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Biomedical subjects

D G Thompson

Publications and source records attributed to D G Thompson.

At least 91 records · Page 5Linked to original sources
PubMed1994

Modulation of gastric perception and motility in man. Current concepts and correlation with symptoms.

Gastric function is controlled by central and peripheral modulation. Most often, afferent information from the stomach does not reach conscious level. At extremes of chemical and mechanical stimulation, however, afferent signals are perceived as pain. Whether or not a signal is perceived depends on gating of afferent signals at the levels of both spinal cord and brainstem. Inhibition of gastric tone and peristalsis during perceived discomfort largely results from stimulation via sympathetic neural pathways. These findings may be clinically relevant because upper gastrointestinal symptoms in many dyspeptic patients could be the result of primary afferent neuron dysfunction rather than motor dysfunction.

Afferent Pathways↗
PubMed1994

Esophageal clearance function following treatment of esophagitis.

BACKGROUND/AIMS: To investigate whether healing of the esophagitis was associated with an improvement in esophageal clearance function, 15 patients with endoscopic and histologically confirmed erosive esophagitis were studied both before and after 1-month treatment with 40 mg/day of omeprazole. METHODS: All patients were studied before and after treatment by perfusion manometry to measure esophageal pressures, and a traction measuring device was used to record aboral forces generated by graded intraluminal distension. RESULTS: Before treatment, standard manometry showed reduced lower esophageal sphincter pressures (4 mm Hg [range, 2-9] vs. a control of 12 mm Hg [range, 5-25]; P < 0.01) and distal peristaltic amplitudes (29 mm Hg [range, 5-57] vs. a control of 55 mg Hg [range, 32-90]; P < 0.01). Responses to distension were also abnormal with a higher threshold for induction of contractile activity (12 mL [range, 8.5-14] vs. control values of 5 mL [range, 3-10]; P < 0.01) and weaker clearance forces (5 g [range, 0-80] vs. control values of 20 g [range, 8-90]; P < 0.01). After treatment, all patients showed endoscopic and histological evidence of healing, but not consistent improvement in either lower esophageal sphincter pressure (5 mm Hg [range, 3-7]; P > 0.05 vs. pretreatment) or peristaltic amplitude (35 mm Hg [range, 10-55]) was found. However, responses to distension did improve, with a decrease in distension threshold to 10 mL (range, 7-14; P = 0.04) and enhancement of traction force to 14 g (range, 0-95; P < 0.01). Patients with the worst pretreatment distension responses showed the least improvement with therapy. CONCLUSIONS: Improvement in esophageal clearance can be achieved by the healing of esophagitis, although the capacity for functional benefit appears to be related to the degree of dysfunction present before therapy.

Adult↗
PubMed1994

Beta adrenergic modulation of human upper intestinal propulsive forces.

beta Adrenoceptor blockade is known to accelerate transit through the small intestine without changing either the number or pattern of intestinal contractions. This study therefore tested the hypothesis that an increase in intraluminal aboral propulsive force may contribute to this transit acceleration. Twenty paired studies were performed, in 10 healthy volunteers, after oral administration of either 100 mg atenolol (a selective beta 1 antagonist) or matched dummy tablets according to a double blind, randomised protocol. The frequency of occurrence of, and the propulsive force exerted by, traction events related to intestinal contractions were measured, using a combined traction force detector and manometry assembly. After atenolol, a consistent increase in the force generated per traction event was noted, both for propagating contractions mean (SEM) (12.0 (1.8) g v control 5.9 (0.07) g; p < 0.05) and for stationary (11.6 (1.4) g v control 7.0 (0.7) g; p < 0.05). In contrast no change in the number of traction events was noted (control v atenolol = 1.6 (0.3) v 1.64 (0.4) per min for propagating and 0.7 (0.1) v 0.85 (0.16) per min for stationary contraction; p > 0.05). beta Adrenoceptor blockade thus increases the propulsive force generated by intestinal contractions, possibly by removing a sympathetic neural inhibition of intestinal tone.

Adult↗
PubMed1994

Diminished oesophageal traction forces with swallowing in gastro-oesophageal reflux disease and in functional dysphagia.

Relations between primary oesophageal peristaltic amplitude and traction force were studied in 30 normal volunteers, 12 patients with functional dysphagia, and 48 patients with gastro-oesophageal reflux disease, using a new intraluminal strain gauge device. Forces generated by swallowing in the normal oesophagus were 42 (35-60) g (median and interquartile range), a close positive correlation existing between traction force and contractile amplitude for each subject (r = 0.5 (0.38-0.6). Traction force increased with increasing balloon volume from 62 (50-73) g at 2 ml to 86 (70-105) g at 4 ml (p < 0.05), indicating distension related modulation of peristaltic force. Patients with oesophagitis generated lower traction forces on swallowing 30 (20-40) g compared with the normal subjects (p < 0.01), the degree of impairment being greatest in those patients with the most severe mucosal damage. Patients with gastro-oesophageal reflux without endoscopic oesophagitis also showed abnormal forces (32 22-38) g p < 0.01 v controls), which were similar to those patients with mild oesophagitis but were greater than those with severe oesophagitis (p < 0.05). In patients with functional dysphagia, forces were also impaired (28 (10-60) g p < 0.05 v controls) despite normal standard manometry. Our results show that measurement of the traction force generated by primary peristalsis provides information about oesophageal neuromuscular function that is not demonstrable by manometry alone and can be abnormal in patients with oesophageal symptoms in whom standard techniques are normal.

Adolescent↗
PubMed1994

Abnormal intragastric distribution of food during gastric emptying in functional dyspepsia patients.

Although delayed gastric emptying is found in some patients with functional dyspepsia, there seems to be little relation between rate of emptying and symptoms. This study examined the hypothesis that food maldistribution rather than gastric stasis may equate to symptoms in such patients and used scintigraphic techniques to quantify the partition of gastric contents between proximal and distal stomach during gastric emptying. Eleven patients with functional dyspepsia characterised by chronic severe postprandial bloating without organic abnormality, and 12 healthy volunteers, ingested a standard meal labelled with technetium-99M (99mTc). Serial images of the gastric area in anterior and posterior projections were taken for 90 minutes, regions of interest for proximal, distal, and total stomach were defined, and activity time curves were derived from the geometric means of anterior and posterior counts. Total emptying in patients (median: 46 minutes; range: 30-76) was not significantly different from controls (45 minutes; 28-58) and only three showed delayed gastric emptying. In controls, food remained predominantly in the proximal half of the stomach after ingestion and then redistributed to the distal half. In the patients, however, initial activity in the proximal half after ingestion (48%; 40-65) was significantly lower (p < 0.05) than in controls (60%; 39-73) and distributed more fully to the distal half of the stomach with a peak distal activity (56%; 34-58), which was consistently higher than in controls (36%; 33-42) (p < 0.05). It is concluded that this subgroup of functional dyspepsia patients show abnormal intragastric distribution of food, independent of gastric emptying rate.

Adult↗
PubMed1994

Human small intestinal contractions and aboral traction forces during fasting and after feeding.

Small intestinal intraluminal pressure activity and aboral traction forces were explored in 19 healthy volunteers using a combined manometry and traction force detecting assembly sited in the upper small intestine. Each aboral traction event was classified as being associated with either a propagating or a stationary contraction and its force measured. During phase I no contractions or traction events were seen. During phase II, traction events related to propagating contractions mean (SEM) (2.2 (0.2)/min) and to stationary contractions (0.3 (0.1)/min) generated similar force/event (7.5(0.9 g v 8.7 (1.4) g, p > 0.05). During phase III, all traction events were related to propagating contractions and generated 9.3 (2.4) g force/event (p > 0.05 v phase II). After feeding, traction events related to propagating contractions generated similar force/event to those related to stationary contractions (5.9 (1.0) g v 9.3 (2.7) g, p > 0.05 v each other and v fasting). No consistent pattern was seen in the temporal distribution of the traction events or in the pattern of the amplitude of the force of successive traction events.

Adult↗
PubMed1994

Evaluation of human postprandial antral motor function using ultrasound.

We used high-resolution ultrasound to characterize postprandial antral excursion characteristics in 15 healthy volunteers. Antral circumference was repeatedly measured in the sagittal plane anterior to the abdominal aorta, at 15-min intervals following ingestion of a standard meal. At each recording period, the maximal and minimal antral circumference was noted. In seven volunteers, antral circumference was studied continuously for 5 min at each 15-min recording period to assess the frequency and regularity of antral excursions. Antral circumference increased immediately after meal ingestion from preprandial values of 64 +/- 2.6 (means +/- SE) to 138 +/- 3.1 mm and then gradually decreased with meal emptying to 72 +/- 2.6 mm at 90 min. The continuous recordings of antral images revealed that antral circumference transiently decreased at regular intervals; the interval between successive excursions was 20.1 +/- 0.2 s. There was no change in the excursion interval with emptying. The excursion amplitude decreased from 33 +/- 3.9 mm immediately post-meal ingestion to 13 +/- 1.5 mm at 90 min (r2 = 0.62 +/- 0.07). The ratio between the excursion amplitude and circumference of the relaxed antrum changed only slightly with time (slope = 0.0009 +/- 0.00003). Comparison of repeat studies in 10 volunteers showed a low intra-individual variation for postprandial antral circumference and excursion amplitude.

Adult↗
PubMed1994

Relaxation responses of the human proximal stomach to distension during fasting and after food.

The responses of the human proximal stomach to distension were studied in 22 healthy volunteers using an intragastric polyethylene bag, inflated progressively in 30-ml steps until the limit of tolerated volume was reached. Three successive inflations were carried out during the fasting state followed by a fourth inflation after ingestion of 250 ml of either a nutrient meal or isosmolar saline. The first inflation showed an initial nonlinear pressure rise (slope of logged pressure vs. volume = 114.6 +/- 10.0 log mmHg/ml x 10(-5)), which was then followed by the development of a plateau phase, in which further distension did not increase intragastric pressure. The slopes of the subsequent fasting inflations were significantly lower than that of the first inflation (P < 0.01) but were similar to each other (slope 83.0 +/- 5.4 and 79.8 +/- 5.7 log mmHg/ml x 10(-5)), indicating that distension-induced gastric relaxation had occurred. After saline ingestion, responses to distension were similar to those during the fasted state. After the nutrient meal ingestion, however, the slope decreased to 60.3 +/- 7.7 log mmHg/ml x 10(-5) (P < 0.01 vs. saline), indicating nutrient-induced gastric relaxation. Our study demonstrates that the pressure-volume characteristics of the proximal stomach are modulated both by distension and by the presence of nutrients in the upper gut, which appear to operate independently.

Adult↗
PubMed1994

Esophageal myoelectric responses to magnetic stimulation of the human cortex and the extracranial vagus nerve.

We describe the use of magnetic stimulation of the human motor cortex and the extracranial vagus nerve in the neck to study human esophageal electromyographic (EMG) responses. Diffuse cortical stimulation produced both an early and a late EMG response in the proximal esophagus with latencies of 10.9 +/- 0.5 and 43.4 +/- 4.3 ms, respectively. Increasing the stimulation intensity increased the amplitude and duration, but reduced the latency, of the early response (P < 0.01), whereas the late response remained unchanged. The early response, but not the late response, was facilitated when cortical stimulation was performed during valsalva maneuver. Maximal early response amplitudes were obtained by focal stimulation of either hemisphere 4-8 cm lateral to the vertex. Stimulation of the neck over the extracranial vagus nerve at the angle of the jaw also produced an early and a late EMG response in the proximal esophagus with latencies of 4.3 +/- 0.4 and 56.8 +/- 14.5 ms, respectively. Early responses were also recorded in the midesophagus and distal esophagus from either cortical or vagal stimulation, but amplitudes were smaller and rise times were longer, suggesting passive "volume conduction" from the proximal esophagus. Comparison of laryngeal, pharyngeal, and esophageal early EMG responses showed similar amplitudes and rise times, suggesting that the action potentials were generated locally at each site and that true esophageal responses were being detected.

Adult↗
PubMed1994

Consequences of perinatal asphyxia.

Perinatal asphyxia occurs in 3-9 of every 1,000 births. The risk for perinatal asphyxia is present in every pregnancy. When asphyxia is diagnosed in a newborn, the effects on the infant are potentially life-threatening. Management of the asphyxia focuses on initial stabilization and support based on identified organ system dysfunction as well as support for the infant's family. Long-term outcome for the asphyxiated infant is related to the degree, duration, and resolution of organ system dysfunction.

Asphyxia Neonatorum↗
PubMed1994

Effects of lethal and sublethal concentrations of the herbicide, triclopyr butoxyethyl ester, in the diet of zebra finches.

Lethal and sublethal effects of dietary triclopyr butoxyethyl ester (TBEE) on zebra finches (Poephila guttata Gould) were determined in laboratory experiments conducted between 8 January and 1 May 1991. The 8-day median lethal dietary concentration, LC50 (95% confidence interval), of TBEE to zebra finches was 1,923 (1,627 to 2,277) mg/kg. In the sublethal effects experiment, when birds were exposed to 500 mg/kg TBEE in the diet for 29 days, food consumption and body weight were significantly depressed (P < 0.05). Similar prolonged exposures to 50 and 150 mg/kg TBEE in the diet had no significant effect on food consumption or body weight (P > 0.05). Perch-hopping activity was depressed relative to controls in the 500 mg/kg group, and elevated in the 150 mg/kg group, but neither of these differences was significantly (P > 0.05). Disappearance of TBEE residues from treated seeds over the 29 day experimental period followed an exponential decay model, with half-lives in the order of 15 to 18 days. On the basis of our observation that TBEE had no significant adverse effects at a concentration greater than the maximum expected environmental concentration, we propose that forestry applications of triclopyr at registered dosage rates pose little risk to wild songbirds.

Analysis of Variance↗
PubMed1993

The effect of beta-adrenoreceptor agonists and antagonists on fructose absorption in man.

To explore the effect of beta-adrenoreceptor stimulation and blockade on the extraction of monosaccharide from the upper gut, we first established the malabsorption threshold in 26 normal volunteers using a series of test meals containing varying proportions of fructose and glucose. Incomplete small intestinal extraction and consequent arrival of carbohydrate into the caecum was identified by a rise in exhaled breath hydrogen concentration. The malabsorption threshold varied between individuals from 30 to 80 g fructose (median 40 g) but was reproducible within individuals, with 90% agreement of repeat studies. The malabsorption threshold for an individual was unrelated to body height (tau = 0.007, P > 0.05) or weight (tau = 0.003, P > 0.05) but correlated closely with time to onset of the breath hydrogen rise of a standard meal (tau = 0.70, P < 0.001). Administration of the beta-adrenoreceptor antagonist propranolol (160 mg) reduced the quantity of fructose required to exceed the malabsorption threshold from 45, 30-60 (median and range) to 40, 30-50 g (P = 0.03); administration of the beta-adrenoreceptor agonist isoprenaline (0.015 micrograms.kg/min) increased the quantity of fructose required to exceed the malabsorption threshold by 10 g (55 (50-90) g; P < 0.02). The effect of both drugs correlated closely with their transit effect (tau = 0.79, P < 0.01). A beta-adrenoreceptor mediated pathway thus appears to be capable of influencing the extraction of monosaccharide from the small intestine in normal subjects both under resting and stimulated conditions, probably acting via an effect on upper gastrointestinal motility.

Adrenergic beta-Agonists↗
PubMed1993

Responses of the human esophagus to experimental intraluminal distension.

Contractile and propulsive forces generated in response to intraluminal distension of the human esophagus were measured in 30 volunteers with the use of a novel intraluminal catheter assembly. Distension was achieved by graded inflation of a balloon for periods of 30 s using volumes of air varying between 0 and 12 ml. In the lower esophagus, distension above a threshold volume of 5 (3-10) ml (median and interquartile range) induced a traction force together with contractile activity proximal to the balloon and quiescence distally. Proximal contractile activity and aboral traction force increased with increasing inflation volume, the magnitude of the response being additionally dependent on the site and the length of esophageal wall stimulated. Although the threshold for induction of motor responses was similar at different distension sites, the magnitude of both contractile and traction responses was higher in the distal than in the midesophagus. In the upper esophagus, the contractions induced proximal to the distension propagated aborally, whereas in the lower esophagus nonpropagating proximal contractions were induced. With the use of a dual balloon technique, it was possible to demonstrate that the distal quiescence represented a true descending inhibitory response since inflation of a proximal balloon suppressed the contractile response induced by a distal balloon. These results thus provide a description of the human esophageal response to distension against which responses in disease states can be compared.

Adolescent↗
PubMed1992

Identification of an abnormal esophageal clearance response to intraluminal distention in patients with esophagitis.

Esophageal clearance responses were studied by a new technique comprising a miniature electronic strain gauge attached to an inflatable balloon in 30 normal volunteers and 48 patients with gastroesophageal reflux disease. The pressure changes around the balloon and traction forces acting on the balloon were measured during graded balloon distention (0-12 mL of air for 30 seconds each inflation) in the lower and midesophagus. All normal volunteers responded to distention with development of swallow independent contractions above the balloon [65 mm Hg/30 s (range, 45-100 mm Hg/30 s)] together with generation of an aboral traction force [15 g (range, 9-20 g)]. Patients with reflux esophagitis showed a higher distention threshold for initiation of these responses, induced fewer proximal contractions [24 mm Hg/30 s (range, 0-38 mm Hg/30 s); P less than 0.01 vs. normal], and generated weaker traction forces [4 g (range, 0-6 g) at 10 mL P less than 0.01 vs. normal]. Patients with the most severe esophagitis showed greatest impairment of the clearance response (correlation = 0.7, P less than 0.01) and the greatest esophageal residence of refluxed acid (correlation = 0.5, P less than 0.01). These abnormalities appear to be of relevance to the pathophysiology of esophageal reflux disease although it remains to be determined whether they are the cause, or the result, of the esophagitis.

Adolescent↗
PubMed1992

Review article: adrenergic control of motor and secretory function in the gastrointestinal tract.

The role that the sympathetic nervous system plays in modulating physiological processes in the gastrointestinal tract is becoming clearer. It is now known that motor, secretomotor and vasomotor activity are all modulated independently by the system. Adrenoreceptor stimulation appears to reduce intestinal contraction (except at sphincters), both via alpha-receptors which inhibit neurotransmitter release and also by a direct beta-receptor mediated action on smooth muscle. There is also evidence for tonic activity in the beta-adrenergic pathway, since beta-antagonists tend to increase contraction pressures. In animals alpha-receptor-mediated pathways modulate fluid and electrolyte absorption, and alpha-adrenergic agonists enhance net absorption and reduce net secretion. In man there is also evidence for a beta-adrenergic pathway which controls secretomotor function. Carbohydrate absorption appears to be dependent on activity in a beta-adrenergic pathway, although this may be an indirect effect of changes in motor function. The time course of changes of both secretomotor and motor activity, induced by modulating sympathetic or adrenergic input, differ from the vascular changes indicating that the effects occur independently of each other. The gastrointestinal response to stressors is mediated, in part at least, by the sympathetic nervous system. Differences between individuals are likely to prove important. Since the sympathetic nervous system regulates gastrointestinal function both in the basal state and under stressful conditions, it will have effects on pathophysiological responses. Modification of such responses is likely to ameliorate symptoms, as has already been found for alpha-2-adrenergic agonists which have an antidiarrhoeal action.

Animals↗
PubMed1992

The effect of alpha-1-adrenoreceptor agonist and antagonist administration on human upper gastrointestinal transit and motility.

To explore the role of alpha-1-adrenoreceptor-mediated pathways on human upper gut motor function in vivo, we studied the effects of the alpha-1-agonist phenylephrine and the alpha-1-antagonist thymoxamine on oro-caecal transit and antroduodenal motor activity. Transit was measured using a standard exhaled-breath hydrogen method, and motility was measured by intraluminal manometry. Oro-caecal transit was unaffected by 80 mg thymoxamine [median 63 min (range 35-164 min) vs. control, 65 min (range 30-155 min), P greater than 0.1]. However, phenylephrine (2.4 micrograms/kg/min) consistently delayed oro-caecal transit time to 103 min (50-215 min), P greater than 0.005. Co-administration of thymoxamine abolished this phenylephrine-induced delay. The mean amplitude of antral postprandial contractions was reduced by phenylephrine from 29 (13-37) to 10 (3-13) mmHg (P less than 0.02). In contrast, neither the pattern nor the mean inter-contraction interval was altered. Responses to phenylephrine in the duodenum were similar to those in the antrum, with reduction in amplitude from 12 (3-18) to 6 (5-13) mmHg without alteration in the pattern or interval between contractions. Nutrient transit through the upper gut can thus be inhibited via activation of an alpha-1-adrenoreceptor-mediated pathway. Failure of alpha-1-antagonist administration to alter oro-caecal transit suggests that this pathway is not tonically active, and it is therefore unlikely to play a major role in nutrient passage under normal circumstances.

Adrenergic alpha-Agonists↗