Widespread omnivory and low temporal and spatial variation in the diet of fishes in a hydrologically variable northern Australian river.

This article examines the trophic ecology of freshwater fishes (22 species in 15 families) in a wet and dry tropical Australian river of high intra-annual and interannual hydrological variability. Seven major trophic groups were identified by cluster analysis; however, four food items (filamentous algae, chironomid larvae, Trichoptera larvae and Ephemeroptera nymphs) comprised almost half of the average diet of all species. The influence of species, fish size, spatial effects and temporal effects on food use was investigated using redundancy analysis. Size, time and space accounted for little of the perceived variation. Ontogenetic changes in diet were minor and limited to a few large species. Spatial variation in trophic composition of the fish assemblages reflected the effects of the Burdekin Falls and dam, a major geographic barrier, on species distributions. Little spatial variation in diet was detected after accounting for this biogeographical effect. Temporal variations in flow, although marked, had little effect on variations in fish diet composition due to the low temporal diversity of food resources in physically monotonous sand and gravel channels. Species identity accounted for<50% of the observed variation in food choice; omnivory and generalism were pronounced. The aquatic food web of the Burdekin River appears simple, supported largely by autochthonous production (filamentous and benthic microalgae, and to some extent, aquatic macrophytes). Allochthonous food resources appear to be unimportant. The generalist feeding strategies, widespread omnivory and absence of pronounced trophic segregation reported here for Burdekin River fishes may be common to variable and intermittent rivers of subtropical and tropical northern Australia with similar fish communities and may be a general feature of rivers of low habitat diversity and characterized by flow regimes that vary greatly both within and between years.

Role of anorectal sensation in preserving continence.

The role of anal sensation in preserving continence was studied in nine healthy volunteers. Objective assessment of sphincter function by manometry and rectal saline infusion was carried out during topical anaesthesia of the anal canal using 5% lignocaine gel and during lubrication with the same amount of inert gel. Anaesthesia successfully abolished anal sensation and reduced both the amplitude and duration of the voluntary squeeze. Basal pressure was unaffected, but the rectal volume required to produce a sustained internal sphincter relaxation was increased. Saline continence was not impaired. Indeed, two subjects, who were previously unable to retain the full 1500 ml of rectally infused saline, did so when the anal canal was anaesthetised. Our findings suggest that anal sensation is not a critical factor in preserving continence. This implies that the incontinence experienced after anorectal surgery or neuropathy cannot be explained by lack of anal sensation alone.

Differences in anal function in patients with incontinence to solids and in patients with incontinence to liquids.

Manometric radiological and neurophysiological measurements of the anal sphincter were carried out in 19 female patients who were incontinent to liquid faeces only, 15 female patients who exhibited incontinence to solid and liquid faeces and 18 normal female controls. Both groups of patients had abnormally obtuse anorectal angulation and perineal descent, a weak and easily inhibited sphincter tone and similar degrees of neuropathy during electromyography. However, patients who were incontinent to solids and liquids exhibited lower squeeze pressures during standard manometry and lower peak pressures during saline infusion than patients who were only incontinent to liquids. These findings suggest that it is the additional weakness of the external sphincter that renders patients incontinent to solids as well as liquids.

Differences in anorectal manometry between patients with haemorrhoids and patients with descending perineum syndrome: implications for management.

Anorectal manometry was carried out at rest, during balloon distension of the rectum and during rectal infusion of saline in 19 patients with haemorrhoids, 30 patients with descending perineum syndrome and 21 controls. Basal and squeeze pressures were significantly higher in patients with haemorrhoids than patients with the descending perineum syndrome. A lower rectal volume was required to inhibit internal sphincter tone in patients with descending perineum syndrome compared with control subjects or patients with haemorrhoids. During rectal infusion of saline basal and peak anal pressures in patients with the descending perineum syndrome were lower than in haemorrhoid patients. Peak rectal pressure was abnormally high in both groups. These differences in anorectal function suggest that despite a similar presentation, the two conditions have a different pathogenesis. Moreover, inappropriate anal sphincter stretch or mucosal excision in patients with descending perineum syndrome may lead to severe incontinence.

The role of partial denervation of the puborectalis in idiopathic faecal incontinence.

Recent studies have suggested that patients with idiopathic faecal incontinence have neuropathic damage to the external and sphincter and pelvic floor musculature, though no direct assessment of puborectalis function has been made in intact man. Obstetric trauma and chronic straining at stool are thought to be possible causes for damage to the puborectalis nerve supply. In this study the motor unit potential duration in the external sphincter and puborectalis was measured by conventional electromyography in incontinent patients and two groups of continent patients who strained at stool. Our results confirm that incontinent patients had significant neuropathic damage to the puborectalis and the external sphincter compared with controls. Patients with the descending perineum syndrome, who were continent, showed partial denervation of the external sphincter and puborectalis, though the degree of abnormality in puborectalis was less than that in incontinent patients. Finally, patients with constipation showed neurogenic abnormalities in the external anal sphincter but not in the puborectalis. The findings suggest that partial denervation of the external sphincter can occur independently of partial denervation of the puborectalis in patients who strain at stool but if severe changes are present in both muscles, the patient is likely to be incontinent.

Differences in anal sphincter function and clinical presentation in patients with pelvic floor descent.

Perineal descent is found in patients with idiopathic fecal incontinence and patients with the descending perineum syndrome, who have little or no incontinence but present with a symptom pattern that suggests obstructed defecation. To investigate why patients with perineal descent present in different ways, manometric, radiologic, and neurophysiologic studies were performed in 53 patients with radiologically proven perineal descent and 34 control subjects. Thirty-two patients exhibited incontinence to rectally infused saline, while 21 patients presented with obstructed defecation but exhibited no incontinence. Both patient groups exhibited similar degrees of perineal descent on straining and increases in the motor unit potential duration of the external anal sphincter, indicative of neuropathic damage. Both groups had an abnormal rectoanal inhibitory reflex and an abnormal anorectal angle, though the latter was more obtuse in idiopathic fecal incontinence. However, although patients with incontinence had lower maximum basal and maximum squeeze sphincter pressures than normal, these values were normal in patients with obstructed defecation. Our findings suggest that perineal descent and neuropathy are not necessarily associated with incontinence as long as sphincter pressures remain normal.

A prospective study of the effect of haemorrhoidectomy on sphincter function and faecal continence.

The effect of haemorrhoidectomy on anal sphincter manometry and continence to faeces and rectally infused saline was investigated in 24 unselected patients with third-degree haemorrhoids. Haemorrhoidectomy resulted in the abolition of ultra-slow waves and significant decreases in basal and squeeze pressures, though these were reduced to normal values from abnormally high levels. Pressures remained at normal levels up to a year after surgery. An association was found between mucous soiling following surgery and an abnormally low postoperative squeeze pressure. There was no alteration in the function of the recto-anal inhibitory reflex following surgery. Only two patients developed incontinence to rectally infused saline for the first time following surgery. The addition of four-finger dilatation of the anal canal to the operative procedure did not cause any significant differences in sphincter manometry.

A report of five patients with large-volume secretory diarrhea but no evidence of endocrine tumor or laxative abuse.

The purpose of this paper is to report five patients with chronic secretory diarrhea (maximum stool volume greater than 1 liter per day, duration 6 weeks to 8 years) in whom we could find no evidence of an endocrine tumor or of surreptitious laxative ingestion. All except one had severe hypokalemia. There was apparent improvement after treatment with prednisone in two patients and loperamide in one. The diarrhea resolved spontaneously in three patients and has undergone several temporary remissions in one patient. The last patient died after a severe unremitting illness. Extensive investigations failed to establish the etiology, but intestinal perfusion (carried out in four of the five patients) revealed secretion or abnormally low absorption of water and electrolytes in the jejunum and abnormally low absorption in the colon. The management of patients with chronic watery diarrhea is discussed.

Anorectal function in elderly patients with fecal impaction.

Manometric and other investigations were carried out in 55 elderly patients who had impacted masses of feces in the rectum upon admission to hospital and in 36 elderly age- and sex-matched control subjects. Maximum basal and maximum squeeze sphincter pressures in the patients were similar to those in the elderly controls. Most elderly patients in the impacted group and all control subjects were able to pass a 50-ml balloon from the rectum, although a lower proportion of patients, admitted with impaction, could expel a small solid sphere. In patients the rectum had to be distended with larger volumes than in controls before the presence of the rectal balloon, pain, and the desire to defecate were perceived and before rectal contractions were generated. Rectal pressures, recorded during rectal distention, were lower in the impacted group than in the control group. Finally, anal and perianal sensation was impaired in patients with fecal impaction. These findings are similar to those described in patients with low spinal cord injuries.

Use of anorectal manometry during rectal infusion of saline to investigate sphincter function in incontinent patients.

Anal and rectal pressures and external sphincter electromyogram were recorded continuously during rectal infusion of 1.5 L saline in 18 normal subjects and 37 patients who complained of diarrhea and fecal incontinence. All subjects exhibited a pattern of regular fluctuations in anorectal pressure and electromyogram. All except 1 of the normal subjects were able to retain 1500 ml saline without leakage, and their pressure record comprised simultaneous rectal contractions, internal sphincter relaxations, and external sphincter contractions. None of the incontinent patients were able to retain 1500 ml saline without leakages, and leakages always coincided with the peaks of rectal pressure. Two manometric patterns were observed. Fifty-nine percent of incontinent patients exhibited a pattern of contractions of similar profile occurring throughout the anorectum. This finding was associated with low basal sphincter pressures, an easily inhibited anal sphincter tone, an obtuse anorectal angle, and a funnel-shaped configuration to the anal canal. These results suggested that, in this group, the internal sphincter was weak and easily inhibited so that the whole anorectum behaved as one fluid-filled compartment recording contractions of the external sphincter. The remaining 41% of incontinent patients exhibited a normal pattern of anorectal pressure fluctuations and had normal maximum basal pressures, although maximum squeeze pressures, rectoanal inhibitory reflex, and anorectal angles were abnormal. Peak rectal pressures were abnormally high in this group during saline infusion, suggesting that abnormally strong rectal contractions may play a role in the incontinence in this group.

Chronic diarrhea of unknown origin.

We studied 27 patients with severe chronic diarrhea for which extensive investigations carried out at other institutions had failed to reveal a diagnosis. They were studied by standard diagnostic methods as well as by careful fecal analysis and intestinal perfusion. If they were incontinent of feces, anal sphincter function tests were performed. Although many were suspected of having pancreatic cholera syndrome, this diagnosis could not be established in a single patient. The most common diagnosis that could be established was surreptitious ingestion of drugs (laxatives in 7 patients and diuretics in 2). Other specific diagnoses included ulcerative colitis in 2 patients, allergy to beef in 1, and bacterial overgrowth of the small intestine in 1. Thus, we were able to establish a specific diagnosis in 13 patients. Of the remaining 14 patients, 8 had findings suggestive of irritable bowel syndrome, and 2 others had anal sphincter dysfunction as the major cause of their disability. The other 4 undiagnosed patients had severe secretory (3 patients) or osmotic (1 patient) diarrhea. Follow-up interviews at 6 mo-6 yr failed to reveal evidence of a cause for diarrhea that had been overlooked during our studies. The diagnostic approach to patients with unexplained diarrhea is discussed. The importance of a search for surreptitious drug ingestion and accurate measurement of bowel movement frequency and stool weight is emphasized.