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Biomedical subjects

J Dent

Publications and source records attributed to J Dent.

At least 145 records · Page 8Linked to original sources
PubMed1995

Effects of posture on gastric emptying of nonnutrient liquids and antropyloroduodenal motility.

The effects of posture on gastric emptying, intragastric distribution, and antropyloroduodenal motility after ingestion of a nonnutrient liquid have been evaluated. In seven healthy volunteers antropyloroduodenal pressures were measured for 30 min after ingestion of 150 ml of normal saline in two different positions: sitting and left lateral. Saline drinks were radiolabeled and ingested both before and after intravenous atropine (4 micrograms/kg). Rates of emptying from both the total (P < 0.05) and the proximal (P < 0.05) stomach were faster in the sitting position than in the left lateral position. There were more long (> 6 cm) antropyloric pressure waves (P < 0.05) and isolated pyloric pressure waves (P < 0.05) in the sitting position. Intravenous atropine slowed emptying in both positions (P < 0.05) and in the sitting position decreased (P < 0.05) the number of antropyloric pressure waves. After atropine, gastric emptying was also faster in the sitting compared with the decubitus position (P < 0.05), although there was no difference in antropyloric or isolated pyloric pressure waves between the two postures. We conclude that the effects of gravity on gastric emptying of nonnutrient liquids are likely to reflect changes in both antropyloric motility and intragastric distribution.

Adolescent↗
PubMed1995

Responses of ferret lower esophageal sphincter to 5-hydroxytryptamine: pathways and receptor subtypes.

In urethananesthetized ferrets, basal lower esophageal sphincter pressure (LESP) was unaffected by the 5-hydroxytryptamine3 (5-HT3) receptor antagonist granisetron (0.5 mg/kg) or by greater splanchnic nerve section (GSX), but increased after bilateral vagotomy. Peripheral vagal nerve stimulation caused LES relaxation, often followed by a brief contraction and a prolonged inhibition of LESP. Close intra-arterial injection of 5-HT (5-100 micrograms) had a biphasic effect on LESP, with a brief drop followed by a prolonged increase. Granisetron (0.5 mg/kg i.v.) abolished the initial relaxation and revealed an earlier peak of excitation. This was not influenced by subsequent vagotomy and GSX. In a series of eight additional experiments (series 2), granisetron was given after vagotomy and GSX. In series 2, 5-HT-induced relaxation was unaffected by vagotomy but was significantly reduced after GSX and was further reduced after granisetron, indicating that 5-HT3 receptor mechanisms may lie on a sympathetic neural pathway. Vagotomy had no effect on the excitatory component. GSX had no effect on the amplitude of excitation, but reduced its latency. Granisetron had no further effect on excitation in series 2. In a separate series of 13 experiments (series 3), the excitatory component of the LES response to 5-HT was abolished by ketanserin (2.5 mg/kg i.v.) , after which only relaxation occurred. Both 5-HT2 and 5-HT3 antagonists in combination abolished all effects of 5-HT on LESP. Atropine (400 micrograms/kg i.v., n = 7) had no effect on 5-HT-induced LES responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Influence of gravity and body position on normal oropharyngeal swallowing.

The influence of gravity, if any, on pharyngeal bolus transport is unknown. The aim of the present study was to evaluate the effect of gravity and body position on the radiological and manometric events during the normal oropharyngeal swallow. In eight healthy male volunteers, we performed simultaneous videoradiography and manometry, using a manometry catheter incorporating a perfused sleeve measuring upper esophageal sphincter pressure and three solid-state transducers recording pharyngeal pressures. Swallows of 5 and 10 ml of barium were performed in three different body positions: upright, horizontal, and 30 degrees head down (inverted). Hypopharyngeal intrabolus pressure increased significantly in the horizontal and inverted positions compared with upright, P = 0.0001. This resulted in increased maximal sphincter diameters during bolus flow (P = 0.0001) and shorter duration of sphincter opening (P = 0.03). As a result, transsphincteric flow increased in the horizontal and inverted positions, P = 0.04. Total swallowing duration, oral and pharyngeal transit time, pharyngeal peristaltic amplitude and duration, the length of the bolus in the pharynx, and excursions of the hyoid and larynx were unaffected by body position. We conclude that intrabolus pressure is an important determinant of upper esophageal sphincter opening in the healthy oropharynx and that gravity does not influence pharyngeal bolus transport. The healthy upper esophageal sphincter has residual opening capacity that can be demonstrated by altering body posture.

Adult↗
PubMed1994

Pyloric motility and liquid gastric emptying during barostatic control of gastric pressure in pigs.

1. In conscious pigs, intragastric pressure was controlled by a water barostat such that the gastroduodenal pressure gradient was always positive with the barostat set above 15 cm. In six pigs pyloric motor function was removed by prior pylorectomy. 2. In pylorus-intact animals, isolated pyloric pressure waves (IPPWs) occurred at a median of 2.9 min-1 during duodenal dextrose infusion with the barostat set at or above a threshold of 15 cm. Increases of intragastric pressure above this threshold had no additional effect upon rates of IPPWs. Below this threshold, with identical duodenal dextrose infusion, IPPWs occurred infrequently (0.5 min-1). In pylorus-excised animals virtually no IPPWs were seen. 3. In both pylorus-intact and -excised animals, the rate of antral pressure waves (APWs) was dependent upon intragastric pressure during duodenal infusion of both saline and dextrose. No threshold for stimulation was seen. Duodenal dextrose infusion inhibited APWs in pylorus-intact animals only. 4. With a positive gastroduodenal pressure gradient, gastric emptying was more rapid in pylorus-excised animals than pylorus-intact animals during duodenal dextrose infusion. In contrast, gastric emptying rates were not different between pylorus-intact and -excised animals during saline infusion. 5. These findings suggest an all-or-none-type stimulation of localized pyloric contractions by distension of the stomach beyond a threshold, in synergism with stimulation by nutrients within the upper small bowel. In contrast, stimulation of antral motility is in proportion to distension of the stomach. The pylorus, by way of localized pyloric contractions, is an effective resistor to transpyloric flow in the face of a positive gastroduodenal pressure gradient.

Animals↗
PubMed1994

Effect of intraoperative manipulation and anaesthesia on lower oesophageal sphincter function during fundoplication.

The variables influencing the intraoperative measurement of lower oesophageal sphincter (LOS) pressure and a new method of assessing the effect of a fundal wrap on LOS function were investigated in 13 patients undergoing fundoplication. All patients had a 360 degrees wrap fashioned around a 50-Fr bougie; four also underwent highly selective vagotomy. The effect of the fundal wrap, independent of LOS pressure, was assessed by inducing LOS relaxation with balloon distension. Preoperative mean(s.e.m.) LOS pressure (14.1(2.6) mmHg) did not correlate with that at the start of operation (11.5(1.5) mmHg). After mobilization of the oesophagus mean(s.e.m.) LOS pressure increased significantly (to 19.8(2.0) mmHg; P < 0.0005) and oesophageal distension elicited LOS relaxation on 16 of 33 occasions. After completion of the wrap there was no further increase in LOS pressure, but LOS relaxation occurred after only five of 33 distensions (P < 0.01). These findings indicate that anaesthesia and intraoperative manipulation during fundoplication have significant effects on LOS function that detract from the validity of intraoperative assessment. They question the rationale of current approaches to intraoperative manometry for the assessment of antireflux surgery.

Adult↗
PubMed1994

Pyloric motility. Sleeve sensor versus strain gauge transducer.

Intraduodenal infusion of nutrients has been shown by intraluminal sleeve-sidehole manometry to suppress antral contractions and stimulate isolated pyloric pressure waves (IPPWs) in humans. It is still unresolved, whether these pyloric contractions occur within an otherwise quiescent zone of motor and electrical activity and whether the presence of the sleeve sensor itself affects this nutrient-associated response. In four conscious dogs, comparisons were made between paired recordings of myoelectrical and motor activities of the antropyloroduodenal region with serosal strain gauge transducers and extracellular bipolar electrodes in the presence and absence of an intraluminal manometric sleeve-sidehole assembly during intraduodenal infusions of saline and a triglyceride emulsion (Intralipid 10%, 0.5 kcal/min). Of 287 isolated pyloric pressure waves, detected by the manometric sleeve sensor, 75% were detected as isolated pyloric contractions by the strain gauge transducers and 72% occurred in the absence of electrical spike activity in the distal antrum or proximal duodenum. The lower incidence of isolated pyloric contractions (strain gauges) was related to: (1) insensitivity of the pyloric strain gauge transducer in comparison to the manometric sleeve sensor (10%), and (2) inability of the manometric sleeve-sidehole assembly to detect pressure waves in the distal antrum (7%) or proximal duodenum (8%) during antral or duodenal wall motion. The presence of the sleeve sensor itself did not affect the number of lipid-induced isolated pyloric contractions but increased their amplitude [median 9 (7-15) mN vs 4 (2-6) mN; P < 0.05].(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Modulation of pumping function of gastric body and antropyloric contractions.

Gastric and antropyloric phasic contractions control transpyloric pulsatile flow, the major mechanism of gastric emptying. Both the occurrence and patterning of phasic gastric contractions are highly modulated by intestinal feedback mechanisms, with resultant variation in gastric emptying. The observed patterns of these contractions can only be plausibly explained by the action of neural influences on gastric motility. These influences derive from several mechanisms driven by intestinal feedback, central nervous system controls, and higher centers, with transmission of signals via intrinsic enteric pathways and extrinsic nerves. It is suggested that the occurrence and patterning of gastric phasic contractions depend on the spatial specificity and local modulation of the intensity of neural stimulation of gastric muscle. The resultant strength of contraction determines the occurrence and timing of lumen occlusion relative to adjacent regions. The timing of lumen occlusion in adjacent regions may be the major determinant of mechanical outcome.

Animals↗
PubMed1994

Effects of duodenal distention on fasting and postprandial antropyloroduodenal motility in humans.

BACKGROUND/AIMS: Mechanoreceptors in the proximal small intestine may play an important role in the regulation of gastric emptying. Balloon distention of the duodenum causes fundic relaxation. The purpose of the present study was to determine the effect of stimulation of duodenal mechanoreceptors on both fasting and postprandial antropyloroduodenal motility in humans. METHODS: Antropyloroduodenal pressures were recorded in 12 healthy volunteers with a sleeve-sidehole assembly, incorporating two balloons 5 and 20 cm distal to the pylorus. Duplicate proximal and distal duodenal balloon distensions with 10, 20, and 30 mL of air for 2.5 minutes were performed separately and in randomized order both during fasting and after a meal. RESULTS: During fasting, proximal and distal distention at all volumes increased the number of isolated pyloric pressure waves (P < 0.05) and basal pyloric pressure (P < 0.05), and the response to proximal distention was greater (P < 0.05). Postprandially, proximal and distal distention increased basal pyloric pressure (P < 0.05) with a greater response to proximal distention (P < 0.05), but had no effect on isolated pyloric pressure waves. Both during fasting and postprandially, there were more synchronous and less antegrade antral waves during distention (P < 0.05). The number of duodenal pressure waves increased during proximal (P < 0.05) but not distal distention. CONCLUSIONS: Stimulation of duodenal mechanoreceptors by balloon distention has significant and region-dependent effects on antropyloroduodenal motility that vary between fasting and postprandial states.

Adult↗
PubMed1994

Transmitter mechanisms in vagal afferent-induced reduction of lower oesophageal sphincter (LOS) pressure in the rat.

The extrinsic neural pathways and transmitter mechanisms involved in neural influences controlling lower oesophageal sphincter (LOS) pressure have been evaluated in three groups of experiments in urethane anaesthetized rats. A miniature perfused sleeve/sidehole catheter measured gastric, LOS and oesophageal pressures. Group 1: Vago-vagal and vago-spinal reflex pathways were activated simultaneously via the central nervous system by stimulation of the central cut end of the left vagus. This caused a prolonged drop in LOS pressure with a rapid onset and a slow return to baseline. Subsequent right (bilateral) vagotomy in these animals increased basal LOSP (P < 0.001). Central vagal stimulation-induced reduction of LOSP was not significantly changed in amplitude but was shorter in duration (P < 0.01) than before bilateral vagotomy. IV administration of the 5-HT3 receptor antagonist granisetron (50 micrograms/kg), after bilateral vagotomy had no effect on the response to central vagal stimulation. The nitric oxide (NO) synthase inhibitor L-nitroarginine methyl ester (L-NAME) (100 mg/kg) reduced the depth of relaxation (P < 0.01) and temporarily increased basal LOSP. Propranolol (1.5 mg/kg, i.v.) subsequently increased basal LOSP (P < 0.01), but had no further effect on the vagal stimulation-induced reduction in LOSP. Alpha adrenergic blockade with phentolamine (1 mg/kg, i.v.) decreased basal LOSP (P < 0.01), and nearly abolished the response to vagal stimulation (P < 0.01). Group 2: Both alpha 1- and alpha 2-adrenoceptors were shown to be involved by the combined use of the more selective antagonists yohimbine (1 mg/kg, i.v.) and prazosin (200 micrograms/kg) in place of phentolamine. Group 3: To observe neurotransmitter mechanisms in the vago-vagal pathway, central left vagal stimulation was performed after left vagotomy, and subsequently after blockade of sympathetic motor pathways with guanethidine (5 mg/kg), leaving intact efferent pathways in the right vagus. Guanethidine increased basal LOSP (P < 0.01), and reduced the duration of vagal-induced LOS relaxation (P < 0.05). Depth of relaxation was unchanged. Subsequently, granisetron and L-NAME had no significant effects. Finally, additional right vagotomy abolished the remaining response. Our data indicate the existence of vago-spinal and vago-vagal inhibitory reflex pathways to the rat LOS. The inhibitory vago-spinal pathway is mainly alpha-adrenergic, and has a minor NO-mediated component, but no 5-HT3 receptor-mediated mechanism. In the vago-vagal pathway, no significant involvement of NO-mediated or 5-HT3 receptor-mediated effects was observed. Other non-adrenergic inhibitory mechanisms were, however, apparent.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1994

Preservation of gastric antral mucus is associated with failure of eradication of Helicobacter pylori by bismuth, metronidazole and tetracycline.

METHODS: Forty-three patients positive for Helicobacter pylori by histology and culture of antral biopsies (n = 40) or histology alone (n = 3) were investigated. They received either regimen 1--tripotassium dicitrato bismuthate 120 mg q.d.s. and tetracycline 250 mg q.d.s. for 4 weeks, with metronidazole 200 mg q.d.s. for the first 2 weeks, or regimen 2--omeprazole 20 mg b.d., amoxycillin 500 mg t.d.s., tetracycline 500 mg q.d.s. each for 3 weeks. Gastric antral biopsies were scored (0-3) histologically for mucus depletion, polymorphonuclear and mononuclear cell infiltrate. H. pylori eradication was assessed by biopsy and culture 1 month after the cessation of treatment. RESULTS: With regimen 1, pre-treatment mucus depletion was significantly higher where eradication was successful (median score 2) compared to where it was not (median score 1, P < 0.01); there were no differences in the scores for polymorphonuclear or mononuclear cell infiltrates. In patients receiving regimen 2, there were no differences in either mucus depletion or polymorphonuclear or mononuclear cell infiltrate, between those where eradication was successful and those where it was not. Metronidazole minimum inhibitory concentrations rose when eradication with regimen 1 was unsuccessful (median before 0.19 mg/L, median after treatment 16 mg/L; P = 0.04). CONCLUSION: Pre-treatment mucus depletion is identified as a factor affecting H. pylori eradication. Preservation of mucus may facilitate acquisition of metronidazole resistance.

Adult↗
PubMed1994

Strain induced augmentation of upper oesophageal sphincter pressure in children.

The hypothesis that troublesome oesophagopharyngeal reflux arises from defective upper oesophageal sphincter response to straining has been evaluated in 53 children aged two to 81 months (median 13) referred with symptoms thought to be related to gastro-oesophageal reflux. Spontaneously occurring pharyngeal, upper oesophageal sphincter, oesophageal body, and gastric pressures were analysed after feeding. Inspiratory strain was the most common spontaneously occurring strain (172 episodes), defined as an oesophageal body inspiratory negative pressure dip at least twice the size of the normal inspiratory wave. Overall, during inspiratory strain, upper oesophageal sphincter pressure was significantly higher than before straining (p < 0.01) (5 v 27 mm Hg, p < 0.01). Sustained strains defined as increases in gastric and oesophageal body pressure for two to 20 seconds were also common (149 episodes) and when compared with just before straining, also augmented upper oesophageal sphincter pressure (60 v 39 mm Hg, p < 0.01). The vigour of straining, estimated as increase of gastric pressure, correlated significantly with the degree of augmentation of upper oesophageal sphincter pressure (p < 0.05). Children with and without evidence of troublesome oesophagopharyngeal reflux showed no difference in upper oesophageal sphincter response patterns to straining. Failure of augmentation of upper oesophageal sphincter tone in the face of strain induced increases of oesophageal body pressure is probably a secondary factor in the production of oesophagopharyngeal reflux in children.

Child↗
PubMed1994

Postprandial antropyloroduodenal motility and gastric emptying in gastroparesis--effects of cisapride.

There is little information about the organisation of antroduodenal contractions or pyloric motility in patients with gastroparesis. The mechanisms responsible for the acceleration of gastric emptying by cisapride in patients with gastroparesis are also poorly understood. Simultaneous manometric and scintigraphic recordings were performed in 12 patients with gastroparesis and nine healthy volunteers before and after cisapride administration. Antropyloroduodenal pressures were recorded with a sleeve/side hole manometric assembly and gastric emptying with a scintigraphic method. Thirty minutes after the solid component of the test meal had begun to empty from the stomach all subjects received 5 mg cisapride intravenously over 10 minutes and recordings continued for a further 60 minutes. In the 30 minutes before cisapride there was no significant difference in the number of antral pressure waves (median 20 v 33, NS), basal pyloric pressure, or the number of isolated pyloric pressure waves between patients and volunteers, but the number of antral waves of extent > or = 6 cm (median 1 v 5, p < 0.05) was less in the patients, as was gastric emptying (8% v 20%, p < 0.05). In the patients, there was no change in the number of antral waves after cisapride, but there was an increase in the number of antral waves > or = 6 cm in extent (median 7 v 1, p < 0.05) and in the rate of gastric emptying (26% v 8%, p < 0.01). In the healthy subjects, cisapride increased gastric emptying (31% v 20%, p < 0.05), but reduced the number of antral waves (10 v 33, p < 0.05). Cisapride had no significant effect on the number of antral waves of extent more than or equal to 6 cm (11 v 5, NS). The number of isolated pyloric pressure waves decreased after cisapride (4 v 11, p < 0.05). There was a relationship between gastric emptying and the number of antral pressure waves of extent more than or equal to 6 cm in both the patients (r=0.38, p<0.05) and healthy subjects (r=0.05, p<0.01). There was no significant relationship between gastric emptying and the number of antral waves. It is concluded that disturbance of the relationship between antral, pyloric, and duodenal pressure waves is a major abnormality of postprandial gastric motor function in patients with gastroparesis. The stimulation of antral pressure waves of extent more than or equal to 6 cm may contribute to the acceleration of gastric emptying produced by cisapride in patients with gastroparesis and in normal subjects.

Adult↗
PubMed1994

Omeprazole v ranitidine for prevention of relapse in reflux oesophagitis. A controlled double blind trial of their efficacy and safety.

The aim of this study was to compare recurrence rates of reflux oesophagitis (after endoscopic healing with omeprazole) over a 12 month period of randomised, double blind, maintenance treatment with either daily omeprazole (20 mg every morning; n = 53), weekend omeprazole (20 mg on three consecutive days a week, n = 55) or daily ranitidine (150 mg twice daily, n = 51). Patients were assessed for relapse by endoscopy (with gastric biopsy) at six and 12 months, or in the event of symptomatic recurrence, and serum gastrin was monitored. At 12 months, the estimated proportions of patients in remission (actuarial life table method) were 89% when receiving daily omeprazole compared with 32% when receiving weekend omeprazole (difference 57%, p < 0.001, 95% confidence intervals: 42% to 71%) and 25% when receiving daily ranitidine (difference 64%, p < 0.001, 95% confidence intervals: 50% to 78%). Median gastrin concentrations increased slightly during the healing phase, but remained within the normal range and did not change during maintenance treatment. No significant pathological findings were noted, and no adverse events were attributable to the study treatments. In conclusion, for patients who respond favourably to acute treatment with omeprazole 20 mg every morning, the drug is a safe and highly effective maintenance treatment for preventing relapse of reflux oesophagitis and its associated symptoms over 12 months. By contrast, weekend omeprazole and daily ranitidine were ineffective.

Adolescent↗
PubMed1994

Stereospecific effects of intraduodenal tryptophan on pyloric and duodenal motility in humans.

BACKGROUND: L-Tryptophan delays gastric emptying in animals to a greater extent than D-tryptophan, but none of the possible motor mechanisms responsible for this stereospecific effect have been evaluated. METHODS: In 11 healthy volunteers antropyloroduodenal pressures were recorded in the fasted state with a sleeve/sidehole manometric assembly during 20-min intraduodenal infusions (2 ml.min-1) of isotonic L- and D-tryptophan (50 mM, pH 5.7) and normal saline (pH 5.5), given in randomized order. RESULTS: Intraduodenal L-tryptophan increased basal pyloric pressure (p < 0.05), whereas D-tryptophan had no effect. In contrast, L- and D-tryptophan both stimulated (p < 0.05) localized phasic pyloric pressure waves, and there was no significant difference in the responses. The number of duodenal pressure waves was greater during infusion of L-tryptophan than during D-tryptophan (p < 0.05). CONCLUSION: We conclude that intraduodenal tryptophan has stereospecific effects on pyloric and duodenal motility. Although the precise contribution of these differential effects to gastric emptying remains to be clarified, they may be partially responsible for the differences in gastric emptying of D-tryptophan and L-tryptophan.

Adult↗
PubMed1994

Roles of gastric acid and pH in the pathogenesis of gastro-oesophageal reflux disease.

In recent years, gastric acid has been shown to play a major role in the pathogenesis of reflux oesophagitis, though it remains possible that defective oesophageal mucosal resistance may also play some part. Abnormally prolonged and/or frequent exposure of the distal oesophagus to a pH of less than 4 is the major defect; this results from frequent gastro-oesophageal reflux, the impact of which is magnified in about half of the patients by slow oesophageal acid clearance. Abnormal oesophageal acid exposure increases in severity from endoscopy-negative reflux disease through worsening grades of reflux oesophagitis. Pepsin activity has been shown to be a major determinant of the aggressiveness of refluxate and, in turn, the full activity of gastric pepsin requires a pH below 3. Thus, gastric acid probably exerts a predominantly indirect effect on the pathogenesis of reflux oesophagitis by determining peptic activity. Although bile and other components of small intestinal juice can injure the oesophageal mucosa, these factors are apparently important only in the exceptional patient with very severe reflux disease. Gastric acid hypersecretion is probably also unimportant in the majority of patients. Peptic activity, and hence the aggressiveness of refluxate, are reduced markedly between pH 3 and 4. Achievement of this threshold, pH 3-4, in the daytime is important as, contrary to traditional beliefs, daytime reflux, triggered by food intake, is of the greatest importance in most patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗