Anal Sphincter Activity Research Articles

Evaluation of Anal Sphincter with High Resolution Anorectal Manometry and 3D Reconstruction in Patients with Anorectal Malformation

Background: Patients with anorectal malformation (ARM) need long-term follow-up, in order to evaluate fecal continence; the main predictors of longer-term success are the type of ARM, associated anomalies and sacral integrity. Three-Dimensional High Resolution Anorectal Manometry (3D-HRAM) gives detailed information on pressure on the anal complex profile. Our objective was to analyze anal sphincter activity in ARM patients with 3D-HRAM establishing the correlation between manometric and clinical data. Methods: Forty ARM patients were submitted to 3D-HRAM: manometric, anatomical and clinical scores were correlated with each other and with the bowel management response (BM). Results: A positive correlation between all scores and types of ARM was found: in high ARM and in patients with spinal anomalies (regardless to ARM type) lower scores were reported and even after BM they did not achieve good continence. Conclusions: 3D-HRAM gives detailed data on the functional activity of the anal sphincter complex. Our study revealed a correlation between manometric parameters and clinical outcomes, confirming spinal malformations and ARM type as the most important prognostic risk factors for a bad outcome. Specific sphincteric defects can also be explored with manometry, allowing for tailored bowel management strategies.

Leuprolide Acetate, a GnRH Agonist, Improves the Neurogenic Bowel in Ovariectomized Rats with Spinal Cord Injury.

Electromyographic studies have shown that external anal sphincter activity is modified in response to distension in animals with spinal cord injury. Gonadotropin-releasing hormone and its agonist leuprolide acetate have neurotrophic properties in animals with spinal cord injury. This study was to determine the effects of leuprolide acetate treatment on electromyographic activity of the external anal sphincter and anorectal manometry in ovariectomized rats with spinal cord injury. Adult ovariectomized rats were divided in three groups: (a) sham of spinal cord injury, (b) spinal cord injury treated with saline solution, and (c) spinal cord injury treated with leuprolide acetate. The spinal cord injury was induced by clamping at level T9. Leuprolide acetate dosage of 10 μg/kg was proctored intramuscular for 5 weeks, commencing the day after the lesion. Electromyography of the external anal sphincter, anorectal manometry, and volume of the cecum were evaluated in all groups. The electromyographic study of the external anal sphincter activity showed a significant improvement in injured rats treated with leuprolide acetate. Manometric analysis and cecum volume data obtained in animals with leuprolide acetate were very similar to those found in the sham group. These results demonstrate that leuprolide acetate treatment improves the neurogenic colon in ovariectomized rats with spinal cord injury.

Multifractal characteristics of external anal sphincter based on sEMG signals

Up to 40% of patients treated for rectal cancer suffer from therapy-related symptoms. Innervation injury is one of the suggested pathomechanisms of those symptoms hence the development of a valid, non-invasive tool for the assessment of neural systems is crucial. The aim of this work is to study the fractal properties of the surface electromyography signals obtained from patients suffering from rectal cancer. The anal sphincter activity was investigated for the group of 15 patients who underwent surgical treatment. Multifractal detrended fluctuation analysis was implemented to analyze the data, obtained at four different stages: one before treatment and three times after the surgery. The results from the standard detrended fluctuation analysis and empirical mode decomposition methods are presented and compared. The statistically significant differences between the stages of treatment were identified for the selected spectral parameters: width and maximum of the spectrum.

Design of sEMG assembly to detect external anal sphincter activity: a proof of concept

Objective: Conditional trans-rectal stimulation of the pudendal nerve could provide a viable solution to treat hyperreflexive bladder in spinal cord injury. A set threshold of the amplitude estimate of the external anal sphincter surface electromyography (sEMG) may be used as the trigger signal. The efficacy of such a device should be tested in a large scale clinical trial. As such, a probe should remain in situ for several hours while patients attend to their daily routine; the recording electrodes should be designed to be large enough to maintain good contact while observing design constraints. The objective of this study was to arrive at a design for intra-anal sEMG recording electrodes for the subsequent clinical trials while deriving the possible recording and processing parameters. Approach: Having in mind existing solutions and based on theoretical and anatomical considerations, a set of four multi-electrode probes were designed and developed. These were tested in a healthy subject and the measured sEMG traces were recorded and appropriately processed. Main results: It was shown that while comparatively large electrodes record sEMG traces that are not sufficiently correlated with the external anal sphincter contractions, smaller electrodes may not maintain a stable electrode tissue contact. It was shown that 3 mm wide and 1 cm long electrodes with 5 mm inter-electrode spacing, in agreement with Nyquist sampling, placed 1 cm from the orifice may intra-anally record a sEMG trace sufficiently correlated with external anal sphincter activity. Significance: The outcome of this study can be used in any biofeedback, treatment or diagnostic application where the activity of the external anal sphincter sEMG should be detected for an extended period of time.

Systemic glyceryl trinitrate reduces anal sphincter tone: is there a therapeutic indication?

Nitric oxide (NO) has diverse roles as a biological messenger. [1] Topically applied nitrate donors cause relaxation of the internal anal sphincter (IAS) and facilitate healing of anal fissures [2,3]. Systemic nitrates are commonly used for the treatment of ischaemic heart disease, yet the effects of systemically administered nitrates on the smooth muscle of the IAS are unknown. Our aim was to test the hypothesis that systemically administered nitrates at a normal dose, cause inhibition of anal sphincter activity. With fully informed consent, anal manometry was performed on nine volunteers. Maximum and mean anal resting pressure (representing the IAS), maximum squeeze pressure (representing the external anal sphincter), heart rate and blood pressure were measured, before and after administration of a normal 400μg dose of sublingual glyceryl trinitrate spray. Data are expressed as mean (± standard error of the mean (SEM)). In four females and five males ranging from 19 to 50years of age, administration of GTN resulted in a significant reduction in systolic blood pressure from 138 ± 5 to 127 ± 4mmHg, P<0.01. Mean resting pressure, over 5min, was significantly reduced from 70 ± 10 to 62 ± 10mmHg P<0.05. The maximum resting pressure was also significantly reduced from 109 ± 12 to 86 ± 10mmHg P=0.04. Maximum squeeze pressure, heart rate and diastolic blood pressure were not significantly reduced. Systemic nitrates significantly inhibit internal anal sphincter function.

Increased anal basal pressure in chronic anal fissures may be caused by overreaction of the anal-external sphincter continence reflex

Chronic anal fissure is a painful disorder caused by linear ulcers in the distal anal mucosa. Even though it counts as one of the most common benign anorectal disorders, its precise etiology and pathophysiology remains unclear. Current thinking is that anal fissures are caused by anal trauma and pain, which leads to internal anal sphincter hypertonia. Increased anal basal pressure leads to diminished anodermal blood flow and local ischemia, which delays healing and leads to chronic anal fissure. The current treatment of choice for chronic anal fissure is either lateral internal sphincterotomy or botulinum toxin injections.In contrast to current thinking, we hypothesize that the external, rather than the internal, anal sphincter is responsible for increased anal basal pressure in patients suffering from chronic anal fissure. We think that damage to the anal mucosa leads to hypersensitivity of the contact receptors of the anal-external sphincter continence reflex, resulting in overreaction of the reflex. Overreaction causes spasm of the external anal sphincter. This in turn leads to increased anal basal pressure, diminished anodermal blood flow, and ischemia. Ischemia, finally, prevents the anal fissure from healing.Our hypothesis is supported by two findings. The first concerned a chronic anal fissure patient with increased anal basal pressure (170mmHg) who had undergone lateral sphincterotomy. Directly after the operation, while the submucosal anesthetic was still active, basal anal pressure decreased to 80mmHg. Seven hours after the operation, when the anesthetic had completely worn off, basal anal pressure increased again to 125mmHg, even though the internal anal sphincter could no longer be responsible for the increase. Second, in contrast to previous studies, recent studies demonstrated that botulinum toxin influences external anal sphincter activity and, because it is a striated muscle relaxant, it seems reasonable to presume that it affects the striated external anal sphincter, rather than the smooth internal anal sphincter.If our hypothesis is proved correct, the treatment option of lateral internal sphincterotomy should be abandoned in patients suffering from chronic anal fissures, since it fails to eliminate the cause of high anal basal pressure. Additionally, lateral internal sphincterotomy may cause damage to the anal-external sphincter continence reflex, resulting in fecal incontinence. Instead, higher doses of botulinum toxin should be administered to those patients suffering from chronic anal fissure who appeared unresponsive to lower doses.

Surface Electromyography Reliably Records Electrophysiologically Evoked Internal Anal Sphincter Activity: A More Minimally Invasive Approach for Monitoring Extrinsic Innervation

Background: Even in the case of minimally invasive pelvic surgery, sparing of the autonomic nerve supply is a prerequisite for maintaining anal sphincter function. Internal anal sphincter (IAS) innervation could be electrophysiologically identified based on processed electromyographic (EMG) recordings with conventional bipolar needle electrodes (NE). This experimental study aimed for the development of a minimally invasive approach via intra-anal surface EMG for recordings of evoked IAS activity. Methods: Six male pigs underwent nerve-sparing low anterior rectal resection. Electric autonomic nerve stimulations were performed under online-processed EMG of the IAS. EMG recordings were simultaneously carried out with conventional bipolar NE as the reference method and newly developed intra-anal surface electrodes (SE) in different designs. Results: In all experiments, the IAS activity could be continuously visualized via EMG recordings based on NE and SE. The median number of bipolar electric stimulations per animal was 27 (range 5-52). The neurostimulations resulted in significant EMG amplitude increases for both recording types [NE: median 3.0 µV (interquartile range, IQR 2.8-3.5) before stimulation vs. 7.1 µV (IQR 3.9-13.8) during stimulation, p < 0.001; SE: median 3.6 µV (IQR 3.1-4.3) before stimulation vs. 6.8 µV (IQR 4.8-10.3) during stimulation, p < 0.001]. Conclusions: Intra-anal SE enabled reliable EMG of electrophysiologically evoked IAS activity similar to the conventional recording via NE. The transfer of the method to access platforms for transanal total mesorectal excision or robotics may offer a practical more minimally invasive approach for monitoring extrinsic innervation.

No electrophysiological evidence for Onuf's nucleus degeneration causing bladder and bowel symptoms in Huntington's disease patients

In several degenerative neurologic diseases degeneration of Onuf's nucleus has been demonstrated using histologic and electromyographic (EMG) methods. Although Huntington's disease (HD) patients also frequently complain of bladder and bowel symptoms, degeneration of Onuf's nucleus has not been systematically studied in this group. From our inventory of patients with genetically confirmed HD, all patients willing and capable of participating in the study, which utilized several standard questionnaires, were included. The patients reporting bladder/bowel symptoms were also asked to participate in anal sphincter EMG and sacral reflex studies. Of 52 patients (23 men) with genetically confirmed HD, 34 reported bladder/bowel symptoms, and 16 (8 men) of them consented to anal sphincter EMG and sacral reflex studies. Complete pattern of urinary and fecal urgency with incontinence reported 6 (38%), and incomplete 3 (19%) patients, accompanied with episodic diarrhea in another 3 (19%) patients. No patient exhibited quantitative anal sphincter EMG or sacral reflex abnormalities. However, in 81% of patients, decreased tonic anal sphincter activity and/or decreased voluntary activation were found on qualitative EMG. Lower sacral sensory thresholds and shorter reflex latencies were also found in HD patients compared to controls. We found no EMG signs of Onuf's nucleus degeneration in HD patients. The observed decreased anal sphincter tonic activity and voluntary activation, lower sacral sensory thresholds and shorter reflex latencies as well as the reported bladder/bowel symptoms, are probably caused by degeneration of other central nervous system structures. Neurourol. Urodynam. 33:524-530, 2014. © 2013 Wiley Periodicals, Inc.

Patterns of impaired internal anal sphincter activity in patients with anal fissure

The patterns of impaired internal anal sphincter activity were studied in patients with anal fissure (AF). Twenty healthy controls and 61 patients with acute AF were studied, using anorectal manometry with electromyography (EMG), and 53 patients with chronic AF using high-resolution manometry and ultrasonography. Mean and maximal resting anal pressure (MRAP), spontaneous rhythmic slow and ultraslow waves (USW) and relaxation induced by rectal distension were measured. Patients with acute AF had higher mean (106.4±28.1mmHg) and maximal resting anal pressure (161.5±43.7mmHg) than those with chronic AF (P<0.05); 95% of patients had slow waves (SW) and 67% ultraslow waves. Patients with chronic AF had higher mean (92.4±22.6mmHg) and maximal resting anal pressure (117.5±32.0mmHg) than controls and 94% of patients had slow waves and 69% ultraslow waves. Patients with ultraslow waves (with either acute or chronic AF) had increased internal sphincter hypertonicity (mean and maximal resting pressure), decreased internal sphincter relaxation and increased after-contraction following rectal distension. Patients with acute AF had higher hypertonicity than those with chronic AF and both had increased spontaneous rhythmic activity (waves). Patients with AF and ultraslow waves had higher internal anal sphincter hypertonicity and reduced internal sphincter relaxation and enhanced after-contraction following rectal distension.

Online signal processing of internal anal sphincter activity during pelvic autonomic nerve stimulation: a new method to improve the reliability of intra-operative neuromonitoring signals

Intra-operative neuromonitoring is increasingly applied in several surgical disciplines and has been introduced to facilitate pelvic autonomic nerve preservation. Nevertheless, it has been considered a questionable tool for the minimization of risk, as the results are variable and might be misleading. The aim of the present experimental study was to develop an intra-operative neuromonitoring system with improved reliability for monitoring pelvic autonomic nerve function. Fifteen pigs underwent low anterior rectal resection with pelvic autonomic nerve preservation. Intra-operative neuromonitoring was performed under autonomic nerve stimulation with observation of electromyographic signals of the internal anal sphincter and bladder manometry. As the internal anal sphincter frequency spectrum during stimulation was found to be mainly in the range of 5-20 Hz, intra-operative neuromonitoring signals were postoperatively processed by implementation of matching band pass filters. In 10 preliminary experiments, signal processing was performed offline in the postoperative analysis. Of 163 stimulations intra-operatively assessed by the surgeon as positive responses, 135 (83%) were confirmed after signal processing. In the following five consecutive experiments intra-operative online signal processing was realized and demonstrated reliable intra-operative neuromonitoring signals of internal anal sphincter activity with significant increase during pelvic autonomic nerve stimulation [0.5 μV (interquartile range = 0.3-0.7) vs 4.8 μV (interquartile range = 2.5-7.5); P < 0.001]. Online signal processing of internal anal sphincter activity aids reliable identification of pelvic autonomic nerves with potential for improvement of intra-operative neuromonitoring in pelvic surgery.

Effect of rectal distension on voluntary external anal sphincter function in healthy subjects

Quantification of the anorectal reflex function is critical for explaining the physiological control of continence. Reflex external anal sphincter activity increases with rectal distension in a dynamic response. We hypothesized that rectal distension would similarly augment voluntary external anal sphincter function, quantified by measuring the anal maximum squeeze pressure. Fifty-seven subjects (32 men, 25 women; median age 62 years), with normal anal canal manometry and endoanal ultrasound results, underwent a rectal barostat study with simultaneous anal manometry. Stepwise isovolumetric 50-ml distensions (n=35) or isobaric 4-mmHg distensions (n=22) above the minimum distending pressure were performed (up to 200 ml or 16 mmHg respectively), whilst anal resting pressure and maximum squeeze pressure were recorded and compared with the baseline pressure. The distension-induced squeeze increment was calculated as the maximum percentage increase in maximum squeeze pressure with progressive rectal distension. This was observed in 53 of the 57 subjects as a mean ± standard deviation (range) increase of 32.8 ± 24.1 (-5.5 to 97.7)%. The mean ± standard deviation (range) distension-induced squeeze increment in male subjects was 36.1 ± 25.7 (-5.5 to 97.7)% and in female subjects was 28.1 ± 20.1 (-3.8 to 70.2)%. There was no significant difference between the sexes (P=0.194). Rectal distension augments external anal sphincter function, confirming the existence of a dynamic rectoanal response. This may represent a quantifiable and important part of the continence mechanism.

Selective Pelvic Autonomic Nerve Stimulation with Simultaneous Intraoperative Monitoring of Internal Anal Sphincter and Bladder Innervation

Background: Pelvic autonomic nerve preservation avoids postoperative functional disturbances. The aim of this feasibility study was to develop a neuromonitoring system with simultaneous intraoperative verification of internal anal sphincter (IAS) activity and intravesical pressure. Methods: 14 pigs underwent low anterior rectal resection. During intermittent bipolar electric stimulation of the inferior hypogastric plexus (IHP) and the pelvic splanchnic nerves (PSN), electromyographic signals of the IAS and manometry of the urinary bladder were observed simultaneously. Results: Stimulation of IHP and PSN as well as simultaneous intraoperative monitoring could be realized with an adapted neuromonitoring device. Neurostimulation resulted in either bladder or IAS activation or concerted activation of both. Intravesical pressure increase as well as amplitude increase of the IAS neuromonitoring signal did not differ significantly between stimulation of IHP and PSN [6.0 cm H₂O (interquartile range [IQR] 3.5–9.0) vs. 6.0 cm H₂O (IQR 3.0–10.0) and 12.1 µV (IQR 3.0–36.7) vs. 40.1 µV (IQR 9.0–64.3)] (p > 0.05). Conclusions: Pelvic autonomic nerve stimulation with simultaneous intraoperative monitoring of IAS and bladder innervation is feasible. The method may enable neuromonitoring with increasing selectivity for pelvic autonomic nerve preservation.

Pathophysiology of Bowel Dysfunction in Patients with Motor Incomplete Spinal Cord Injury: Comparison with Patients with Motor Complete Spinal Cord Injury

Bowel dysfunction is a major problem in patients with spinal cord injury. Previous work has provided partial information, particularly about motor incomplete lesions. The purposes of this study were to evaluate the pathophysiologic features of neurogenic bowel in patients with motor incomplete spinal cord injury and to compare them with those in patients with motor complete lesions. Fifty-four patients (59% men; mean age, 43 years) with chronic spinal cord injury and fecal incontinence and/or constipation were evaluated; 32 had motor incomplete lesions, and 22 had motor complete lesions. Clinical assessment, colonic transit time, and anorectal manometry were performed. Colonic transit time was delayed similarly in patients with motor complete lesions and those with motor incomplete lesions. Anal squeeze pressure was present in most patients with motor incomplete lesions and absent in all patients with motor complete lesions. The cough-anal reflex was less frequent in patients with motor complete lesions with a neurologic level above T7 (P < 0.05). Rectal sensitivity was less severely impaired in those with motor incomplete lesions (P < 0.05). Most patients in both groups did not show anal relaxation during defecatory maneuvers. Rectal contractions and anal sphincter activity during distention of the rectum were detected more often in patients with motor complete lesions (P < 0.05). Many severe pathophysiologic mechanisms are involved in neurogenic bowel, affecting patients with motor incomplete spinal cord injury similarly to those of patients with motor complete lesions with spinal sacral reflexes. The pathophysiologic mechanisms of constipation are obstructed defecation, weak abdominal muscles, impaired rectal sensation, and delayed colonic transit time; the mechanisms of fecal incontinence are impaired external anal sphincter contraction, uninhibited rectal contractions, and impaired rectal sensation. However, specific evaluation is required in individual cases.

Recovery of the internal anal sphincter and continence after restorative proctocolectomy.

The internal anal sphincter (IAS) was assessed prospectively using electromyography and manometry in 66 patients (48 men) undergoing restorative proctocolectomy to determine its role in the gradual return of continence. Twenty-nine patients received a J pouch and 37 a W reservoir. Some 38 pouches (J, ten; W, 28) were hand-sewn (mucosal proctectomy with endoanal anastomosis) and 28 (J, 19; W, nine) stapled (end-to-end pouch-anal anastomosis 1 cm above the dentate line). Twelve patients underwent a one-stage procedure (all J pouches), while the remainder had a covering loop ileostomy. Each patient was reassessed immediately after restorative proctocolectomy and again at 7 days, 1 month, 4 months, 9 months and 18 months after pouch formation. Internal sphincter electromyographic activity was greatly reduced after pouch-anal anastomosis (median preoperative frequency 0.51 Hz versus immediate postoperative frequency 0.21 Hz, P < 0.003) and gradually recovered from 4 months after surgery. At 18 months, measurements of IAS function had not fully recovered to preoperative values (median frequency 0.31 Hz; P < 0.03). Resting anal pressures (median preoperative value 99 cmH2O) decreased by over 50 per cent after surgery (median immediate postoperative resting pressure 44 cmH2O) and recovered gradually but incompletely (median pressure at 18 months 63 cmH2O). Eleven patients reported leakage in the follow-up period. The median (range) resting pressure in these patients (54 (40-71) cmH2O) was not significantly different at 9 months from that of those who were continent either before or after operation (59 (46-68) cmH2O). Prolonged recordings in patients with faecal leakage revealed evidence of high-pressure pouch waves that overwhelmed anal sphincter pressures and coincided with leakage. These episodes were most common during sleep, when anal sphincter activity was reduced.

A Model of Neural Cross-Talk and Irritation in the Pelvis: Implications for the Overlap of Chronic Pelvic Pain Disorders

Irritable bowel syndrome, interstitial cystitis, and other chronic pelvic pain (CPP) disorders often occur concomitantly. Neural cross-talk may play a role in the overlap of CPP disorders via the convergence of pelvic afferents. We investigated the hypothesis that afferent irritation of one pelvic organ may adversely influence and sensitize another via neural interactions. We measured pelvic organ smooth muscle and striated muscle reflexes during micturition and colorectal distention (CRD) in urethane-anesthetized rats. The effects of acute cystitis on distal colonic sensory thresholds to CRD and the effects of acute colonic irritation on micturition parameters were assessed. External urethral sphincter (EUS) electromyography (EMG) was typical for the rat, with phasic firing during micturition. External anal sphincter EMG also showed phasic firing during micturition in synchrony with EUS activity but, in addition, showed both tonic bursts and phasic firing independent of EUS activity. Before bladder irritation, graded CRDs to 40 cm H2O produced no notable changes in abdominal wall EMG activity. Following acute bladder irritation, dramatic increases in abdominal wall EMG activity in response to CRD were observed at much lower distention pressures, indicating colonic afferent sensitization. Analogously, following acute colonic irritation, bladder contraction frequency increased 66%, suggesting sensitization of lower urinary tract afferents. We report compelling evidence of bidirectional cross-sensitization of the colon and lower urinary tract in a novel experimental model. This cross-sensitization may account for the substantial overlap of CPP disorders; however, further studies are needed to fully characterize these pathways.

Utilidad de la manometría anorrectal para el diagnóstico y tratamiento de la encopresis

Biofeedback based on anomanometric techniques has been shown to be effective in the treatment of children with encopresis. The long-term efficacy of biofeedback and which variables of anorectal manometry (anorectal manometry) could help to establish biofeedback indications are currently the subject of debate. To identify which variables of anorectal manometry, in addition to symptoms, could be useful in deciding which patients could benefit from biofeedback therapy and to assess the outcome of this treatment. Anorectal manometry was performed in 88 patients, who were referred to our service complaining of soiling at least once a month for a minimum of 6 months after a period of normal continence of 1 year or more. The chronological and mental age of the patients was 4 years. All patients were otherwise in good health and had shown no response to medical treatment. The following variables were studied: anal canal profile, rectoanal inhibitory reflex (RAIR), continence reflex, rectal sensitivity, external anal sphincter (EAS) activity and defecatory maneuver. The patients were divided into two groups, according to clinical and anomanometric impairment, and the most affected patients (n = 41) underwent biofeedback therapy. The indications and outcome of biofeedback were assessed through clinical course and anorectal manometry. In the statistical analysis, the mean and standard deviation were calculated. The chi-squared test with Yates' correction was used to compare clinical and manometric qualitative parameters; Student's t-test was used to compare quantitative parameters; nonparametric tests consisted of the Mann-Whitney test and the Wilcoxon test was used for paired data. Patients treated with biofeedback therapy presented shorter anal canal, greater pressure in the rectal ampulla (P < 0.001), decreased pressure in the anal canal (P < 0.05), lesser distension of the EAS on provoking RAIR, lower presence of the continence reflex (P < 0.01), lower rectal sensitivity, and a worse response of the striated sphincteric muscle and of the defecatory maneuver (P < 0.001). Seventy-eight percent of the patients had a good response to biofeedback therapy. Pressure in the anal canal and rectal sensitivity improved (P < 0.001) with normality on straining in 11 out of 15 patients. These good results persisted in a long-term follow-up of 10 patients. Eight of 10 patients who did not undergo biofeedback therapy showed persistent encopresis (P < 0.001). Anorectal manometry detected disturbances, chiefly in the activity of the EAS, which are useful in indicating biofeedback therapy in children with secondary encopresis. Biofeedback therapy seems to produce favorable long-term results in the majority of the most severely affected patients.

Central muscarinic inhibition of lower urinary tract nociception

Previous studies indicate cholinergic systems suppress somatic nociception. The present studies determined if cholinergic muscarinic systems suppress visceral nociception, specifically, chemical irritation of the lower urinary tract. Bladders of urethane-anesthetized rats were cannulated through the dome for continuous-infusion cystometrogram recordings. EMG electrodes recorded anal sphincter activity. Infusion of 0.5% acetic acid into the bladder to produce irritation increased bladder activity and anal sphincter activity (i.e. activation of a nociceptive vesicoanal reflex). Oxotremorine (a muscarinic agonist) and (−)butylthio[2.2.2] (a mixed muscarinic agonist/antagonist) dose-dependently inhibited vesicoanal reflex activity. This inhibition was antagonized by atropine (a centrally active muscarinic antagonist) but not by scopolamine methylbromide (a peripherally restricted muscarinic antagonist). Physostigmine (a centrally active cholinesterase inhibitor) also dose-dependently inhibited vesicoanal reflex activity in an atropine-sensitive manner, while neostigmine (a peripherally restricted cholinesterase inhibitor) did not. Atropine alone (i.e. administered without prior administration of muscarinic agonist or cholinesterase inhibitor) produced robust but transient (15 min) increases in vesicoanal activity and bladder activity under conditions of acetic acid infusion into the bladder. Under conditions of saline infusion into the bladder, atropine had the opposite effect on bladder activity (i.e. inhibition). These studies indicate that an endogenous cholinergic muscarinic system can be activated by lower urinary tract irritation to suppress visceral nociception through central nervous system mechanisms.

Alpha-1 adrenoceptor blockade: potential new treatment for anal fissures.

Patients with chronic anal fissures are known to have high resting anal pressures that return to normal after successful surgical treatment. Internal anal sphincter activity is increased by sympathetic excitatory innervation via alpha adrenoceptors. The objective of this study was to determine the effect of alpha-1 adrenoceptor blockade on anal sphincter pressure in patients with and without chronic anal fissures. The effect on the anal canal pressure profile of a single oral 20 mg dose of indoramin, an alpha-1 adrenoceptor antagonist, on seven patients with chronic anal fissure and six healthy patients without a fissure was investigated. Indoramin reduced anal resting pressures in those with anal fissure by a mean of 35.8 percent, from 106.9 +/- 22.15 cm H2O to 68.6 +/- 20.35 cm H2O, and in those without anal fissure by a mean of 39.9 percent, from 84.17 +/- 27.46 cm H2O to 52.17 +/- 24.78 cm H2O, after one hour. This pressure reduction persisted at three hours, and its magnitude is comparable to that obtained after internal sphincterotomy. The pressure reduction occurred over the whole length of the anal canal. It is proposed that alpha-1 adrenoceptor antagonists could be a suitable treatment for chronic anal fissure and other painful conditions where reduction in anal pressure is warranted.

Vesicoanal, urethroanal, and urethrovesical reflexes initiated by lower urinary tract irritation in the rat.

Irritation of the urinary bladder causes activation of normally "silent" nociceptive primary afferent fibers. In the present study, it is reported that irritation of the urinary bladder or urethra with infusion of 0.5% acetic acid robustly activates motoneurons that innervate the striated muscle of the external anal sphincter via spinal reflex mechanisms. The activation of anal motoneurons following irritation of the bladder and urethra are termed vesicoanal and urethroanal reflexes, respectively. The reflexes can be mimicked by acute application of capsaicin to the bladder and urethra, and they show desensitization following prolonged topical application of capsaicin or following chronic systemic pretreatment with capsaicin. The reflexes can be demonstrated in chronic spinal cord-transected animals, indicating that the reflex pathways are organized within the spinal cord. The urethroanal reflex is also physiologically activated by urethral distension and/or increases in intraluminal pressure. In addition to activation of anal sphincter activity, slight distension, pressure increases, or instillation of 0.5% acetic acid into the urethra inhibited bladder contractions through activation of an inhibitory urethrovesical reflex. These reflexes are discussed in terms of clinical characteristics of urethritis and prostatitis. Anecdotally, it was discovered that the bladder can buffer acetic acid.

Standardisation of anal sphincter EMG: high and low threshold motor units

Objective: The anal sphincter muscle has a proportion of low threshold motor units (MUs) that are continuously active and other, recruitable high threshold MUs. In standard EMG recordings, motor unit potentials (MUPs) of the later seem to be of higher amplitudes. A quantitative EMG study was performed to assess possible consequences of sampling MUPs at different levels of sphincter activation.Methods: Fifteen females without uroneurological disorders were studied. After insertion, standard concentric EMG needle was left in the anal sphincter muscle undisturbed for 1 min; then 30 s of the remaining continuous, and 1 min of voluntarily increased EMG activity were recorded on a DAT recorder. MUPs were collected and analysed by ‘Multi-MUP’ analysis. MUPs analysed during relaxation constituted the ‘low threshold MUP pool’. MUPs sampled on activation were checked for those, already sampled during relaxation, (which were discarded), and the remaining MUPs constituted the ‘high threshold MUP pool’. Parameters of both MUP pools were compared.Results: High threshold MUPs were found to be significantly larger than low threshold MUPs.Conclusions: EMG investigator should be aware of the differences of MUPs sampled at various anal sphincter activity levels. For the technique of ‘Multi-MUP’ analysis sampling at an activity level which provides 3–5 MUPs per detection site would seem practical, providing a standardised approach suitable for comparing normative data with individual findings from most patients.