The study of gastric mechanics and flow: a Mad Hatter's tea party starting to make sense?

Effect of two-channel gastric electrical stimulation with trains of pulses on gastric motility

AIM: To investigate the effect of two-channel gastric electrical stimulation (GES) with trains of pulses on gastric emptying and slow waves.

METHODS: Seven dogs implanted with four pairs of electrodes and equipped with a duodenal cannula were involved in this study. Two experiments were performed. The first experiment included a series of sessions in the fasting state with trains of short or long pulses, each lasted 10 min. A 5-min recording without pacing was made between two sessions. The second experiment was performed in three sessions (control, single-channel GES, and two-channel GES). The stimulus was applied via the 1st pair of electrodes for single-channel GES (GES via one pair of electrodes located at 14 cm above the pylorus), and simultaneously via the 1st and 3rd channels for two-channel GES (GES via two pairs of electrodes located at 6 and 14 cm above the pylorus). Gastric liquid emptying was collected every 15 min via the cannula for 90 min.

RESULTS: GES with trains of pulses at a pulse width of 4 ms or higher was able to entrain gastric slow waves. Two-channel GES was about 50% more efficient than single-channel GES in entraining gastric slow waves. Two-channel but not single-channel GES with trains of pulses was capable of accelerating gastric emptying in healthy dogs. Compared with the control session, two-channel GES significantly increased gastric emptying of liquids at 15 min (79.0% ± 6.4% vs 61.3% ± 6.1%, P < 0.01), 30 min (83.2% ± 6.3 % vs 68.2% ± 6.9%, P < 0.01), 60 min (86.9% ± 5.5 % vs 74.1% ± 5.9%, P < 0.01), and 90 min (91.0% ± 3.4% vs 76.5% ± 5.9%, P < 0.01).

CONCLUSION: Two-channel GES with trains of pulses accelerates gastric emptying in healthy dogs and may have a therapeutic potential for the treatment of gastric motility disorders.

Determinants of transpyloric fluid transport: a study using combined real-time ultrasound, manometry, and impedance recording

Intraluminal impedance recording has made it possible to record fluid transport across the pylorus during the interdigestive state without filling the stomach. During antral phase II, fluid transport occurs with and without manometrically detectable antral contraction. Our aim was to investigate the relationships between ultrasonographic patterns of antral contraction, manometric pressure waves, and transpyloric fluid transport during antral phase II. Antral wall movements were recorded by real-time ultrasound (US) in eight healthy volunteers (mean age 24 +/- 7 yr) during 17 +/- 5 min of antral phase II. Concomitantly, a catheter positioned across the pylorus, monitored by transmucosal potential difference measurement, recorded five impedance signals (1 antral, 1 pyloric, and 3 duodenal) and six manometric signals (2 antral, 1 pyloric, and 3 duodenal). Antral contractions detected by US at the level of the two antral impedance electrodes were classified according to their association with a pyloric opening or a duodenal contraction. Transpyloric liquid transport events (impedance drop of >40% of the baseline with an antegrade or retrograde propagation) and manometric pressure waves (amplitude and duration) were identified during the whole study and especially during each period of US antral contraction. A total of 110 antral contractions was detected by US. Of these, 79 were also recorded by manometry. Fluid transport across the pylorus was observed in 70.9% of the US-detected antral contractions. Pyloric opening was observed in 98.6% of the contractions associated with fluid transport compared with 50% in the absence of fluid transport (P < 0.05). Antral contractions associated with fluid transport were significantly (P < 0.05) more often propagated to the duodenum (92%) than those without fluid transport (53%). Pressure waves associated with fluid transport were of higher amplitude (208 mmHg, range 22-493) and longer duration (7 s, range 2.5-13.5 s) than those not associated with fluid transport (102 mmHg, range 18-329 mmHg, and 4.1 s, range 2-8.5 s; P < 0.05). The propagation of the antral contractions in the duodenum in US was always associated with a pyloric opening, whereas only 8 of the 25 contractions without duodenal propagation were associated with a pyloric opening (P < 0.05). The presence of duodenal contractile activity before the onset of an antral contraction in US was always accompanied by pyloric opening and with fluid transport in 93.3%, compared with 56.8% in its absence (P < 0.05). In antral phase II, US is the most sensitive technique to detect antral contractions. Transpyloric fluid transport observed in relation to antral contractions occurs mainly in association with contractions of high amplitude and long duration and is associated with pyloric opening and/or duodenal propagation.

Pathophysiological mechanisms of gastroesophageal reflux disease in children

Gastroesophageal reflux (GER) is an extremely common pediatric problem, but only in the past few years have we developed a better understanding of its pathophysiology. This is related to the wider use of investigative tools such as flexible endoscopy, 24-hour pH monitoring, and more recently, micromanometric methods and noninvasive breath tests, which have been particularly useful in infants. This paper reviews our current understanding of the esophageal and gastric mechanisms contributing to the pathophysiology of GER. In this context, we also highlight areas where new therapeutic approaches may be beneficial.

A longitudinal study of gastric emptying and upper gastrointestinal symptoms in patients with diabetes mellitus

PURPOSE

To evaluate the natural history of gastric emptying and upper gastrointestinal symptoms in patients with diabetes mellitus.

SUBJECTS AND METHODS

We enrolled 20 patients (6 men, 14 women) with diabetes mellitus (16 with type 1 diabetes, 4 with type 2 diabetes). Each had measurements of gastric emptying of a solid (100 g of ground beef) and liquid (150 mL of 10% dextrose) meal using scintigraphy, glycemic control (glycosylated hemoglobin [HbA(1c)] and mean blood glucose levels), upper gastrointestinal symptoms, and autonomic nerve function at baseline and after a mean (+/- SD) of 12.3 +/- 3.1 years of follow-up.

RESULTS

There were no differences in mean gastric emptying of the solid component (retention at 100 minutes at baseline: 56% +/- 19% vs. follow-up: 51% +/- 21%, P = 0.23) or the liquid component (time for 50% to empty at baseline: 33 +/- 11 minutes vs. follow-up: 31 +/- 12 minutes, P = 0.71) during follow-up. Mean blood glucose (17.0 +/- 5.6 mmol/L vs. 13.8 +/- 4.9 mmol/L, P = 0.007) and HbA(1c) (8.4% +/- 2.3% vs. 7.6% +/- 1.3%, P = 0.03) levels were lower at follow-up. There was no difference in symptom score (baseline: 3.9 +/- 2.7 vs. follow-up: 4.2 +/- 4.0, P = 0.78). There was evidence of autonomic neuropathy in 7 patients (35%) at baseline and 16 (80%) at follow-up.

CONCLUSION

In patients with diabetes mellitus, we did not observe any marked changes in either gastric emptying or upper gastrointestinal symptoms during a 12-year period.

Patterns of antropyloric motility in fed healthy preterm infants

BACKGROUND

Antropyloric motility is important for regulation of gastric emptying and has not been adequately characterised in premature infants.

AIM

To evaluate fed patterns of antropyloric motility in premature infants.

SUBJECTS

Forty three healthy premature infants, 30-38 weeks of postmenstrual age.

METHODS

Postprandial antropyloric motility was measured using a micromanometric feeding assembly (outer diameter 1.8 mm) incorporating a pyloric sleeve sensor. The occurrence of isolated pyloric pressure waves (IPPWs) and antral pressure wave sequences (PWSs) was characterised. Sequences were further classified as being antegrade, synchronous, antegrade-synchronous, and retrograde according to the direction of propagation.

RESULTS

A total of 7289 pressure wave events were recorded, 48% IPPWs and 52% PWSs (18% antegrade, 12% synchronous, 13% antegrade-synchronous, 2% retrograde, and 7% undefined). IPPWs predominated in the first postprandial hour, peaking at 30-60 minutes. PWSs predominated in the period after one hour postprandially. Mean (SEM) half gastric emptying time was 42 (4) minutes.

CONCLUSIONS

Monitoring of antropyloric motor patterns in healthy premature infants indicates that the neuroregulatory mechanisms responsible for the coordination of antropyloric motility and gastric emptying are well developed by 30 weeks of postmenstrual age.

Pressure-geometry relationship in the antroduodenal region in humans

Understanding of the control mechanisms underlying gastric motor function is still limited. The aim of the present study was to evaluate antral pressure-geometry relationships during gastric emptying slowed by intraduodenal nutrient infusion and enhanced by erythromycin. In seven healthy subjects, antral contractile activity was assessed by combined dynamic magnetic resonance imaging and antroduodenal high-resolution manometry. After intragastric administration of a 20% glucose solution (750 ml), gastric motility and emptying were recorded during intraduodenal nutrient infusion alone and, subsequently, combined with intravenous erythromycin. Before erythromycin, contraction waves were antegrade (propagation speed: 2.7 +/- 1.7 mm/s; lumen occlusion: 47 +/- 14%). Eighty-two percent (51/62) of contraction waves were detected manometrically. Fifty-four percent of contractile events (254/473) were associated with a detectable pressure event. Pressure and the degree of lumen occlusion were only weakly correlated (r(2) = 0.02; P = 0.026). After erythromycin, episodes of strong antroduodenal contractions were observed. In conclusion, antral contractions alone do not reliably predict gastric emptying. Erythromycin induces strong antroduodenal contractions not necessarily associated with fast emptying. Finally, manometry reliably detects ~80% of contraction waves, but conclusions from manometry regarding actual contractile activity must be made with care.

Relationship between ultrasonically detected phasic antral contractions and antral pressure

The relationships between gastric wall motion and intraluminal pressure are believed to be major determinants of flows within and from the stomach. Gastric antral wall motion and intraluminal pressures were monitored in five healthy subjects by concurrent antropyloroduodenal manometry and transabdominal ultrasound for 60 min after subjects drank 500 ml of clear soup. We found that 99% of antral contractions detected by ultrasound were propagated aborally, and 68% of contractions became lumen occlusive at the site of the ultrasound marker. Of the 203 contractions detected by ultrasound, 53% were associated with pressure events in the manometric reference channel; 86% of contractions had corresponding pressure events detectable somewhere in the antrum. Contractions that occluded the lumen were more likely to be associated with a pressure event in the manometric reference channel (P < 0.01) and to be of greater amplitude (P < 0.01) than non-lumen-occlusive contractions. We conclude that heterogeneous pressure event patterns in the antrum occur despite a stereotyped pattern of contraction propagation seen on ultrasound. Lumen occlusion is more likely to be associated with higher peak antral pressure events.

Reflux in children

Gastro-oesophageal reflux (GOR) is an extremely common paediatric problem that often runs a harmless and self-limited course. Physiological GOR however can lead to marked parental anxiety, many unnecessary investigations and often unwarranted and potentially harmful therapeutic interventions. Our ability to better define GOR and gastro-oesophageal reflux disease (GORD) has improved in the past 15 years with a better understanding of the pathophysiology in infants and children due to the development and wider use of flexible endoscopy, 24-hour oesophageal pH monitoring and, more recently, the use of micromanometric methods for studying oesophageal motility. This will be further enhanced in the future with the development of non-invasive breath testing to study gastrointestinal motility and the use of electrical impedance to study fluid movement. Our therapeutic interventions have also improved particularly in the areas of acid suppression, improved surgical techniques and most recently laparoscopic fundoplication. This chapter reviews these advances in the paediatric area especially with regard to pathophysiology, diagnostic testing and therapeutic intervention.

Gastric emptying in diabetes mellitus: relationship to blood-glucose control

The application of novel investigative techniques has established that disordered gastric motility is a frequent complication of diabetes mellitus. Thus, gastric emptying of solid or nutrient liquid meals is abnormal in 30% to 50% of randomly selected outpatients with long-standing type 1 or type 2 diabetes. Delayed gastric emptying occurs more frequently than rapid emptying. There is increasing evidence that disordered gastric motility has a major impact on the management of patients with diabetes mellitus by leading to gastrointestinal symptoms and poor glycemic control. Although both gastroparesis and upper gastrointestinal symptoms have been attributed to irreversible autonomic damage, it is now clear that acute changes in the blood-glucose concentration have a major effect on both gastrointestinal motor function and the perception of sensations arising in the gut. For example, there is an inverse relationship between the rate of gastric emptying and the blood-glucose concentration, so that gastric emptying is slower during hyperglycemia and accelerated during hypoglycemia. This article reviews some issues in the etiology, diagnosis, and management of problems associated with gastric emptying in elderly persons with diabetes mellitus.

Sonographic observations of the gastroduodenal junction in neonatal piglets

Knowledge of the function of the gastroduodenal junction is important, as changes in its motility are associated with gastrointestinal disorders. Sonographic observations were made of the stomach and duodenum of 19 neonatal piglets, 2-6 d of age. Contractions of the stomach and duodenum were identified clearly; the overall rate of gastric contractions was about 4 min-1. The percentage of contractions in which there was a closure of the terminal pyloric antrum and pyloric canal varied, being 57.2% +/- 4.6% in the first postprandial hour and 43.1% +/- 3.0% in the third. Antegrade flow of digesta principally occurred preceding a closure of the pyloric antrum and canal. During contractions of the pyloric antrum, the torus pyloricus moved caudally to fill the lumen of the pyloric canal. Our sonographic method provided a noninvasive technique for studying the form and function of gastroduodenal motility in the neonate, suitable for investigating factors that alter gastric emptying.

Flow across the human pylorus soon after ingestion of food, studied with duplex sonography. Effect of glyceryl trinitrate

BACKGROUND

By means of duplex sonography, gastric emptying can be related to antral motor activity. The aim of this study was to examine gastric emptying in relation to antral contractions during and immediately after ingestion of a liquid meal in healthy subjects and to study the effect of glyceryl trinitrate (GTN) on this early phase of gastric emptying.

METHODS

Ten healthy, non-smoking men (median age, 36 years; range, 29-41 years) were studied twice on separate days, once without drug administration and once after taking a 0.5-mg sublingual GTN tablet 3 min before ingesting 500 ml of a meat soup (20 kcal; Toro). The subjects were investigated during 3 min of fasting, during 3 min of drinking the soup, and during the first 10 min postprandially.

RESULTS

Transpyloric forward flow commenced on average 80 sec and 95 sec after the start of drinking the soup without and with GTN, respectively (P = NS). Non-contractile, pulsatile transpyloric flow (that is, pendulating, transpyloric flow not associated with antral contractions) occurred during episodes of concurrent relaxation of the terminal antrum, the pylorus, and the duodenal bulb. This type of flow occurred mainly just before the start of contractile, pulsatile transpyloric flow (associated with propulsive antral contractions). Initial non-contractile, pulsatile transpyloric flow before commencement of contractile, pulsatile transpyloric flow lasted longer with GTN (188 sec) than without GTN (25 sec) (P < 0.05). Consequently, contractile, pulsatile transpyloric flow commenced later with GTN (302 sec) than without (102 sec) (P < 0.05).

CONCLUSIONS

Non-contractile transpyloric flow seems to be a physiologic phenomenon during the early phase of gastric emptying. GTN prolongs the initial phase of non-contractile, and delays the onset of contractile, pulsatile transpyloric flow.

Effects of fractionated abdominal irradiation on small intestinal motility--studies in a novel in vitro animal model

Disordered small intestinal motility occurs frequently during acute radiation enteritis. However, the characteristics and time course of the motor dysfunction are poorly defined. These parameters were assessed in a novel animal model of radiation enteritis. Ileal pressures were recorded in vitro with perfused micromanometric catheter using an arterially perfused ileal loop in 22 ferrets following fractionated abdominal irradiation (9 doses 2.50 Gy thrice weekly for 3 weeks). Tissue damage was graded histologically. Studies were performed 3 to 29 days after irradiation. Tissue from 7 control animals was also studied. All treated animals developed diarrhoea. Histology showed changes consistent with mild to moderate radiation enteritis. Following irradiation, there was an initial increase in frequency followed by a non-significant reduction in the frequency, but not the amplitude of ileal pressure waves. The frequency of pressure waves showed an inverse relationship with time after radiation (r = -0.634, p < 0.002). There was no relationship between motility and histology. We conclude that abdominal irradiation is associated with a time-dependent reduction in ileal motility which does not correlate with light microscopic changes.

An evaluation of an ambulatory manometry system in assessment of antroduodenal motor activity

While abnormalities in antroduodenal motor function have been documented in both organic and "functional" disorders, controversy surrounds the ideal manometric technique. We sought, therefore, to evaluate a digital solid-state ambulatory system. Sixteen normal volunteers underwent 24-hr recordings of antroduodenal motility. Following catheter placement, a standardized meal was ingested in the laboratory; thereafter, subjects were ambulatory and assumed normal diet and activities. The system was well tolerated; subjects reported that it did not affect their usual activities. Migrating motor complex (MMC) activity was identified in each subject (mean frequency: 4.1 MMCs/24 hr, range 1-8); on average 1.9 (range 0-4, frequency 0.1/hr) occurred while awake and 2.1 (range 0-5, 0.3/hr, P < 0.05 vs awake) during sleep. The fed response was evaluated by calculating a motility index (MI) at 30-min intervals from 30 min before to 120 min following meal ingestion. Postprandially, MI was maximal during the first 30 min following meal ingestion: MI (mean +/- SD) 30 min before vs 30 min after meal in the antrum: 4.16 +/- 1.42 vs 5.33 +/- 0.72 (P < 0.05), duodenum: 4.04 +/- 0.80 vs 4.57 +/- 0.47 (P < 0.05), respectively. None of the other postprandial intervals were significantly different from baseline. There was no significant difference in MI between the standard and ad libitum meals. Retrograde catheter migration (mean 5.6, range 1-10 cm) occurred in relation to all meals: as a consequence, antral recordings were lost following 60% of all meals, thereby limiting meaningful analysis of the antral fed response. We conclude, firstly, that while an ambulatory antroduodenal manometry system is well tolerated and reliably records duodenal motility, postprandial catheter migration limits antral recordings, and, secondly, that a motility index calculated during the first 30 min following an ad libitum meal accurately reflects the fed motor response.

Effects of cisapride on gastric emptying of oil and aqueous meal components, hunger, and fullness

To evaluate the effects of cisapride on gastric emptying of extracellular fat and hunger and fullness 10 volunteers consumed a meal consisting of 60 ml technectium-99m (99mTc)-V-thiocyanate labelled olive oil and 290 ml indium-113m (113mIn) labelled soup after taking cisapride (10 mg four times daily orally) and placebo, each for four days, in randomised, double blind fashion. Gastric emptying was quantified scintigraphically. Hunger and fullness before and after the meal were evaluated using visual analogue scales. Cisapride accelerated gastric emptying of oil and aqueous components by reducing the lag phase mean (SEM) (20.3 (7.0) min v 40.7 (4.1) min (p < 0.05) for oil and 4.1 (2.5) min v 10.0 (3.1) min (p < 0.05) for aqueous). Cisapride had no effect on the post-lag emptying rate of oil. Treatment with cisapride was associated with reduced retention of oil in the proximal stomach (p < 0.05). Subjects were more hungry before ingestion of the meal while receiving cisapride (6.7 (0.9) v 3.9 (0.7), p < 0.001). The scores for hunger at 120 and 180 minutes were inversely related to gastric emptying of oil on both cisapride (r > -0.62, p < 0.05) and placebo (r > -0.86, p < 0.001). Fullness increased after the meal while receiving placebo (p < 0.01), but not cisapride and postprandial fullness was less with cisapride at (30 min; 0.4 (0.3) v 3.3 (1.0), p < 0.05). With placebo, but not cisapride, the score for fullness at 15 minutes was inversely related to emptying of the aqueous phase (r = 0.68, p < 0.05). These results show that in normal volunteers after ingestion of an oil/aqueous meal: (a) postprandial hunger is inversely related to gastric emptying of oil, while fullness is inversely related to gastric emptying of the aqueous phase, (b) cisapride affects the intragastric distribution and accelerates gastric emptying of both oil and aqueous meal components, and (c) cisapride increases preprandial hunger and reduces postprandial fullness.

Evaluation of antral motility in humans using manometry and scintigraphy

Recent studies suggest that scintigraphy can be used to evaluate non-invasively antral motility in humans, although scintigraphic techniques have not yet been compared with more conventional measurements of intraluminal pressures by manometry. Simultaneous scintigraphic and manometric measurements of antral motility were performed in nine healthy volunteers. After intubation with a sleeve/sidehole catheter which incorporated five pressure sideholes located at 1.5 cm intervals spanning the antrum, each subject ingested 100 g minced beef labelled with 100 MBq 99mTc-chicken liver and 150 ml water. Between 40-43, 60-63, 80-83, and 100-103 minutes after meal ingestion, radioisotopic data were acquired in two second frames. Time-activity curves showing antral 'contractions' resulting from wall motion were derived by drawing small regions of interest over the antrum to coincide with the position of the antral manometric sideholes. Scintigraphic contraction rates approximated 3/minute, whereas antral pressure waves that occluded the lumen were less frequent (p < 0.01 for all), particularly in the proximal antrum. The amplitude of wall motion, evaluated scintigraphically, and the amplitude of pressure waves were both inversely related to the distance from the pylorus (r > -0.32, p < 0.05) and antral volume r > -0.29 (p < 0.05). There were significant relationships between the amplitude of contractions assessed scintigraphically and the number of lumen-occlusive antral pressure waves in the distal antrum (r -0.48, p < 0.05) but not in the more proximal antral regions. It is concluded that scintigraphy can detect antral wall motion with greater sensitivity than manometry, particularly in the proximal antrum. As manometry gives information on the amplitude as well as the temporal and spatial organisation of those contractions which result in lumen occlusion, the combination of scintigraphic and manometric techniques in the evaluation of antral motility shows considerable promise.