lesions, implies existence of a pathway for synergic-like voiding in the spinal cord.     

Facilitatory neuromodulative effect of duloxetine on pudendal motor neurons controlling the urethral pressure: a functional urodynamic study in healthy women

OBJECTIVE: The aim of this functional urodynamic experiment in healthy women was to study the effect of duloxetine, which is a combined serotonin and norepinephrine (5-HT/NE) reuptake inhibitor, on urethral resting pressure, excitability of pudendal motor neurons, and urethral sphincter contractility. METHODS: In 11 healthy female subjects three baseline urethral pressure profiles (UPPs) were obtained to study resting pressure. Afterward the individual motor threshold (MT) for external urethral sphincter (EUS) contraction in response to transcranial magnetic stimulation (TMS) was determined to study the excitability of pudendal motor neurons. Another three UPPs were recorded while sacral root magnetic stimulation (SMS) was performed to evoke reproducible urethral contractions to study urethral sphincter contractility. Then the women received 40 mg duloxetine and the protocol was repeated 4 h after drug administration. The resting pressure values, MT values following TMS, and the EUS pressure amplitudes in response to SMS obtained at baseline were statistically compared to the corresponding values at follow-up after duloxetine. RESULTS: Oral administration of duloxetine significantly lowered MT for EUS contraction in response to TMS (p=0.013). In addition, duloxetine significantly increased EUS pressure amplitudes in response to SMS (p=0.0007, 5 of 11 subjects evaluated) but did not change urethral resting pressures. CONCLUSIONS: This is the first functional, urodynamic controlled study to show that the combined 5-HT/NE reuptake inhibitor duloxetine has a significant effect on the excitability of pudendal motor neurons and on urethral sphincter contractility in healthy women in vivo but no significant effect on urethral resting tone. Our data confirm a facilitatory neuromodulative effect of duloxetine on sphincter motor neurons in humans.     

Electromyographic study of the striated urethral sphincter in type 3 stress incontinence: evidence of myogenic-dominant damages

Objectives. To determine the electromyographic features of the striated urethral sphincter in patients with type 3 stress incontinence (SI) due to intrinsic sphincteric deficiency (ISD).Methods. We performed electromyography (EMG) of the striated urethral sphincter muscle and urodynamic studies in a total of 51 women, 41 female patients with type 3 SI and 10 women with normal urinary control (NUC). The results were analyzed in both groups, and the correlation of EMG findings with the patient characteristics and urodynamic parameters was evaluated.Results. Motor unit potentials (MUP) of SI patients showed significantly shorter duration (P = 0.0014), lower amplitude (P = 0.0008), and larger number of phases (P = 0.0022) compared with those in the NUC group. Thirty (73%) of the SI patients showed an obvious low amplitude (less than 350 μV)/short duration (less than 4.5 milliseconds)/polyphasic pattern and early recruitment of interference activity with low amplitude at voluntary contraction of the striated sphincter, both indicating existence of myogenic damages. These patients showing myogenic damages had significantly lower Valsalva leak point pressure (P = 0.002) and more leakage in the pad-weigh test (P = 0.010) compared with the SI patients without myogenic damage findings.Conclusions. These results suggested that myogenic-dominant damages of the striated urethral sphincter may contribute to the etiology of ISD in most patients with type 3 SI.     

The etiology of urinary retention after surgery for genuine stress incontinence

Transient postoperative urinary retention after stress incontinence surgery is common, and there is no widely accepted method of hastening the return to normal voiding. The etiology of this retention is poorly understood. Failure of the relaxation of the striated external urethral sphincter has been proposed as an etiologic agent, but has not been documented. Ten patients about to undergo a Burch colposuspension or sub-urethral sling, who demonstrated normal preoperative voiding, were recruited to a study of postoperative retention. Hook-wire electromyographic (EMG)probes were placed into the external urethral sphincter while the patients were under anesthesia, and a suprapubic catheter was placed. We performed instrumented voiding trials 1 or 2 days after surgery while continuously recording urethral EMG and intravesical pressure. Two patients demonstrated normal voiding. Two patients were able to void but demonstrated no EMG silencing. Six patients were unable to void and demonstrated persistent EMG activity. Four of these demonstrated no detrusor contraction, whereas two demonstrated detrusor contractions. All patients resumed normal voiding by clinical parameters within 14 days of surgery. Our study supports other research that suggests that failure of relaxation of the striated urethral sphincter contributes to postoperative urinary retention.     

Micturition disturbance in Parkinson's disease

Ten men with longstanding idiopathic Parkinson's disease (IPD) were investigated by urodynamic and electromyographic methods. The urodynamic studies were repeated after stopping anti-Parkinsonian medication for several hours. All patients showed a difference between the two studies, but the changes were unpredictable. Three patients who had high residual urine volumes in both studies were thought to have prostatic obstruction. EMG analysis showed no evidence of a lower motor neurone lesion affecting the striated urethral sphincter. It was concluded that micturition difficulty in the patient with IPD is due to detrusor hyperreflexia, influenced by the basal ganglia, which is not associated with impaired striated urethral sphincter activity.     

Studies of the latency of pelvic floor contraction during peripheral nerve evaluation show that the muscle response is reflexly mediated

PURPOSE: Whether neuromodulation using an implanted sacral nerve stimulator acts by its effects on pelvic afferent or efferent nerves remains to be determined. However, it has been observed that eliciting an "anal wink" is helpful in the optimal siting of the foraminal stimulating electrode. This observation has been interpreted as indicating that a direct effect on efferent pelvic innervation is an important functional component of the technique. We studied the latency of this motor response to determine whether it is consistent with neuromodulation working via a direct efferent mechanism. MATERIALS AND METHODS: We studied 9 women with urinary retention undergoing the first stage of a stimulator implant (peripheral nerve evaluation). Stimulation was applied to an electrode placed in the S3 foramen and the latency of the response of the striated anal sphincter, a contraction which gives rise to the "anal wink," was measured using a concentric needle electrode placed in the striated part of the anal sphincter. RESULTS: Mean latency of response was 98 milliseconds (range 52 to 140), which is approximately 10 times longer than would be expected from that resulting from direct motor nerve stimulation. CONCLUSIONS: Our results indicate that anal sphincter contraction observed during peripheral nerve evaluation is the result of an afferent mediated response.     

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.     

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.     

Adrenergic innervation of the striated muscle of the intrinsic external urethral sphincter from patients with lower motor spinal cord lesion

The adrenergic innervation of smooth and striated muscle components of the intrinsic external urethral sphincter from patients with suprasacral lesions and detrusor-sphincter dyssynergia has been described previously, when no adrenergic nerves were found associated with striated muscle fibers. In our study the intrinsic external urethral sphincter from patients with lower motor neuron lesions and detrusor areflexia was studied histochemically using the glyoxylic acid method to visualize catecholamines. Varicose adrenergic nerves were demonstrated in the smooth muscle. Adrenergic nerve fibers also were found along the edge of individual striated muscle fibers as well as around striated muscle bundles. Blood vessels in both regions of the urethral sphincter were innervated by adrenergic nerves. We conclude that in patients with lower motor neuron lesions and detrusor areflexia there is a substantial invasion by adrenergic nerve fibers in relation to smooth and striated muscle in the urethra, although the function of the nerve fibers is not known.