Anal-sphincter disruption during vaginal delivery

BACKGROUND

Lacerations of the anal sphincter or injury to sphincter innervation during childbirth are major causes of fecal incontinence, but the incidence and importance of occult sphincter damage during routine vaginal delivery are unknown. We sought to determine the incidence of damage to the anal sphincter and the relation of injury to symptoms, anorectal physiologic function, and the mode of delivery.

METHODS

We studied 202 consecutive women six weeks before delivery, 150 of them six weeks after delivery, and 32 with abnormal findings six months after delivery. Symptoms of anal incontinence and fecal urgency were assessed, and anal endosonography, manometry, perineometry, and measurement of the terminal motor latency of the pudendal nerves were performed.

RESULTS

Ten of the 79 primiparous women (13 percent) and 11 of the 48 multiparous women (23 percent) who delivered vaginally had anal incontinence or fecal urgency when studied six weeks after delivery. Twenty-eight of the 79 primiparous women (35 percent) had a sphincter defect on endosonography at six weeks; the defect persisted in all 22 women studied at six months. Of the 48 multiparous women, 19 (40 percent) had a sphincter defect before delivery and 21 (44 percent) afterward. None of the 23 women who underwent cesarean section had a new sphincter defect after delivery. Eight of the 10 women who underwent forceps delivery had sphincter defects, but none of the 5 women who underwent vacuum extractions had such defects. Internal-sphincter defects were associated with a significantly lower mean (+/- SD) resting anal pressure (61 +/- 11 vs. 48 +/- 10 mm Hg, P < 0.001) six weeks post partum, and external-sphincter defects were associated with a significantly lower squeeze pressure (increase above resting pressure, 70 +/- 38 vs. 44 +/- 13 mm Hg; P < 0.001). There was a strong association (P < 0.001) between sphincter defects and the development of bowel symptoms.

CONCLUSIONS

Occult sphincter defects are common after vaginal delivery, especially forceps delivery, and are often associated with disturbance of bowel function.

Injury to innervation of pelvic floor sphincter musculature in childbirth

71 women delivered at St Bartholomew's Hospital, London, were studied by electrophysiological tests of the innervation of the external anal sphincter muscle and by manometry. The investigations were done 2-3 days after delivery and again, in 70% of these women, 2 months later. Faecal and urinary incontinence developing after vaginal delivery has been thought to be due to direct sphincter division, or muscle stretching, but the results of the study suggest that in most cases this incontinence results from damage to the innervation of the pelvic floor muscles.

Electrical stimulation of sacral spinal nerves for treatment of faecal incontinence

Functional deficits of the striated anal sphincteric muscles without any apparent gross defect often result in a lack of ability to postpone defaecation by intention or in faecal incontinence in response to increased intra-abdominal or intra-rectal pressure. We applied electrostimulation to the sacral spinal nerves to increase function of the striated muscles of the anal sphincter. Of three patients followed for 6 months, two gained full continence and one improved from gross incontinence to minor soiling. Closure pressure of the anal canal increased in all. Preliminary data indicate that anal closure pressure increases with the duration of stimulation. Continuous stimulation of sacral spinal nerves can help some patients with faecal incontinence. It may be possible to promote continence with intermittent stimulation.

Sphincter denervation in anorectal incontinence and rectal prolapse

Biopsies of the external anal sphincter, puborectalis, and levator ani muscles have been examined in 24 women and one man with long-standing anorectal incontinence, 18 of whom also had rectal prolapse, and in two men with rectal prolapse alone. In 16 of the women anorectal incontinence was of unknown cause, but in eight there was a history of difficult labour. Similar biopsies were examined in six control subjects. In all the incontinent patients there was histological evidence of denervation, which was most prominent in the external anal sphincter muscle biopsies, and least prominent in the levator ani muscles. Myopathic features, which were thought to be secondary, were present in the more abnormal biopsies. There were severe histological abnormalities in small nerves supplying the external anal sphincter muscle in the three cases in which material was available for study. We suggest that idiopathic anorectal incontinence may be the result of denervation of the muscles of the anorectal sling, and of the anal sphincter mechanism. This could result from entrapment or stretch injury of the pudendal or perineal nerves occurring as a consequence of rectal descent induced during repeated defaecation straining, or from injuries to these nerves associated with childbirth.

Slowed conduction in the pudendal nerves in idiopathic (neurogenic) faecal incontinence

We have studied 30 patients with idiopathic (neurogenic) faecal incontinence using anorectal manometry and concentric needle and single fibre electromyographic methods. We have measured the terminal motor latency in the pudendal nerves of these patients using a new digitally directed transrectal stimulation and recording technique (right mean (+/- s.d.) 3.2 +/- 0.9 ms, left mean (+/- s.d.) 3.0 +/- 0.9 ms) and compared the results with those obtained from 28 normal subjects (right mean (+/- s.d.) 2.0 +/- 0.5 ms, left mean (+/- s.d.) 1.9 +/- 0.3 ms). These differences between normal and incontinent patients were significant (P = 0.01) using the Wilcoxon Rank Sum Test. The findings support the hypothesis that idiopathic (neurogenic) faecal incontinence is due to damage to the nerve supply of the pelvic floor musculature.

Physiological studies of the anal sphincter musculature in faecal incontinence and rectal prolapse

The clinical, anorectal manometric and electrophysiological findings in 24 patients with faecal incontinence, 10 of whom also had rectal prolapse, and in 8 patients with rectal prolapse without incontinence, are reported. Single fibre electromyographic studies and anal reflex latencies were abnormal, indicating damage to the innervation of the pelvic floor musculature, in all the patients with faecal incontinence, with or without rectal prolapse. These studies were normal in 7 of the 8 patients in whom rectal prolapse occurred without incontinence. These investigations imply that denervation of the sphincter musculature can be recognized by electrophysiological tests in most patients with primary faecal incontinence and that the pathogenesis of rectal prolapse differed in the two groups of patients.

Risk factors in childbirth causing damage to the pelvic floor innervation

The innervation of the pelvic floor musculature is damaged in both stress urinary incontinence and idiopathic (neurogenic) anorectal incontinence. Because childbirth has been considered to be a causative factor in stress incontinence we have assessed the effect of childbirth on the innervation of the pelvic floor musculature in 122 consecutively referred women. They were investigated 48-72 h and 2 months after delivery; 51 were also studied 6 months prior to delivery. In 45 of these 51 women delivered vaginally, EMG studies of the external anal sphincter muscle showed that the fibre density (FD) increased from 1.38 +/- 0.14 before delivery to 1.57 +/- 0.19 2 months after delivery (p less than 0.01). There was no change in the FD in the external anal sphincter muscle after delivery in 20 women delivered by Caesarean section. The pudendal nerve terminal motor latency (PNTML) measured 48-72 h after delivery was increased in the 102 women delivered vaginally compared to 34 nulliparous control subjects. Analysis of the whole group of 122 women showed that multiparity, forceps delivery, increased duration of the second stage of labour, third degree perineal tear and high birth weight were important factors leading to pudendal nerve damage. Epidural anaesthesia had no effect on pudendal nerve function. Modification of these obstetric risk factors may ultimately reduce the frequency of stress urinary and faecal incontinence in women.

Increased motor unit fibre density in the external anal sphincter muscle in ano-rectal incontinence: a single fibre EMG study

The motor unit fibre density in the external anal sphincter muscle has been measured in 13 normal subjects aged 18 to 78 years, and in 14 patients with ano-rectal incontinence, aged 17 to 72 years. The mean fibre density in the normal subjects was 1.5 +/- 0.16, and in the incontinent subjects it was 2.17 +/- 0.28 (p less than 0.001). These findings provide support for the suggestion that ano-rectal incontinence commonly has a neurogenic basis.

Pathophysiology of adult fecal incontinence

Fecal incontinence occurs when the normal anatomy or physiology that maintains the structure and function of the anorectal unit is disrupted. Incontinence usually results from the interplay of multiple pathogenic mechanisms and is rarely attributable to a single factor. The internal anal sphincter (IAS) provides most of the resting anal pressure and is reinforced during voluntary squeeze by the external anal sphincter (EAS), the anal mucosal folds, and the anal endovascular cushions. Disruption or weakness of the EAS can cause urge-related or diarrhea-associated fecal incontinence. Damage to the endovascular cushions may produce a poor anal "seal" and an impaired anorectal sampling reflex. The ability of the rectum to perceive the presence of stool leads to the rectoanal contractile reflex response, an essential mechanism for maintaining continence. Pudendal neuropathy can diminish rectal sensation and lead to excessive accumulation of stool, causing fecal impaction, mega-rectum, and fecal overflow. The puborectalis muscle plays an integral role in maintaining the anorectal angle. Its nerve supply is independent of the sphincter, and its precise role in maintaining continence needs to be defined. Obstetric trauma, the most common cause of anal sphincter disruption, may involve the EAS, the IAS, and the pudendal nerves, singly or in combination. It remains unclear why most women who sustain obstetric injury in their 20s or 30s typically do not present with fecal incontinence until their 50s. There is a strong need for prospective, long-term studies of sphincter function in nulliparous and multiparous women.

Scope of a technique for electrical stimulation of human brain, spinal cord, and muscle

Brief high-voltage electrical shocks from a special low-output-resistance stimulator, delivered through electrodes on the skin, can excite human muscle directly (not by way of the nerves) and can also excite the motor cortex, the visual cortex, and the spinal cord. Possible applications of the technique include measurement in muscle disorders of the latency relaxation and of the excitability and contractility of muscle without the interposition of nerve fibres or the neuromuscular junction; measurement of conduction velocity in the pyramidal tract; and the detection of neuropathy in the nerves to the external sphincter ani.

Manometric tests of anorectal function in healthy adults

OBJECTIVE

Although tests of anorectal function are useful in the assessment of defecation disorders, there is inadequate and inconsistent information regarding normative data. Also, there are discrepancies in manometric techniques and data interpretation. Our aim was to perform a comprehensive evaluation of anorectal function in healthy adults.

METHODS

We used a 6-mm diameter probe containing six radially arrayed microtransducers, and a 4-cm-long latex balloon for performing anorectal manometry in 45 healthy subjects who were controlled for gender and age. Sequentially, subjects were asked to squeeze, bear down, or blow up a party balloon. Subsequently, rectal sensation, rectal compliance, and rectoanal reflexes were assessed simultaneously by performing intermittent phasic balloon distentions. Additionally, balloon defecation, pudendal nerve latency, and saline continence tests were performed.

RESULTS

In men, the anal sphincter was longer (p < 0.05) and squeeze sphincter pressure and squeeze duration were higher (p < 0.01), but resting sphincter pressure was similar to that in women. When bearing down, although not significant, the defecation index was higher in men. Distinct thresholds for rectal sensation were identified but there was no gender difference. Likewise, rectal compliance and balloon expulsion time were similar. However, during saline infusion, the onset of first leak and total volume retained were higher (p < 0.001) and pudendal nerve latency was shorter (p < 0.05) in men. Overall, parity or age did not influence anorectal function.

CONCLUSIONS

This study represents the most comprehensive age- and gender-controlled assessment of anorectal function using solid state technology. Gender influences some parameters of anorectal function. Our results could serve as a valuable resource of normative data.

Effects of short term sacral nerve stimulation on anal and rectal function in patients with anal incontinence

BACKGROUND

Some patients with faecal incontinence are not amenable to simple surgical sphincter repair, due to sphincter weakness in the absence of a structural defect.

AIMS

To evaluate the efficacy and possible mode of action of short term stimulation of sacral nerves in patients with faecal incontinence and a structurally intact external anal sphincter.

PATIENTS

Twelve patients with faecal incontinence for solid or liquid stool at least once per week.

METHODS

A stimulating electrode was placed (percutaneously in 10 patients, operatively in two) into the S3 or S4 foramen. The electrode was left in situ for a minimum of one week with chronic stimulation.

RESULTS

Evaluable results were obtained in nine patients, with early electrode displacement in the other three. Incontinence ceased in seven of nine patients and improved notably in one; one patient with previous imperforate anus and sacral agenesis had no symptomatic response. Stimulation seemed to enhance maximum squeeze pressure but did not alter resting pressure. The rectum became less sensitive to distension with no change in rectal compliance. Ambulatory studies showed a possible reduction in rectal contractile activity and diminished episodes of spontaneous anal relaxation.

CONCLUSIONS

Short term sacral nerve stimulation notably decreases episodes of faecal incontinence. The effect may be mediated via facilitation of striated sphincter muscle function, and via neuromodulation of sacral reflexes which regulate rectal sensitivity and contractility, and anal motility.

Obstetric damage and faecal incontinence

Anal incontinence for gas or faeces affects up to 11% of adults, and occurs frequently in 2%. The commonest cause in healthy women is unrecognised damage to the anal sphincter during childbirth; 13% of women having their first vaginal delivery develop incontinence or urgency, and 30% have structural changes shown by anal endosonography. The commonest predisposing cause of damage is the use of forceps. When a third-degree tear occurs, 85% of women have persistent structural sphincter defects and 50% remain symptomatic despite primary repair after delivery. Structural damage associated with childbirth is more important than neurological factors. The characterisation of this sphincter damage has led to improved treatment, including successful surgical repair.

The pelvic floor musculature in the descending perineum syndrome

We have studied 20 patients with the descending perineum syndrome, half of whom were incontinent of faeces. Objective criteria were established in 103 control subjects for determining the relationship of the perineum to the bony pelvis. The anal reflex latency was increased in the 10 patients in whom perineal descent was associated with faecal incontinence, but not in the 10 without incontinence. However, there was hypertrophy of the muscle fibers in external anal sphincter muscle biopsies in all the patients. Thus, abnormal degrees of perineal descent are associated with changes in the external anal sphincter muscle, consistent with damage to its nerve supply.

Characterization of mechanosensitive pelvic nerve afferent fibers innervating the colon of the rat

1. Single-unit activity was recorded from S1 sacral dorsal root afferent fibers in the anesthetized rat. A total of 364 afferent fibers were identified by electrical stimulation of the pelvic nerve and subsequently tested for response to colorectal distension (CRD) and urinary bladder distension (UBD). Sixty-seven percent (n = 244) of the fibers were unmyelinated C-fibers and 33% (n = 120) were thinly myelinated A delta-fibers. 2. In three initial experiments, 35 fibers were identified by pelvic nerve stimulation and tested for response only to CRD; none of these fibers responded to CRD. In 20 subsequent experiments, 329 pelvic nerve afferent fibers were tested for response to CRD and UBD. Thirty-four percent (n = 112) of the 329 fibers were unresponsive to noxious CRD (80 mmHg) or to UBD (slow filling < or = 100 mmHg), 44% (n = 146) responded to UBD, 16% (n = 53) responded to CRD, and 6% (n = 18) responded to mechanical stimulation of the anal mucosa. 3. Of the total of 53 pelvic nerve afferent fibers that responded to CRD, 43 (81%) were C-fibers (mean: 1.5 m/s) and 10 (19%) were A delta-fibers (mean: 4.7 m/s). Fifteen of the CRD-sensitive fibers had no resting activity, whereas 38 fibers exhibited some resting activity (mean: 2.6 imp/s). 4. Reproducibility of responses to repeated CRD (80 mmHg, 30s, 10 trials at 4-min intervals) was tested in 17 fibers. In 16, responses to repeated distension were reproducible without evidence of facilitation or inhibition of subsequent responses. One fiber gave greater responses during the 9th and 10th trials. 5. Responses to graded CRD were studied in 44 fibers. All fibers exhibited monotonic, increasing stimulus-response functions < or = 80 mmHg of distension. Thresholds for response of the 44 fibers were determined after extrapolation of the least-squares linear-regression line to the ordinate and varied between 0 and 40 mmHg. Two populations of pelvic nerve afferent fibers in the colon were apparent: low threshold (LT) afferent fibers had a mean threshold of 2.9 mmHg (range: 0-10 mmHg; n = 34) and high threshold (HT) afferent fibers had a mean threshold of 32.6 mmHg (range: 28.0-40.0 mmHg; n = 10). 6. Chemosensitivity to bradykinin (BK) was tested in nine LT fibers. Seven fibers responded to BK (0.1 to 100 micrograms/kg ia) and two fibers did not respond up to 100 micrograms/kg of BK. Responses to BK tested in three fibers were dose dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Physiological and clinical outcome of anterior sphincteroplasty

A total of 55 women underwent sphincteroplasty for the treatment of faecal incontinence related to anterior defects. Patients were followed prospectively for a mean of 29 months to evaluate the outcome overall and according to age. All patients were evaluated clinically by means of a questionnaire and graded using an incontinence scoring system ranging from 0 (perfect continence) to 20 (complete incontinence). Some 52 patients (95 per cent) had had a previous vaginal delivery and 30 (55 per cent) had a history of previous anal sphincter repair. Physiological and functional parameters in patients with a successful outcome (n = 39) were compared with those in patients with a poor outcome (n = 16). The results were also compared in patients under (n = 39) and over (n = 16) 60 years of age. Overall, patients with a successful outcome had a significant change in mean and maximal resting and squeeze pressures. These changes correlated well with the increase in the high-pressure zone (HPZ) length from 1.0-2.2 cm (P = 0.0002) and with functional outcome (change in incontinence score from 15.3 to 5.8; P < 0.0001). In patients over 60 years of age, a significant change in mean squeeze pressure (P = 0.03) and HPZ length (P = 0.01) was noted and correlated with functional outcome (change in incontinence score from 14.3 to 6.4; P < 0.0001). A successful outcome after anterior sphincteroplasty is related to improvement in sphincter function even in an older population. These results demonstrate that age itself does not seem to be a predictor of poor outcome. Patients should not be denied a repair exclusively on grounds of age.

Effects of aging on the anorectal sphincters and their innervation

The effects of aging on the pelvic floor musculature and its innervation are described in 102 women and 19 men without colorectal or pelvic floor disease. In the women, a reduction in anorectal "squeeze" pressure was found in the fifth decade, but the resting anal pressure remained unchanged. This reduction in squeeze anal pressure was accompanied by an increase in the mean pudendal nerve terminal motor latency, indicating damage to this nerve, and increased perineal descent in the resting and straining positions. The fiber density, recorded by single fiber electromyography in the external anal sphincter muscle, a muscle innervated by the pudendal nerves, was increased in the sixth decade, indicating the later development of compensatory reinnervation in this muscle. The interrelation of aging, menopausal effects, and parity in these changes is difficult to define from currently available data, but the authors suggest, from other evidence, that menopausal effects may be relevant.

Pathogenesis of fecal incontinence in diabetes mellitus: evidence for internal-anal-sphincter dysfunction

We studied 16 patients with diabetes and fecal incontinence. The onset of incontinence coincided with the onset of chronic diarrhea in most patients. Episodes of incontinence occurred when stools were frequent and loose; however, 24-hour stool weights were usually within normal limits. All patients had evidence of autonomic neuropathy, and one third had steatorrhea. Incontinent diabetics had a lower mean basal anal-sphincter pressure than 35 normal subjects (63 +/- 4 vs. 37 +/- 4 mm Hg; P less than 0.001), reflecting abnormal internal-anal-sphincter function. The increment in sphincter pressure with voluntary contraction (external-sphincter function) was not significantly different from normal. Incontinent diabetics also had impaired continence for a solid sphere and for rectally infused saline. In contrast, 14 diabetics without diarrhea or incontinence had normal sphincter pressures and normal results on tests of continence, even though 79 per cent had evidence of autonomic neuropathy and nearly half had steatorrhea. We conclude that incontinence in diabetic patients is related to abnormal internal-anal-sphincter function, and that as a group, diabetics without diarrhea do not have latent defects in continence.

Third-degree obstetric perineal tear: long-term clinical and functional results after primary repair

BACKGROUND

This study was designed to investigate the long-term clinical and anorectal functional results after primary repair of a third-degree obstetrical perineal rupture.

METHODS

One hundred and fifty-six consecutive women who had a primary repair of a third-degree perineal rupture were sent a questionnaire and asked to undergo anorectal function testing (anal manometry, anorectal sensitivity, anal endosonography and pudendal nerve terminal motor latency (PNTML)) RESULTS: Some 117 women (75 per cent) responded. Anal incontinence was present in 47 women (40 per cent); however, in most cases only mild symptoms were present. In 40 women additional anorectal function tests were performed and compared with findings in normal controls. Mean(s.d.) maximum squeeze pressure (31(15) versus 63(17) mmHg, P< 0.001) was decreased and first sensation to filling of the rectum (88(47) versus 66(33) ml, P=0.03) and anal mucosal electrosensitivity (4.7(1.7) versus 2.5(0.8) mA, P=0.003) were increased compared with values in normal controls. In 35 women (88 per cent) a sphincter defect was found with anal endosonography. Factors related to anal incontinence were the presence of a combined anal sphincter defect (relative risk (RR) 1.7 (95 per cent confidence interval (c.i.) 1.1-2.8)) or subsequent vaginal delivery (RR 1.6 (95 per cent c.i. 1.1-2.5)).

CONCLUSION

Anal incontinence prevails in 40 per cent of women 5 years after primary repair of a third-degree perineal rupture. The presence of a combined sphincter defect or subsequent vaginal delivery increase the risk of anal incontinence.

Relationship of symptoms in faecal incontinence to specific sphincter abnormalities

We aimed to determine if the type of clinical presentation in patients with faecal incontinence correlated with the underlying sphincter pathology. One hundred fifty one consecutive patients (129 female) with faecal incontinence were classified as having either passive (faecal incontinence without the patient's knowledge) or urge incontinence (incontinence occurring with the patient's awareness, against their will because of lack of voluntary control), and were investigated by routine anorectal physiological testing and anal endosonography. Sixty six patients had passive incontinence (PI) only, 42 patients had urge incontinence (UI) only, 38 patients had combined passive and urge incontinence, and 5 patients had soiling after defaecation only. Patients with PI alone (n = 66) were significantly older than those with UI alone (PI vs UI, 60 vs 42 yr, p < 0.001), had a lower maximum resting anal pressure (51 vs 64 cm H2O, means, p = 0.02) and had a significantly (p < 0.001) greater prevalence of internal anal sphincter (IAS) defects. Patients with UI alone (n = 42) had a significantly lower maximum voluntary contraction pressure (PI v UI, 72 v 42 cm H2O, p < 0.001), and a significantly (p < 0.001) greater prevalence of external anal sphincter (EAS) defects. The clinical classification of faecal incontinence into passive and urge incontinence relates to specific patterns of abnormality of the internal and external anal sphincters.

Nerve mediated relaxation of the human internal anal sphincter: the role of nitric oxide

The aim of this study was to determine if nitric oxide (NO) is the non-adrenergic, non-cholinergic neurotransmitter, released by enteric inhibitory nerves, which mediates relaxation of the human internal anal sphincter. Isolated muscle strips were mounted for isometric tension recording in superfusion organ baths. Sodium nitroprusside, an exogenous donor of NO, relaxed the strips in a concentration dependent manner. In the presence of atropine and guanethidine, transmural field stimulation produced tetrodotoxin sensitive relaxations, which were inhibited in a dose dependent and enantiomer specific manner by antagonists of NO synthase; completely by L-nitroarginine and partially by L-N-monomethyl arginine. The effect of these antagonists was reversed by L-arginine but not D-arginine. Oxyhaemoglobin, a scavenger of nitric oxide, also abolished the relaxations but methaemoglobin had no such effect. These results strongly suggest that NO is, or is very closely associated with, the non-adrenergic, non-cholinergic neurotransmitter mediating neurogenic relaxation of the human internal anal sphincter.

Influence of autonomic nerves on the internal and sphincter in man

The internal and sphincter receives its parasympathetic nerve supply from the sacral outflow and its sympathetic supply from the thoracicolumbar outflow of the spinal cord. In order to investigate the influence of the tonic discharge of these nerves, eight healthy subjects receiving high spinal anaesthesia (T 6-T 12) and five receiving low spinal anaesthesia (L 5-S 1) were examined. Continuous recordings of anal pressure and electromyographic activity from the external sphincter were obtained during rest and during expansion of the ampulla recti by means of an air-filled balloon. The results were compared with those obtained in an earlier study from 10 subjects with a bilateral pudendal block which paralysed the striated sphincter muscles without affecting the autonomic nerve supply to the internal sphincter. Anal pressure at rest decreased significantly more with high spinal anaesthesia (32 +/- 3-2 mm Hg) than with low (11 +/- 7-1 mm Hg) or with pudendal block (10 +/- 3-9 mm Hg) and the relaxations of the internal sphincter induced by rectal distension were somewhat smaller with high spinal anaesthesia. However, the remaining anal pressure at maximal relaxation, induced by a substantial rectal distension, was essentially the same with the three forms of anaesthesia. It is concluded that, at rest, there is a tonic excitatory sympathetic discharge to the internal anal sphincter in man. However, this seems to be without excitatory effect when the sphincter is relaxed after a substantial rectal distension. Furthermore, the results indicate that at rest there is no tonic parasympathetic discharge affecting the sphincter tone.

Receptive fields of unmyelinated ventral root afferent fibres in the cat

1. The receptive fields were determined for 118 afferent fibres in the S2, S3 and Ca (caudal) 1 ventral roots of the cat. Of these fibres, ninety-three were unmyelinated, another eleven were probably unmyelinated, and fourteen were myelinated, according to estimates of their conduction velocities. 2. Confirmation that the recordings were from ventral root filaments came from electron microscopic inspection of ten of the filaments from which recordings of the activity of unmyelinated afferents were made. 3. Receptive fields were demonstrated for twelve unmyelinated afferent fibres in the distal stumps of the S2 and S3 ventral roots which had been sectioned 3 weeks previously, indicating that the cell bodies giving rise to these fibres were not in the spinal cord. 4. The action potentials of some of the unmyelinated ventral root afferent fibres were complex, suggesting branching of the afferents within the ventral root. 5. One third of the unmyelinated ventral root afferents had receptive fields in somatic structures: the skin and deep tissues. 6. Two thirds of the unmyelinated ventral root afferents had receptive fields in the viscera of the pelvis: the bladder, urethra, vagina, and lower bowel. 7. Many of the unmyelinated afferents in the ventral roots, especially those with cutaneous receptive fields, had high thresholds and may participate in nociception. 8. It is concluded that the cat ventral root contains a major sensory component and that the Law of Bell and Magendie is not an accurate description of the organization of the ventral root in this animal.

Normal proximal and delayed distal conduction in the pudendal nerves of patients with idiopathic (neurogenic) faecal incontinence

The latency of the response in the external anal sphincter muscle following transcutaneous stimulation of the cauda equina at the L1 vertebral level was measured in nine women with neurogenic faecal incontinence (mean 7.3 SD 0.7 ms) and 11 normal subjects (mean 5.6 SD 0.6 ms) (p = 0.01). There was no difference in conduction velocity between the L1 and L4 vertebral levels thus supporting the suggestion that conduction delay in faecal incontinence occurs distally.