Compound muscle action potential of the external anal sphincter

AIM

Pudendal nerve terminal motor latency (PNTML) assesses distal innervation of the external anal sphincter (EAS) but it is insensitive to early nerve damage. We propose to extend the assessment of PNTML to the measurement of the compound muscle action potential (CMAP) of the EAS to understand its progressive denervation.

METHOD

Ninety women with faecal incontinence were prospectively examined and compared with 36 asymptomatic women who acted as controls. PNTML was performed bilaterally and the muscle response analysed for CMAP to include amplitude, area and duration. Anorectal manometry was measured by a station-pull technique using a water-filled microballoon. spss version 11.5 was used for statistical analysis.

RESULTS

In asymptomatic women the CMAP on the left side was greater in nulliparous (n = 7) than parous (n = 27, P < 0.05) individuals. There was a positive correlation with maximum squeeze pressure and area on the left side (P < 0.05, r = 0.397). In women with faecal incontinence, CMAP on the left side had a negative correlation with age (n = 75, P < 0.05), there was no correlation with parity or anorectal manometry. Nulliparous asymptomatic women had a greater CMAP (P < 0.05) on the left side than asymptomatic parous women and parous women with faecal incontinence. Right-side measurements were not conclusive.

CONCLUSION

Compound muscle action potential demonstrated progressive denervation with age in women with faecal incontinence but did not reliably identify early signs of denervation in asymptomatic women. The area on the left side related to muscle function in asymptomatic women but not in women with faecal incontinence. CMAP can distinguish between parous women with faecal incontinence and nulliparous asymptomatic women but is not a useful test of function of the EAS.

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 cmH(2) O/min) were less susceptible to fatigue than women with normal bowel control (n=36, median -43 cmH(2) O/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.

Investigation of stimulus position in the production of the strength duration curve of the external anal sphincter muscle in women with anorectal dysfunction

OBJECTIVE

The strength duration test (SDT) is a minimally invasive test of the innervation of a muscle and has been successfully adapted for use on the external anal sphincter (EAS). The SDT has previously been performed on the EAS placing a stimulating probe in the 3 o'clock position. The aim of this study was to determine whether there was any variation in the strength duration curves (SDC) produced at different positions around the EAS.

PATIENTS AND METHODS

Thirty-one patients with anorectal dysfunction attended our Institution for Anorectal Physiology Studies and were recruited to the study. After undergoing anal manometry, pudendal nerve terminal motor latency measurement and endoanal ultrasonography, the SDT was performed in four stimulus positions (3, 6, 9 and 12 o'clock). The sequence of positions was randomly selected.

RESULTS

Four SDCs were obtained successfully in 25 patients. There was no significant difference seen between the four positions at the longer current durations (1-100 ms). Significant differences occurred at the shortest current durations (0.3 and 0.1 ms) when comparing adjacent stimulus positions except between the 6 and 9 o'clock positions, which were comparable. When opposing positions were compared (3-9 and 6-12 o'clock) at these short durations no significant difference was found.

CONCLUSION

There was no significant difference between the SDC produced at 3 and 9 o'clock. These positions closely correspond to where the pudendal nerves enter the EAS. It therefore appears acceptable to perform the SDT in either of these positions, though 3 o'clock remains our preferred position.

A valsalvometer can be effective in standardising the Valsalva manoeuvre

A prospective randomised controlled study was performed in order to study the effectiveness of a device designed to reduce the variability in intra-abdominal pressures generated by individuals performing the Valsalva manoeuvre. One hundred women were recruited to take part in the project which compared a traditional Valsalva manoeuvre following standardised verbal instruction with forced expiration through a flow restriction device called a "valsalvometer". The abdominal pressure was measured using an air-filled rectal balloon catheter linked to a pressure transducer. The use of the valsalvometer was associated with a reduction in variation of intra-abdominal pressure between women to 50% of the standard deviation. The new device has the capacity to reduce the variation in intra-abdominal pressure produced when performing the Valsalva manoeuvre. The rise in intra-abdominal pressure may act as a standard against which other measurements are made.

Routine symptom screening for postnatal urinary and anal incontinence in new mothers from a district

Parous middle-aged women present with urinary and faecal incontinence and childbirth trauma is thought to be a causal factor. Both symptoms are common after childbirth but usually go under-reported. It has been suggested that new mothers are likely to benefit from routine symptom screening because by actively identifying symptomatic women they could then be helped to access continence services. The main objective of this study was to pilot a programme of routine symptom screening for postnatal urinary and anal incontinence in new mothers from a district general hospital. Self-completion questionnaires for both urinary and anal incontinence were sent by post to 442 primiparous women who had delivered consecutively 10 months previously in a district general hospital. Two hundred and seventy-five new mothers responded to the survey. Ninety-two women had new symptoms of incontinence at 10 months, 82 had urinary incontinence and 25 had anal incontinence. However, only six new mothers had discussed the problem with a health professional. Although nine women requested a hospital appointment none of the women attended the appointment arranged for them. The domain scores on both questionnaires were significantly less for symptomatic new mothers when compared to women with established symptoms of incontinence. The programme of screening successfully identified women with symptoms of incontinence. However, all of the symptomatic women declined a follow-up appointment at hospital which questions the benefits of routine screening 10 months after childbirth.

The strength duration test: a novel tool in the identification of occult neuropathy in women with pelvic floor dysfunction

OBJECTIVE

The Strength-duration test (SDT) is a simple minimally invasive measure of muscle innervation, recently adapted for the assessment of the external anal sphincter (EAS). This test can discriminate women with faecal incontinence from controls. The purpose of this study was to determine if the SDT could detect denervation of the EAS in women with weak but anatomically intact EAS and normal pudendal nerve terminal motor latency (PNTML).

PATIENTS AND METHODS

Thirteen women with weak but intact EAS on endoanal ultrasound (EAUS) with normal maximum resting pressure and PNTML were recruited to undergo the SDT. The results from this group were compared to control data for the SDT previously collected in our unit.

RESULTS

Nine of 13 women were found to have SDT above a 95% confidence interval of the mean curve for controls and six had a SDT outside a 90% confidence interval for individuals derived from control data, suggesting denervation of the EAS. The mean area under the curve was significantly higher in our study group compared to controls (91.0 microsmA vs 72.2 microsmA, P = 0.047) as was the current intensity measured at the 1 ms pulse duration (18.2 mA vs 12.94 mA, P = 0.048), typical of denervation with this test.

CONCLUSION

The SDT was abnormal in nine of the 13 study patients. This may partly explain reduced maximum voluntary contraction seen in this group of patients. SDT may be a more sensitive tool in detecting neuropathy than latency measurement.

Fatigability of the external anal sphincter in anal incontinence

INTRODUCTION

Anal incontinence commonly results from external anal sphincter dysfunction. The muscle is routinely assessed by anorectal physiology studies. Fatigability is not routinely measured but should be an important factor in the maintenance of continence. The fatigue rate index has been developed to address this. The purpose of this study was to investigate the fatigability of the external anal sphincter in incontinent patients compared with that in controls and to determine its correlation with symptom severity and pudendal nerve terminal motor latency measurement.

METHODS

Forty-two patients with anal incontinence (33 female, 9 male) and 20 control patients (17 female, 3 male) were studied. As part of anorectal physiology studies, manometry was measured by a station pull-through technique with a closed-system microballoon. After a rest period of one minute, fatigue was measured over a 20-second squeeze at 1.5 cm in the anal canal with two consecutive readings separated by a further one-minute rest period. The fatigue rate index was calculated from the maximum squeeze pressure and fatigue rate. A validated symptom severity scoring system was used to assess symptomatology in patients with anal incontinence.

RESULTS

No difference was detected in demographic factors between the two groups. The fatigue rate index was significantly different between the control and incontinent groups (1.85 vs. 0.67 minutes, P = 0.001). No other factors were significantly different between the two groups (maximum squeeze pressure, 89.1 vs. 79 cm H(2)O, P = 0.42; fatigue rate, -85.8 vs. -101.2 cm H(2)O/min, P = 0.62). The fatigue rate index demonstrated a significant correlation with symptom score ( r = -0.44, P = 0.005). The fatigue rate index did not correlate with latency measurement.

CONCLUSIONS

A significant difference was detected in the fatigue rate index between incontinent and control patients. The Fatigue Rate Index demonstrated a significant correlation with symptom severity score and it may be a useful discriminating measure of external anal sphincter function.

Strength-duration testing of the external anal sphincter in females with anorectal dysfunction

PURPOSE

The strength-duration test has been suggested as a means of assessing external anal sphincter function. This study was designed to investigate this claim by comparing the strength-duration test with established measures of external anal sphincter function.

METHODS

Forty-nine females undergoing diagnostic anorectal testing (manometry, rectal sensation, electromyogram, pudendal nerve terminal motor latency, and endoanal ultrasound) also had the strength-duration test performed (which was repeated for each patient after a short rest period).

RESULTS

The strength-duration test was repeatable. Statistically significant correlations were found between this test at pulse durations of 3 ms, 1 ms, and 0.3 ms with electromyographic activity of the external anal sphincter and with pressure in the anal canal during voluntary contraction. Significant correlations were found for durations of 100 ms, 30 ms, 10 ms, and 3 ms with the pudendal nerve terminal motor latency on the right and for the 3 ms and 0.3 ms durations with latency on the left. There were no correlations between the strength-duration test and resting pressure in the anal canal.

CONCLUSION

The strength-duration test significantly correlates with the established measures of external anal sphincter function and its innervation. Therefore, this simple test appears to provide a simple measure of external anal sphincter denervation.

Urodynamic services, personnel and training in the United Kingdom

OBJECTIVE

To audit the provision of urodynamic services in the UK, with particular emphasis on the personnel involved and the training they received.

METHODS

A questionnaire was sent to 163 centres carrying out urodynamics in the UK asking for information on the department providing the service, the frequency of use, the number of patients investigated, professional training of the personnel and whether the personnel thought that the training was adequate.

RESULTS

Most urodynamic facilities in the UK function on a part-time basis. Urodynamics are carried out by a variety of healthcare professionals but most are performed by doctors and nurses. Half the respondents considered the training to be inadequate.

CONCLUSION

Consideration should be given to requiring a minimum standard of training for personnel carrying out urodynamics in the UK to ensure that a quality service is provided.

Validation of a non-invasive radioisotope method of imaging ureteric urine transport

Measurement of ureteric function has hitherto involved the use of invasive techniques. A non-invasive, radioisotope method of imaging and displaying individual ureteric boluses has been described, a refinement of which is used in this department. Each "spindle" displayed using this technique theoretically represents an individual ureteric bolus of urine, but the technique has never been validated in the normal ureter in either the experimental model or man. A porcine model was set up to allow simultaneous measurement of ureteric bolus transmission using the radioisotope (compressed image) method and by the accepted techniques of electromyography (EMG) and urine drop counting. The timing of each urinary bolus, as recorded by the different modalities was then compared. The results from 11 studies showed a significant correlation between the radioisotope and EMG methods (mean r = 1.00, P = 0.0003). There was a constant relationship between the part of the radioisotopic image representing the rear end of the bolus and the EMG complex (mean time difference = 5.32 +/- 1.067s), thus defining that part of the image representing the peristaltic contraction wave. There was a variable relationship between the EMG and the part of the image representing the leading edge of the bolus (mean time difference = 13.36 +/- 5.23s), emphasising that bolus length is variable, being dependent on bolus volume. The radioisotope "spindle" concurs with EMG activity in the porcine ureter. The compressed image technique is thus validated as a non-invasive method of demonstrating ureteric urine transport.

Pelvic floor damage and childbirth: a neurophysiological study

Ninety six nulliparous women were investigated to establish whether childbirth causes damage to the striated muscles and nerve supply of the pelvic floor. The techniques used were concentric needle electromyography (EMG), pudendal nerve conduction tests and assessment of pelvic floor contraction using a perineometer. There was EMG evidence of re-innervation in the pelvic floor muscles after vaginal delivery in 80% of those studied. Women who had a long active second stage of labour and heavier babies showed the most EMG evidence of nerve damage. Forceps delivery and perineal tears did not affect the degree of nerve damage seen. We conclude that vaginal delivery causes partial denervation of the pelvic floor (with consequent re-innervation) in most women having their first baby. In a few this is severe and is associated with urinary and faecal incontinence. For some it is likely to be the first step along a path leading to prolapse and/or stress incontinence.

The role of pudendal nerve damage in the aetiology of genuine stress incontinence in women

Conduction was studied in the terminal branches of the pudendal nerve in 42 women with normal urinary control and 87 women with stress incontinence of urine, genitourinary prolapse, or both. Women with stress incontinence of urine had delayed conduction to both the striated urethral muscle and the pelvic floor muscle, indicative of denervation injury. Women with normal urinary control and genitourinary prolapse had similar conduction times to the urethral sphincter striated muscle as normal women but clear evidence of denervation damage to the pelvic floor.

The role of partial denervation of the pelvic floor in the aetiology of genitourinary prolapse and stress incontinence of urine. A neurophysiological study

Single-fibre electromyography of the pubococcygeus muscle of the pelvic floor was performed in 69 asymptomatic women and 105 women with stress incontinence of urine or genitourinary prolapse or both. The results suggest that partial denervation of the pelvic floor with subsequent reinnervation is a normal accompaniment of ageing and is increased by childbirth. Women with stress incontinence of urine or genitourinary prolapse or both have a significant increase in denervation of the pelvic floor compared with asymptomatic women.

The anisotropic nature of urethral occlusive forces

A newly-developed unidirectional force gauge was used to demonstrate that the urethral occlusive forces are unequal around the circumference of the female urethra. In the proximal two-thirds of the urethra significantly greater forces are exerted in the anterior position compared with those exerted in the lateral and posterior positions. By contrast the occlusive forces in the distal third of the urethra are greater in the posterior and lateral positions than in the anterior position. These findings hold true for both women with normal and abnormal urinary control. Rotational variations have previously been reported but have been thought to be artefact due to catheter stiffness; this study shows that rotational variations are genuine and not due to artefact.

A uni-directional urethral force gauge

Until now urethral transducers have had poor circumferential resolution and have been inadequate for assessing whether the forces closing the female urethra are equally distributed around its circumference or whether they are greater in some directions than others. This paper describes a urethral force gauge which is capable of measuring urethral occlusive forces in a uni-directional manner because it is sensitive to forces around only 20 degrees of the urethral circumference. The gauge comprises a sensor, utilising two semi-conductor strain gauges, mounted at the tip of a 14 F silicone rubber catheter. It has been used in the investigation of 232 female patients and has proved to be reliable and robust.