The effects of simulated hydropower turbine rapid decompression on two Neotropical fish species.

Barotrauma is a major cause of injury and mortality of fish as they pass through hydropower turbines. Current understanding of hydropower related barotrauma is biased towards northern temperate and southern subtropical species with single chambered swim bladders, specifically North American and Australian species, respectively. Today, unprecedented hydropower development is taking place in Neotropical regions where many species have complex multi-chambered swim bladder architecture. This study investigated barotrauma in two dual-chambered physostomous Neotropical fish (pacu, Piaractus mesopotamicus, and piracanjuba, Brycon orbignyanus) exposed to rapid (< 1 s) decompression at different Ratios of Pressure Change (RPC), using a hypo-hyperbaric chamber. The incidence and intensity (percentage surface area of organ affected) of injury and physiological and behavioural response (hereafter just response) of each species immediately after decompression was assessed. Twenty-two injury types (e.g. gill haemorrhage and exophthalmia) and eight response categories (e.g. rising to the surface and loss of orientation) were identified and the influence of: 1) species, 2) RPC, and 3) swim bladder rupture on each was quantified. There was considerable interspecific difference with emboli type injuries occurring more frequently in piracanjuba, but injury intensity tending to be higher in pacu. Both swim bladder chambers tended to rupture in piracanjuba but only the anterior chamber in pacu. RPC was positively correlated with response, incidence and intensity of several injury types for both species with some injuries occurring at very low RPC (e.g. 50 % probability of swim bladder rupture at 2.2 and 1.75 for piracanjuba and pacu, respectively). Multiple responses (e.g. loss of orientation) and injuries (e.g. eye haemorrhage) were correlated with swim bladder rupture suggesting gas venting into the body cavity likely causes secondary injury. When directly comparing our results with those available in the published literature, both pacu and piracanjuba appear to be more susceptible to barotrauma than previously studied subtropical and temperate species.

Applying appropriate frequency criteria to advance acoustic behavioural guidance systems for fish.

Deterrents that use acoustics to guide fish away from dangerous areas depend on the elicitation of avoidance in the target species. Acoustic deterrents select the optimum frequency based on an assumption that highest avoidance is likely to occur at the greatest sensitivity. However, such an assumption may be unfounded. Using goldfish (Carassius auratus) as a suitable experimental model, this study tested this as a null hypothesis. Under laboratory conditions, the deterrence thresholds of individual goldfish exposed to 120 ms tones at six frequencies (250-2000 Hz) and four Sound Pressure Levels (SPL 115-145 dB) were quantified. The deterrence threshold defined as the SPL at which 25% of the tested population startled was calculated and compared to the hearing threshold obtained using Auditory Evoked Potential and particle acceleration threshold data. The optimum frequency to elicit a startle response was 250 Hz; different from the published hearing and particle acceleration sensitivities based on audiograms. The difference between the deterrence threshold and published hearing threshold data varied from 47.1 dB at 250 Hz to 76 dB at 600 Hz. This study demonstrates that information obtained from audiograms may poorly predict the most suitable frequencies at which avoidance behaviours are elicited in fish.

The role of thrombolysis in the management of thromboembolic disorders: a four-year review.

OBJECTIVE: To examine the role of thrombolysis alone, or in conjunction with surgery and angioplasty, in the treatment of thromboembolic disorders. DESIGN: A retrospective review of 70 patients, who received thrombolysis on 73 occasions between 1990 and 1993. PATIENTS AND METHODS: Four groups were defined: (1) thrombolysis alone (40%); (2) thrombolysis followed by angioplasty (23%); (3) thrombolysis followed by surgery (13%) and (4) thrombolysis after failed angioplasty (24%). RESULTS: Twenty-eight patients (40%) received thrombolysis alone of which 13 were successful. In 25 cases (36%) thrombolysis was initially successful in that it permitted further angioplasty or surgical reconstruction. This adjunctive treatment was successful in 16 cases. Overall, when used as a first-line treatment, thrombolysis was successful in 72% of cases. Success in this context includes those in which a further procedure was possible after thrombolysis. These groups included 20 occluded grafts in which thrombolysis played an important part in unblocking 13 (65%) of them. In a separate group of 17 patients (24%) thrombolysis was given after failed angioplasty and was successful on 15 (88%) occasions. Local complications occurred in 17 patients. There were three deaths. There were no intra-cerebral haemorrhages. CONCLUSIONS: Thrombolysis alone can be used successfully. There is a large group in which thrombolysis can help to increase the success rate of interventional radiology.

Simultaneous measurement of gastric emptying, small bowel residence and colonic filling of a solid meal by the use of the gamma camera.

A method for determining the profiles of gastric emptying, small intestinal residence, and colonic filling of a solid test meal, labelled with 250 microCi 99mTechnetium sulphur colloid has been evaluated in nine healthy volunteers and six patients with a disturbance in bowel habit. Mean small bowel transit time was determined by deconvolving the rate of colonic filling with the rate of gastric emptying. In normal subjects, the stomach appeared to empty exponentially with a half time of 1.2 +/- 0.3 hours (mean +/- SD). Food reached the colon by 2.8 +/- 1.5 hours. The mean small bowel transit time was 4.0 +/- 1.4 hours. In most normal subjects, the colon appeared to fill in a linear fashion with approximately 16% food residues entering every hour, and the profile of colonic filling in normal subjects was similar to the profile of ileal emptying observed after feeding a similar radiolabelled solid meal to 14 patients equipped with terminal ileostomies. There was a highly significant correlation between the onset of breath hydrogen excretion and the appearance of radioactivity over the caecum (r = 0.88, p less than 0.01), though in one third of subjects the increase in caecal radioactivity preceded the rise in breath hydrogen concentration by more than 20 minutes. There was also a highly significant correlation between the mean transit time and values for colonic filling but not values for gastric emptying. Patients with irritable bowel syndrome who had diarrhoea tended towards short small bowel transit and early colonic filling, whereas patients who have constipation tended towards long small bowel transit and delayed colonic filling. This method offers a novel means of assessing small bowel transit time, small bowel residence and the profile of colonic filling in man.

Interpretation of the breath hydrogen profile obtained after ingesting a solid meal containing unabsorbable carbohydrate.

The extent to which monitoring breath hydrogen excretion provides information concerning the entry of the residues of a solid test meal into the colon was investigated in 89 normal subjects, and 11 patients with the irritable bowel syndrome. The profile of breath hydrogen concentration showed an early peak, that occurred soon after ingesting the test meal in 89% subjects. This was followed by a later more prolonged rise in breath hydrogen concentration. The early peak occurred well before a radioactive marker, incorporated in the test meal, reached the caecum and the data suggest it was predominantly caused by the emptying of the remnants of the previous meal from the ileum into the colon. This hypothesis was supported by direct measurements of the rate of delivery of ileostomy effluent in 12 subjects with terminal ileostomies. Fermentation of carbohydrate in the mouth may, however, contribute to the initial peak, but this contribution may be avoided by collecting gas samples from the nares. The secondary rise in breath hydrogen excretion was closely correlated with the arrival of the radioactive marker in the caecum (r = 0.91), p less than 0.001), though the time, at which the secondary peak of breath hydrogen excretion occurred was poorly correlated with the time that all the radioactive test meal had entered the colon. When lactulose was infused directly into the colon, as little as 0.5 g produced a discernible hydrogen response, which occurred within two minutes of the infusion. Increasing the rate of colonic infusion of a 50 ml solution of 10% lactulose from 0.02 to 0.15 g/min in five subjects significantly increased the breath hydrogen concentration. At infusion rates below 0.075 g lactulose/minute, the peak breath hydrogen response preceded the end ot the infusion, while at higher rates of infusion, the peak hydrogen response occurred after the end of the infusion. Although these results confirmed that monitoring breath hydrogen concentration usefully signalled the time taken for a meal containing unabsorbed carbohydrate to reach the colon, it did not reliably indicate the time when all of the meal had entered the colon. Finally, the use of the maximum increase in breath hydrogen concentration as an index of the degree of carbohydrate malabsorption assumes uniform rates of entry into the colon.

Effect of ileal infusion of intralipid on gastrointestinal transit, ileal flow rate, and carbohydrate absorption in humans after ingestion of a liquid meal.

The effects of ileal infusion of Intralipid on the time required for a radiolabeled liquid starch meal to empty from the stomach and reach a point in the ileum that was 230 cm from the teeth and on the ileal flow rates and the degree of carbohydrate absorption were measured in 5 normal volunteers. The subjects were intubated with a four-lumen polyvinyl tube. Studies were carried out on consecutive days in random order. Infusion of fat into the ileum (a) slowed the transit of a liquid meal through the stomach, (b) delayed the arrival of the liquid meal in the ileum and increased its residence in the upper small intestine, (c) reduced the average flow of digesta through the upper small intestine and altered the pattern of flow, (d) reduced the volume of the meal entering the ileum, and (e) reduced the degree of carbohydrate absorption in the upper small intestine. These results suggest that the presence of fat in the ileum may have a profound influence on the digestion and absorption of a meal.

Metoclopramide reduces carbohydrate absorption in man.

The effect of metoclopramide (20 mg p.o) on the times taken for a radiolabelled liquid starch meal to empty from the stomach and to reach the ileum (230 cm from the mouth), the ileal flow rates and the degree of carbohydrate absorption were studied in five normal male volunteers, intubated with a four lumen intestinal tube. Administration of metoclopramide significantly reduced the time taken for delivery of 50% and 80% of the meal to the ileal aspiration site, but had no significant effect on the half time for gastric emptying. Administration of metoclopramide did not affect the average flow rate or the total postprandial volume, which passed the ileal aspiration site. Administration of metoclopramide reduced carbohydrate absorption in every subject by between 8 and 30%. This study is consistent with the hypothesis that metoclopramide may reduce the degree of absorption in the human small intestine by decreasing the contact time between food and small intestinal epithelium, though it could also act by reducing the area of mucosa in contact with nutrients.

Does guar gum improve post-prandial hyperglycaemia in humans by reducing small intestinal contact area?

The possibility that viscous polysaccharides, such as guar gum, could lower post-prandial blood glucose levels in part by restricting carbohydrate solutions to a smaller area of small intestine was investigated in twenty healthy human volunteers. Addition of guar gum (22.5 g/l) delayed the mouth-to-caecum transit time of a hypotonic lactulose drink, but did not affect gastric emptying. When a 250 ml solution containing 50 g glucose was confined to a 550 mm length of intestine by an occluding balloon attached to an intestinal tube, maximum blood glucose response was significantly reduced (P less than 0.05) though only by 0.9 mmol/l. Addition of guar gum (36 g/l) had no effect on the distribution of a radio-labelled glucose drink (250 ml; 200 g glucose/l) in the small intestine, monitored using a gamma camera, although it significantly delayed gastric emptying (t 1/2 (min): guar gum v. control 115 (SE 15) v. 73 (SE 8)). Reduced contact area is unlikely to be one of the mechanisms by which guar gum improves glucose tolerance.

The mechanism of action of guar gum in improving glucose tolerance in man.

Experiments were carried out in human volunteers to investigate the mechanism by which guar gum improves glucose tolerance. Guar reduced both plasma glucose and insulin responses to an oral glucose load, and delayed gastric emptying. However, there was no correlation between changes in individual blood glucose responses and changes in gastric emptying rates induced by guar. With a steady-state perfusion technique, glucose absorption was found to be significantly reduced during perfusion of the jejunum with solutions containing guar, but returned to control values during subsequent guar-free perfusions. Preperfusing the intestine with guar did not affect electrical measurements of unstirred layer thickness in the human jejunum in vivo. Experiments in vitro established that glucose diffusion out of a guar/glucose mixture was delayed under conditions of constant stirring. We conclude that guar improves glucose tolerance predominantly by reducing glucose absorption in the small intestine. It probably does this by inhibiting the effects of intestinal motility on fluid convection.

Relationship between small bowel transit time and absorption of a solid meal. Influence of metoclopramide, magnesium sulfate, and lactulose.

The times taken for a radiolabeled solid meal to empty from the stomach and terminal ileum and the absorption of the components of that meal were measured in 14 patients with terminal ileostomies under control conditions and after administration of either lactulose (40 g) or metoclopramide (20 mg tds), or magnesium sulfate (0.1 g/kg body weight). Absorption of each of the components of the meal was determined by chemical analysis of the ileostomy effluent. The radioisotope proved an excellent marker for the delivery of fat, protein, and carbohydrate residues. All three agents significantly reduced the time taken for the meal to empty from the ileum. This was associated with significant reductions in the absorption of fat, carbohydrate, protein, water, and electrolytes in the case of lactulose and magnesium sulfate. Although metoclopramide reduced transit time to the same degree as the other agents, its effect on absorption of fat, fluid, and electrolytes was much less, and absorption of protein and carbohydrate was unaffected. We therefore conclude that, although agents that accelerate postprandial transit of a meal may diminish absorption of the component of that meal in the small bowel, the extent to which this occurs cannot be predicted by a knowledge of transit kinetics alone and depends on the means by which transit is altered. The action of lactulose on the small intestine causes fluid and fat losses, sufficient to result in diarrhea and steatorrhea in a normal subject.

Effect of prolonged exercise on the passage of a solid meal through the stomach and small intestine.

The effect of intermittent moderate exercise on the passage of a solid meal, labelled with radioactive Technetium sulphur colloid, through the stomach and small intestine was investigated by paired studies on seven healthy volunteers. Measurements of gastric radioactivity and breath hydrogen exertion were recorded every 10 minutes while subjects exercised in a controlled manner while seated on a bicycle ergometer. These were compared with values obtained during a separate experiment while the same subjects sat upright in a chair. Exercise significantly accelerated gastric emptying (control t 1/2 = 1.5 +/- 0.1 h; exercise t 1/2 = 1.2 +/- 0.1 h; p less than 0.02) but had no significant effect on small bowel transit time.

Is the transit time of a meal through the small intestine related to the rate at which it leaves the stomach?

Using non-invasive techniques, we investigated how varying the size or composition of a meal altered the rate at which it passed through the stomach and small intestine in normal volunteers. Increasing the size of the meal by doubling the absorbable components delayed gastric emptying, did not significantly influence the time taken for the head of the meal to reach the caecum, but retarded the entry of the bulk of the meal residues into the caecum. Incorporating fat in the meal slowed gastric emptying, but did not significantly affect small bowel transit time. The addition of the unabsorbable disaccharide lactulose (in place of an equivalent amount of sucrose) accelerated small bowel transit time, but did not significantly influence gastric emptying. Thus, our results indicated that changes in small bowel transit time could occur independently of changes in gastric emptying in normal healthy subjects.

Transit of a meal through the stomach, small intestine, and colon in normal subjects and its role in the pathogenesis of diarrhea.

A method for measuring the transit time of a meal, containing sausages, mashed potato, baked beans, and a pineapple custard dessert, through the gastrointestinal tract was evaluated in 14 healthy volunteers. Gastric emptying was determined by incorporating a radioactive marker in the meal and counting over the surface of the stomach using a crystal scintillation detector. Small intestinal transit time was determined by measuring breath hydrogen excretion and by estimating the radioactivity over the cecum. Finally, whole gut transit time was measured by incorporating radiopaque plastic markers or carmine red in the meal and estimating the appearance of these markers in the stool. Our results showed that measurements of small intestinal transit time were reproducible and in the majority of subjects the increase in hydrogen excretion occurred at the same time as the increase in radioactive counts over the surface of the cecum. The passage of the first marker in the stool coincided with the appearance of carmine red. There were no significant correlations between small intestinal transit time and whole gut transit time or the half time for gastric emptying. Incorporation of 10, 25, and 40 g lactulose into our standard meal in place of sucrose increased the rate of transit through the small intestine but did not significantly alter the rate of gastric emptying or the whole gut transit time. Total stool weight for 48 hr after ingestion of the meal was inversely related to whole gut transit time but not to small intestinal transit time suggesting that the tendency to develop diarrhea in response to a meal containing unabsorbable carbohydrate depends more on the lack of colonic accommodation than on the rate of small intestinal transit. Finally, there was no significant correlation between the measurements of small intestinal transit time after a drink of lactulose and the transit time of a meal in the same subjects.