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

Aim 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. Method 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. Results 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). Conclusion 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.     

Effect of anterior resection on anal sphincter function

Minor difficulties with continence may occur after low anterior resection. Intraoperative injury to the internal anal sphincter or its nerve supply may contribute to this. To study the effect of low anterior resection on the anal sphincter mechanism, anal manometry was performed on 20 patients before and 10 days after resection. Fifteen patients were studied again 6 months after operation. Resting, maximum squeeze and squeeze increment pressures were recorded. Intraoperative manometry (n = 11) and presacral nerve stimulation (n = 6) were performed to determine whether peroperative injury to the internal anal sphincter had occurred. Resting and maximum squeeze anal canal pressures were reduced by low anterior resection, and did not recover. The squeeze pressure increment did not change. Division of the inferior mesenteric artery, full mobilization of the rectum and mesorectum, and rectal transection did not affect resting anal pressure, which was reduced after EEA anastomosis (mean (s.e.m.) before, 40(5) mmHg; after, 27(4) mmHg; P less than 0.05, n = 5). Presacral nerve stimulation produced relaxation of the internal sphincter. Anal sphincter pressures are reduced after low anterior resection. The external anal sphincter and the nerve supply to the internal anal sphincter appear intact. A direct injury to the internal sphincter is postulated.     

Results of repeat anal sphincter repair

BACKGROUND: Patients with a poor outcome from anterior sphincter repair may be candidates for dynamic graciloplasty, artificial bowel sphincter implantation or a secondary repair. This study examines the outcome of repeat overlap repairs in these patients. METHODS: Twenty-six of 235 patients undergoing a sphincter repair (median age 43 (range 23-63) years) underwent repeat repair from May 1994 to April 1997. Twenty-three patients were available for follow-up. Clinical evaluation included a satisfaction scale from 1 to 10, the patient's assessment of percentage improvement, ability to defer defaecation before and after operation, and Wexner continence scores before and after operation. Manometric studies were performed in 21 patients before and 17 patients after operation, and anal ultrasonography was undertaken in 17 patients before and 14 patients after operation. External sphincter defects were present on all preoperative scans. RESULTS: At a median follow-up of 20 (range 5-42) months, 15 patients felt that they were 50 per cent or more improved after operation. On the satisfaction scale of 1-10 the median score was 7 (range 1-10). There was a significant improvement in the Wexner continence score from 19 (range 17-20) before operation to 12 (range 1-20) after operation (P < 0.001). Ability to defer defaecation improved significantly from less than 5 min in all patients before operation to greater than 15 min in six patients after operation. Ultrasonography showed good overlap of the external sphincter muscle in eight of 14 patients. All patients who failed to improve showed a residual defect on ultrasonography. CONCLUSION: Repeat anterior repair produces a significant improvement in continence score and ability to defer defaecation in patients with obstetric sphincter damage. Clinical improvement correlates closely with an improvement in the appearance on endoanal ultrasonography.     

Fatigue rate of the external anal sphincter

Aim Studies of skeletal muscle show that fatigue rate corresponds to the proportion of fast‐twitch and slow‐twitch fibres that are present in the muscle. Limited work has been done on the fatigue rate of the external anal sphincter. We have prospectively studied fatigability of the external anal sphincter in women with faecal incontinence and women with normal bowel control. Method Anorectal manometry was measured by a station‐pull technique using a water‐filled microballoon. Fatigue rate was calculated from anal pressure measurements taken every 0.1 s over a 20‐s squeeze. Results Women with faecal incontinence (n = 88, median ?12 cmH₂O/min) were less susceptible to fatigue than women with normal bowel control (n = 36, median ?43 cmH₂O/min) (P < 0.01). The external anal sphincter was less susceptible to fatigue with increasing age (P < 0.01, r = 0.499). In women with normal bowel control and in women with faecal incontinence fatigue rate was negatively correlated with maximum squeeze pressure (P < 0.01, r = ?0.287; P < 0.01, r = ?0.579). Conclusion The external anal sphincter was less susceptible to fatigue with increasing age. Women with faecal incontinence have a weaker but more fatigue‐resistant external anal sphincter. This might correspond to a higher proportion of slow‐twitch muscle fibres. Histological studies are needed to examine this hypothesis.     

A novel animal model of long-term sustainable anal sphincter dysfunction

Background

Although intersphincteric resection can avoid the need for permanent colostomy in patients with lower rectal cancer, it sometimes causes anal sphincter dysfunction, thus resulting in a lifelong, debilitating disorder due to incontinence of solid and liquid stool. The development of regenerative medicine could improve this condition by regenerating impaired anal muscle. In order to prove this hypothesis, preliminary experiments in animals will be indispensable; however, an adequate animal model is currently lacking. The purpose of this study was to establish a novel animal model with long-term sustainable anal sphincter dysfunction.

Materials and methods

Twenty male Sprague-Dawley rats were allocated into sham operation (n = 10) and anal sphincter resection (ASR) (n = 10) groups. The ASR group underwent removal of the left half of both the internal and external anal sphincters. Both groups were evaluated for anal function by measuring their resting pressure before surgery and on postoperative day (POD) 1, 7, 14, and 28.

Results

The rats in the sham operation group recovered their anal pressure up to baseline on POD 7. The rats in the ASR group showed a significant decrease in anal pressure on POD 1 (P < 0.0001) compared with the baseline, and kept this low pressure until POD 28 (P < 0.0001). The defect of the anal sphincter muscle was confirmed histologically in the ASR group on POD 28.

Conclusions

The present novel model exhibits continuous anal sphincter dysfunction for at least 1 mo and may contribute to further studies evaluating the efficacy of therapies such as regenerative medicine.     

Injured external anal sphincter in erectile dysfunction

The purpose of this study was to investigate the function of the bulbocavernosus muscle in patients with faecal incontinence as a result of injury to the external anal sphincter, and to find out whether faecal incontinence had any role in erectile dysfunction. The study comprised 16 men (age 41.6+/-6.8 years) whose erectile dysfunction and faecal incontinence followed an operation for anal fistula. Erection could not be maintained until ejaculation, which, if it did occur, was not in jets. Ten healthy volunteers acted as controls. The activity of the external anal sphincter and the bulbocavernosus muscle was recorded by electromyography; anal and penile bulb pressures were also recorded. Investigations showed that erectile function was normal. The external anal sphincter was repaired, and faecal control and erectile dysfunction were assessed. Patients were followed up for 19.6+/-3.2 months. The results showed that the bulbocavernosus reflex elicited no response in either the sphincter or the bulbocavernosus muscle. Their activity, recorded by electromyography, as well as anal and bulbar pressures at rest and on voluntary squeeze, and electrostimulation of the external anal sphincter, showed a significant reduction compared to the controls. Sphincteroplasty made the patients continent and restored erectile function and ejaculation to normal. We conclude from the current study that the reduced activity of the bulbocavernosus muscle is probably caused by injury to the external anal sphincter. It is suggested that erectile dysfunction is caused by the failure, during erection, of the contraction of the bulbocavernosus muscle to raise cavernosal pressure above systolic blood pressure. The loss of the rhythmical contractions of the bulbocavernosus muscle is probably why ejaculation did not occur in jets. Repair of the external anal sphincter provided a cure for faecal incontinence and erectile dysfunction. Anorectal disorders are believed to affect erectile function, a relationship that needs further investigation.     

Anterior anal fissures are associated with occult sphincter injury and abnormal sphincter function

Objective The pathogenesis of chronic anal fissure (CAF) remains incompletely understood but most are associated with a high resting anal pressure and reduced perfusion at the fissure site. To date, no major distinction has been made between anterior and posterior anal fissures and their aetiology and treatment. We compared anterior and posterior fissures in patients who have failed to respond to medical treatment with respect to their underlying aetiology, anal canal pressures and sphincter muscle integrity. Method Seventy consecutive patients (54 female:16 male) with a symptomatic CAF and 39 normal controls (19 female:20 male) without evidence of significant ano‐rectal pathology were prospectively assessed by manometry and anal endosonography. Results Anterior anal fissures were identified in a younger age group [33 years (IQR 26–37) vs 41 years (IQR 36–52)] and predominantly in women. Anterior fissure patients were significantly more likely to have underlying external anal sphincter defects compared with posterior fissures [OR 10.9 (95% CI 3.4–35.4)]. Maximum resting pressure was not significantly elevated for anterior fissures compared with controls (P = 0.316) but was significantly elevated in posterior fissures (P = 0.005). The maximum squeeze pressure was significantly lower in the anterior fissure group [167 cmH₂O (IQR 126–196) vs 205 cmH₂O (IQR 174–262), P = 0.004]. A history of obstetric trauma was significantly associated with anterior fissure location [OR 13.9 (95% CI 3.4–55.7)]. Conclusions Anterior anal fissures are associated with occult external anal sphincter injury and impaired external anal sphincter function compared with posterior fissures. These findings have implications for treatment, especially if a definitive procedure, such as lateral internal sphincterotomy, is considered.     

Effect of micturition on the external anal sphincter: identification of the urethro-anal reflex

BACKGROUND/OBJECTIVE: A study on the response of the external anal sphincter (EAS) to the passage of urine through the urethra during micturition could not be found in the literature. We investigated the hypothesis that urine passage through the urethra effects EAS contraction to guard against possible flatus or stool leakage during micturition. METHODS: The study was performed in 23 healthy volunteers (age, 38.6 +/- 10.8 [SD] years; 14 men and 9 women). The EAS electromyogram (EMG) was performed during micturition by surface electrodes applied to the EAS. Also, the EAS EMG response to urethral stimulation by a catheter-mounted electrode was registered. The test was repeated after individual anesthetization of the EAS and urethra. RESULTS: The EAS EMG recorded a significant increase (P < 0.01) during micturition and on urethral stimulation at the bladder neck. Stimulation of the prostatic, membranous, or penile urethra produced no significant change in the EAS EMG. Urethral stimulation after individual EAS and urethral anesthetization did not cause any changes in the EAS EMG. CONCLUSIONS: Urine passing through the urethra or urethral stimulation at the vesical neck produced an increase in the EAS EMG, which presumably denotes EAS contraction, which seems to guard against flatus or fecal leakage during micturition. EAS contraction on urethral stimulation is suggested to be mediated through a urethro-anal reflex. Further studies on this issue may potentially prove the diagnostic significance of this reflex in micturition and defecation disorders.     

Electrically evoked activity in the human external anal sphincter

Following electrical stimulation of perianal skin, short latency evoked electromyographic (EMG) responses from the external and sphincter have been interpreted as the electrophysiological correlate of the anal reflex. Delayed responses in patients with idiopathic faecal incontinence have been interpreted as evidence for denervation of the external anal sphincter. Electrically evoked responses were studied in normal subjects, either before and during spinal anaesthesia (n = 8), or before and during competitive neuromuscular blockade (n = 4), instituted for operative purposes. Short latency responses persisted unchanged in either latency or duration during spinal anaesthesia whereas long latency responses were completely abolished. Both short and long latency responses were abolished during competitive neuromuscular blockade. Short latency responses are not spinal reflex in nature, but due to stimulus activation of alpha-motoneuronal terminal branches. Delayed responses in incontinent patients cannot be interpreted as evidence for pudendal neuropathy. Long latency (i.e. greater than 40 ms) responses demand a functional sacral spinal cord and represent the true anal reflex. Their wide range of latency in normal subjects suggests this measurement will be of little use in confirming the presence or absence of pudendal neuropathy, and that other measures of neuropathy may be more appropriate.     

肛门括约肌损伤的诊治

肛直肠环亦称耻骨直肠环,是肛管与直肠连接处括约肌群的总称。由耻骨直肠肌、肛管内括约肌、直肠壁纵肌下部、肛管外括约肌的深部和邻近的部分肛提肌纤维等几乎全部肛管直肠的肌肉组成,对排控便起重要作用,其中耻骨直肠肌是维持肛门自制的关键性肌肉。各种原因导致此环不完整,均可引起大便失禁。一、肛门括约肌损伤的常见原因1.外伤:由于车祸、高空坠落伤等原因导致的肛门括约肌损伤近年来呈上升趋势。此类患者多合并有骨盆骨折、会阴部严重的撕裂伤,常因患者有意识障碍、疼痛剧烈、伤口位于直肠肛管内等原因易于漏诊。2.产伤:多见于经阴道…     

Effect of external anal sphincter contraction on the ischiocavernosus muscle and its suggested role in the sexual act

Whereas the bulbocavernosus muscle shares its contractile activity with the external anal sphincter (EAS), the response of the ischiocavernosus muscle (ICM) to EAS contraction could not be traced in the literature. We investigated the hypothesis that the ICM contracts reflexly upon EAS contraction. The response of the ICM to EAS squeeze and stimulation was recorded in 21 healthy volunteers (13 men, 8 women, age 36.8 +/- 10.7 [SD] years). An electromyographic (EMG) needle (stimulating) electrode was introduced into the EAS and another (recording) one was inserted into the ICM. The test was repeated after individual anesthetization of the EAS and ICM and after muscle infiltration with normal saline instead of lidocaine. EAS electrostimulation (10 stimuli, 200 micros duration, 0.2 Hz frequency, 0-100 mA intensity) produced an increase of ICM EMG activity to a mean of 267.8 +/- 42.7 microV, whereas anal squeeze effected an increase to a mean of 224.5 +/- 45.3 microV. The ICM did not respond to stimulation of the EAS after individual anesthetization of the ICM and EAS, but it did after saline infiltration. The results were reproducible. ICM contracted upon EAS contraction. This effect seems to be mediated through a reflex that we call "anocavernosal excitatory reflex." The ICM lever action is suggested to share in the erectile mechanism by elevating the penile shaft to above the horizontal level. The reflex may prove of diagnostic significance in sexual function disorders, a point that needs further study.     

Neural electrophysiological studies on the external anal sphincter in children with anorectal malformation

BACKGROUND/PURPOSE: Abnormality of innervation of external anal sphincter is one of the most important factors affecting postoperative anorectal function. The abnormalities of lumbosacral nerves have been reported in many radiological and histopathologic studies. There are few reports on the neurophysiological changes in children with anoractal malformation. The aim of this study was to examine the functional changes of nerves to the external anal sphincter in anorectal malformation. METHODS: Forty-five patients with anorectal malformation underwent studies of latencies of pudendo-anal reflex, spinoanal response, and evoked potential of cauda equine simultaneously. The conduction time of afferent nerve, efferent nerve, and sacral spinal center of pudendo-anal reflex arc were analyzed quantitatively. RESULTS: The latencies of pudendo-anal reflex, spino-anal response, and conduction time of sacral spinal center significantly are prolonged in patients with anorectal malformation (P< .05). There was significant difference between rectourethral fistula group and vestibular fistula group as well as low-type deformity group. The patients with lumbosacral anomalies such as lumbosacral spinal bifida or absence of S4 or S5 had prolonged latencies, especially the pudendo-anal reflex latency. There was significant negative correlation between the latencies and clinical scores. Although pudendoanal reflex latency was longer in patients who had posterior sagittal anorectoplasty than those who had abdominoperineal pull-through procedure, the difference was not significant. CONCLUSIONS: The abnormality of nerves to external anal sphincters is one of the important causes for clinical outcome. The neural lesions vary in each type of anal and lumbosacral deformity.     

Neural control of internal anal sphincter function

The effect on anal tone of electrical stimulation of the presacral (hypogastric) sympathetic nerves has been studied in eight patients during abdominal rectopexy or restorative proctocolectomy. A sharp fall in anal pressure occurred in seven patients (mean fall 59 cmH2O; range 35-80 cmH2O). In one patient given a beta- and alpha-sympathetic blocking drug (labetalol 200 mg) intra-operatively, the anal pressure decreased by 15 cmH2O. These observations show that stimulation of the presacral sympathetic nerves causes relaxation of the internal anal sphincter and implies that these nerves may induce relaxation of the sphincter in vivo. The pathway of the recto-anal reflex has been studied intra-operatively in three patients undergoing rectal excision. The recto-anal reflex is present after presacral nerve blockade and after full mobilization of the rectum, but is abolished by circumferential rectal myotomy. The reflex has a local intramural pathway. This observation validates the assumption that absence of this reflex is a feature of aganglionosis, as in Hirschsprung's disease.