Gastric wall tension determines perception of gastric distention

Visible abdominal distension in functional gut disorders: Objective evaluation

BACKGROUND

Visible abdominal distension has been attributed to: (A) distorted perception, (B) intestinal gas accumulation, or (C) abdominophrenic dyssynergia (diaphragmatic push and anterior wall relaxation).

METHODS

A pool of consecutive patients with functional gut disorders and visible abdominal distension included in previous studies (n = 139) was analyzed. Patients (61 functional bloating, 74 constipation-predominant irritable bowel syndrome and 4 with alternating bowel habit) were evaluated twice, under basal conditions and during a self-reported episode of visible abdominal distension; static abdominal CT images were taken in 104 patients, and dynamic EMG recordings of the abdominal walls in 76, with diaphragmatic activity valid for analysis in 35.

KEY RESULTS

(A) Objective evidence of abdominal distension was obtained by tape measure (increase in girth in 138 of 139 patients), by CT imaging (increased abdominal perimeter in 96 of 104 patients) and by abdominal EMG (reduced activity, i.e., relaxation, in 73 of 76 patients). (B) Intestinal gas volume was within ±300 ml from the basal value in 99 patients, and above in 5 patients, who nevertheless exhibited a diaphragmatic descent. (C) Diaphragmatic contraction was detected in 34 of 35 patients by EMG (increased activity) and in 82 of 103 patients by CT (diaphragmatic descent).

CONCLUSIONS AND INFERENCES

In most patients complaining of episodes of visible abdominal distention: (A) the subjective claim is substantiated by objective evidence; (B) an increase in intestinal gas does not justify visible abdominal distention; (C) abdominophrenic dyssynergia is consistently evidenced by dynamic EMG recording, but static CT imaging has less sensitivity.

A novel MRI-based three-dimensional model of stomach volume, surface area, and geometry in response to gastric filling and emptying

BACKGROUND

Gastric motility and accommodation have a critical role in maintaining normal gastrointestinal homeostasis. Different modalities can be adopted to quantify those processes, that is, scintigraphy to measure emptying time and intragastric Barostat for accommodation assessment. However, magnetic resonance imaging (MRI) can assess the same parameters noninvasively without ionizing radiation. Our study aimed to develop a detailed three-dimensional (3D) MRI model of the stomach to describe gastric volumes, surface areas, wall tension distribution, and interobserver agreement.

METHODS

Twelve healthy volunteers underwent an MRI protocol of six axial T2-weighted acquisitions. Each dataset was used to construct a 3D model of the stomach: First, the volumes of the whole stomach, gastric liquid, and air were segmented. After landmark placing, a raw 3D model was generated from segmentation data. Subsequently, irregularities were removed, and the model was divided into compartments. Finally, surface area and 3D geometry parameters (inverse curvatures) were extracted. The inverse curvatures were used as a proxy for wall tension distribution without measuring the intragastric pressure.

KEY RESULTS

The model was able to describe changes in volume and surface geometry for each compartment with a distinct pattern in response to filling and emptying. The surface tension was distributed nonhomogeneously between compartments and showed dynamical changes at various time points.

CONCLUSION & INFERENCES

The presented model offers a detailed tool for evaluating gastric volumes, surface geometry, and wall tension in response to filling and emptying and will provide insights into gastric emptying and accommodation in diseases such as diabetic gastroparesis.

Effect of intracolonic volume on gastric sensory-motor responses in constipation-predominant irritable bowel syndrome

BACKGROUND

Interaction between gut stimuli may induce symptom overlap in patients with functional gastrointestinal disorders. The aim is to determine the effect of increased volumes of colonic contents on gastric sensory/motor responses and satiety in patients with constipation-predominant irritable bowel syndrome (IBS-C) and overlapping dyspeptic symptoms, and a cohort of healthy subjects.

METHODS

In 15 patients with IBS-C and 10 healthy subjects, the effect of real versus sham colonic filling with gas (1080 ml) on gastric sensitivity (measured by stepwise distensions of the stomach), gastric compliance, abdominal perception, and nutrient drink tolerance was studied on separate days.

RESULTS

In healthy subjects, colonic gas filling induced an increment in gastric sensitivity to distension (mean score 2.0 ± 0.2 before, and 3.0 ± 0.4 after; p = 0.038). In IBS, basal sensitivity was greater and remained unchanged after colonic gas filling (score 4.0 ± 0.1 and 3.8 ± 0.3, respectively; p < 0.001 vs. basal in health). Colonic gas infusion induced abdominal symptoms that were significantly greater in IBS-C (score 2.6 ± 0.1) than in health (score 1.7 ± 0.4; p = 0.027), with minor changes in gastric tone, and no changes in gastric compliance in both groups. Colonic filling produced a profound reduction in nutrient drink tolerance in IBS (791 ± 87 ml sham filling, 491 ± 58 ml gas filling; p < 0.001) but only a minor reduction in health (940 ± 70 ml sham filling, 860 ± 94 ml gas filling; p = 0.223).

CONCLUSIONS & INFERENCES

The volume of the colonic contents modulates satiety in patients with IBS-C, due to a general visceral pan-hypersensitivity. These effects should be considered in the choice of treatment for constipation in these patients.

Indentation of a pressurized silicon stomach model - A non-invasive study of gastric wall stiffness and pressurized gastric content stiffness

BACKGROUND AND AIMS

Evaluation of gastric wall stiffness and intragastric pressure is essential for detailed assessments of gastric accommodation. However, non-invasive assessments are needed for large scale clinical studies and none of the existing methods takes abdominal wall effect into the calculation. This study aimed to assess gastric wall stiffness and gastric content stiffness as a proxy for intragastric pressure using novel mechanical modeling and non-invasive indentation tests on a silicon stomach model.

METHODS

A silicon stomach model (scaling 1:1 with the human stomach) was indented using a pressure algometer at intragastric pressures from 0 to 0.8 kPa. Wall thicknesses and luminal cross-sectional areas along the stomach were measured with ultrasound images. The gastric wall stiffness was compared between measurements from tensile tests on strips cut from the silicon stomach and estimations from a shell indentation model. The pressurized gastric content stiffness was predicted from a bonded two-layer axisymmetric half-space indentation model.

RESULTS

The gastric wall stiffness estimated from the shell indentation model showed no difference to measurements from the mechanical tests on the cutting strips (p = 0.14). The predicted gastric content stiffness was strongly associated with the intragastric pressure (r > 0.83, p < 0.001).

CONCLUSIONS

The mechanical model developed in this study can simultaneously predict the gastric wall stiffness and the pressurized gastric content stiffness. In future studies, the method can be applied to reveal intragastric pressure conditions non-invasively via the pressurized gastric content stiffness during gastric accommodation and emptying such as with magnetic resonance imaging.

Psyllium reduces inulin-induced colonic gas production in IBS: MRI and in vitro fermentation studies

OBJECTIVE

Health-promoting dietary fibre including inulin often triggers gastrointestinal symptoms in patients with IBS, limiting their intake. Our aim was to test if coadministering psyllium with inulin would reduce gas production.

DESIGN

A randomised, four-period, four-treatment, placebo-controlled, crossover trial in 19 patients with IBS. Subjects ingested a 500 mL test drink containing either inulin 20 g, psyllium 20 g, inulin 20 g+ psyllium 20 g or dextrose 20 g (placebo). Breath hydrogen was measured every 30 min with MRI scans hourly for 6 hours. Faecal samples from a subset of the patients with IBS were tested using an in vitro fermentation model. Primary endpoint was colonic gas assessed by MRI.

RESULTS

Colonic gas rose steadily from 0 to 6 hours, with inulin causing the greatest rise, median (IQR) AUC_{(0-360 min)} 3145 (848-6502) mL·min. This was significantly reduced with inulin and psyllium coadministration to 618 (62-2345) mL·min (p=0.02), not significantly different from placebo. Colonic volumes AUC_{(0-360 min)} were significantly larger than placebo for both inulin (p=0.002) and inulin and psyllium coadministration (p=0.005). Breath hydrogen rose significantly from 120 min after inulin but not psyllium; coadministration of psyllium with inulin delayed and reduced the maximum increase, AUC_{(0-360 min)} from 7230 (3255-17910) ppm·hour to 1035 (360-4320) ppm·hour, p=0.007.Fermentation in vitro produced more gas with inulin than psyllium. Combining psyllium with inulin did not reduce gas production.

CONCLUSIONS

Psyllium reduced inulin-related gas production in patients with IBS but does not directly inhibit fermentation. Whether coadministration with psyllium increases the tolerability of prebiotics in IBS warrants further study.

TRIAL REGISTRATION NUMBER

NCT03265002.

Gastrointestinal Contributions to the Postprandial Experience

Food ingestion induces homeostatic sensations (satiety, fullness) with a hedonic dimension (satisfaction, changes in mood) that characterize the postprandial experience. Both types of sensation are secondary to intraluminal stimuli produced by the food itself, as well as to the activity of the digestive tract. Postprandial sensations also depend on the nutrient composition of the meal and on colonic fermentation of non-absorbed residues. Gastrointestinal function and the sensitivity of the digestive tract, i.e., perception of gut stimuli, are determined by inherent individual factors, e.g., sex, and can be modulated by different conditioning mechanisms. This narrative review examines the factors that determine perception of digestive stimuli and the postprandial experience.

Gastrointestinal Vagal Afferents and Food Intake: Relevance of Circadian Rhythms

Gastrointestinal vagal afferents (VAs) play an important role in food intake regulation, providing the brain with information on the amount and nutrient composition of a meal. This is processed, eventually leading to meal termination. The response of gastric VAs, to food-related stimuli, is under circadian control and fluctuates depending on the time of day. These rhythms are highly correlated with meal size, with a nadir in VA sensitivity and increase in meal size during the dark phase and a peak in sensitivity and decrease in meal size during the light phase in mice. These rhythms are disrupted in diet-induced obesity and simulated shift work conditions and associated with disrupted food intake patterns. In diet-induced obesity the dampened responses during the light phase are not simply reversed by reverting back to a normal diet. However, time restricted feeding prevents loss of diurnal rhythms in VA signalling in high fat diet-fed mice and, therefore, provides a potential strategy to reset diurnal rhythms in VA signalling to a pre-obese phenotype. This review discusses the role of the circadian system in the regulation of gastrointestinal VA signals and the impact of factors, such as diet-induced obesity and shift work, on these rhythms.

Vagally Mediated Gut-Brain Relationships in Appetite Control-Insights from Porcine Studies

Signals arising from the upper part of the gut are essential for the regulation of food intake, particularly satiation. This information is supplied to the brain partly by vagal nervous afferents. The porcine model, because of its sizeable gyrencephalic brain, omnivorous regimen, and comparative anatomy of the proximal part of the gut to that of humans, has provided several important insights relating to the relevance of vagally mediated gut-brain relationships to the regulation of food intake. Furthermore, its large size combined with the capacity to become obese while overeating a western diet makes it a pivotal addition to existing murine models, especially for translational studies relating to obesity. How gastric, proximal intestinal, and portal information relating to meal arrival and transit are encoded by vagal afferents and their further processing by primary and secondary brain projections are reviewed. Their peripheral and central plasticities in the context of obesity are emphasized. We also present recent insights derived from chronic stimulation of the abdominal vagi with specific reference to the modulation of mesolimbic structures and their role in the restoration of insulin sensitivity in the obese miniature pig model.

The role of diet in the pathophysiology and management of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic gastrointestinal (GI) disorder that reportedly affects 5% to 20% of the world population. The etiology of IBS is not completely understood, but diet appears to play an important role in its pathophysiology. Asian diets differ considerably from those in Western countries, which might explain differences in the prevalence, sex, and clinical presentation seen between patients with IBS in Asian and Western countries. Dietary regimes such as a low-fermentable oligo-, di-, monosaccharides, and polyols (FODMAP) diet and the modified National Institute for Health and Care Excellence (NICE) diet improve both symptoms and the quality of life in a considerable proportion of IBS patients. It has been speculated that diet is a prebiotic for the intestinal microbiota and favors the growth of certain bacteria. These bacteria ferment the dietary components, and the products of fermentation act upon intestinal stem cells to influence their differentiation into enteroendocrine cells. The resulting low density of enteroendocrine cells accompanied by low levels of certain hormones gives rise to intestinal dysmotility, visceral hypersensitivity, and abnormal secretion. This hypothesis is supported by the finding that changing to a low-FODMAP diet restores the density of GI cells to the levels in healthy subjects. These changes in gut endocrine cells caused by low-FODMAP diet are also accompanied by improvements in symptoms and the quality of life.

Correction of Dyssynergic Defecation, but Not Fiber Supplementation, Reduces Symptoms of Functional Dyspepsia in Patients With Constipation in a Randomized Trial

BACKGROUND & AIMS

Patients with functional dyspepsia are believed to have increased sensitivity of the gastrointestinal tract, and some also have functional constipation. We investigated whether in patients with functional dyspepsia, correction of dyssynergic defecation can reduce postprandial fullness.

METHODS

We performed a parallel trial at 2 referral centers in Spain, from June 2016 through January 2018 of 50 patients who fulfilled the Rome IV criteria for functional dyspepsia with postprandial distress syndrome and functional constipation and dyssynergic defecation. After a 2-week pretreatment phase, the patients were randomly assigned to groups that learned to correct dyssynergic defecation (2-3 sessions of biofeedback combined with instructions for daily exercise; n = 25) or received dietary fiber supplementation (3.5 g plantago ovata per day; n = 25) for 4 weeks. The primary outcome was change in postprandial abdominal fullness, measured daily on a scale of 0-10, during the last 7 days treatment phase vs the last 7 days of the pretreatment phase. Anal gas evacuations were measured (by an event marker) during the last 2 days of the pretreatment vs treatment phases.

RESULTS

Biofeedback treatment corrected dyssynergic defecation in 19/25 patients; corrected dyssynergic defection reduced postprandial fullness by 22%±1% in these patients (P < .001), and reduced the number of anal evacuations by 21%±8% (P = .009). Fiber supplementation did not reduce postprandial fullness or anal evacuations (P ≤ .023 between groups for both parameters in the intent to treat analysis).

CONCLUSIONS

Diagnosis and correction of dyssynergic defecation reduces dyspeptic symptoms by more than 20% in patients with functional dyspepsia and associated constipation. Dietary fiber supplementation does not reduce symptoms in these patients. ClinicalTrials.gov no: NCT02956187.

Gastrointestinal Sensing of Meal-Related Signals in Humans, and Dysregulations in Eating-Related Disorders

The upper gastrointestinal (GI) tract plays a critical role in sensing the arrival of a meal, including its volume as well as nutrient and non-nutrient contents. The presence of the meal in the stomach generates a mechanical distension signal, and, as gastric emptying progresses, nutrients increasingly interact with receptors on enteroendocrine cells, triggering the release of gut hormones, with lipid and protein being particularly potent. Collectively, these signals are transmitted to the brain to regulate appetite and energy intake, or in a feedback loop relayed back to the upper GI tract to further adjust GI functions, including gastric emptying. The research in this area to date has provided important insights into how sensing of intraluminal meal-related stimuli acutely regulates appetite and energy intake in humans. However, disturbances in the detection of these stimuli have been described in a number of eating-related disorders. This paper will review the GI sensing of meal-related stimuli and the relationship with appetite and energy intake, and examine changes in GI responses to luminal stimuli in obesity, functional dyspepsia and anorexia of ageing, as examples of eating-related disorders. A much better understanding of the mechanisms underlying these dysregulations is still required to assist in the development of effective management and treatment strategies in the future.

A comparison of various intragastric balloons for the assessment of gastric motility

BACKGROUND

There is a clear need for a novel method to readily assess gastric motility in daily clinical practice.

METHODS

In a crossover design, 10 noncompliant balloons of different shape and volume (25-350 mL), attached to a classic feeding tube, were introduced in the stomach of eight healthy volunteers. In the same experiment, a High-Resolution Manometry (HRM) catheter was positioned throughout the stomach. Gastric motility was recorded during fasting (2 hours) and liquid nutrient administration (30 minutes). Motility was quantified using a peak detection algorithm. Symptoms were recorded throughout the experiment using visual analog scales (100 mm). Results are presented as mean ± SD.

KEY RESULTS

The % time during which motility-induced pressure increments could be detected with HRM but not by the balloon varied from 42 ± 24% in the smallest (25 mL) balloon to 1 ± 1% in the 330 mL balloon. On the other hand, bloating, discomfort and nausea scores were 0 ± 0, 0 ± 0 and 2 ± 5 mm, respectively, for the smallest balloon (25 mL) while these scores were 28 ± 38, 13 ± 30, and 38 ± 30 mm, respectively, for the largest balloon (350 mL). A phase III contraction pattern was consistently evoked in balloons with a volume >200 mL.

CONCLUSION

Gastric motility could be assessed more accurately with larger volume balloons, while epigastric symptoms were evoked with increasing balloon volume. The optimal balloon to measure gastric motility has a 5 cm diameter and is 11 cm long (210 mL). A nasogastric balloon catheter can now be developed that enables relatively easy monitoring of gastric motility in patients with epigastric symptoms.

What Is the Future of Impedance Planimetry in Gastroenterology?

The gastrointestinal (GI) tract is efficient in transporting ingested material to the site of delivery in healthy subjects. A fine balance exists between peristaltic forces, the mixing and delivery of the contents, and sensory signaling. This fine balance is easily disturbed by diseases. It is mandatory to understand the pathophysiology to enhance our understanding of GI disorders. The inaccessibility and complex nervous innervation, geometry and mechanical function of the GI tract make mechanosensory evaluation difficult. Impedance planimetry is a distension technology that assesses luminal geometry, mechanical properties including muscle dynamics, and processing of nociceptive signals from the GI tract. Since standardized models do not exist for GI muscle function in vivo, models, concepts, and terminology must be borrowed from other medical fields such as cardiac mechanophysiology. The review highlights the impedance planimetric technology, muscle dynamics assessment, and 3 applied technologies of impedance planimetry. These technologies are the multimodal probes that assesses sensory function, the functional luminal imaging probe that dynamically measures the geometry of the lumen it distends, and Fecobionics that is a simulated feces providing high-resolution measurements during defecation. The advanced muscle analysis and 3 applied technologies can enhance the quality of future interdisciplinary research for gaining more knowledge about mechanical function, sensory-motor disorders, and symptoms. This is a step in the direction of individualized treatment for GI disorders based on diagnostic subtyping. There seems to be no better alternatives to impedance planimetry, but only the functional luminal imaging probe is currently commercially available. Wider use depends on commercialization of the multimodal probe and Fecobionics.

The predictive value of hunger score on gastric evacuation after oral intake of carbohydrate solution

BACKGROUND

Surgical patients are asked to fast for a sufficient duration to ensure that the amount of residual liquid in the stomach is within the safe range, thereby reducing the risk of gastric reflux perioperatively. The authors hypothesized that subjective hunger numerical rating scale (NRS) score could also help assess the process of gastric emptying and determine the amount of fluid remaining in the stomach.

METHODS

The current study consisted of healthy volunteers recruited by advertisement and mutual introduction. Participants were asked to rate their subjective hunger feeling every 30 min after oral administration of 8 mL/kg carbohydrate nutrient solution that contained 10% maltodextrin and 2.5% sucrose. Consecutively, the gastric residual fluid was measured by magnetic resonance imagining (MRI). The Spearman's correlation coefficient, the ROC curves and the stepwise regression were used to analyze the predictive value of NRS for the gastric emptying process.

RESULTS

The cohort consisted of 29 healthy volunteers enrolled in this study. The area under ROC curves estimated by the NRS score for the gastric residual volume of 2 mL/kg, 1 mL/kg, and 0.5 mL/kg were AUC2.0 = 0.78, AUC1.0 = 0.76, and AUC0.5 = 0.72, respectively. The correlation coefficient between the NRS score and the residual liquid in the stomach was -0.57 (P < 0.01). The correlation coefficient between the increase of the NRS score and the decrease of gastric liquid residual volume was 0.46 (P < 0.01). The standardized estimate of NRS score for the residual volume was -0.18 (P < 0.01) and the standardized estimate of fasting time was -0.73 (P < 0.01).

CONCLUSIONS

The subjective hunger NRS score can not accurately predict the gastric residual volume, but it can provide a reference for clinicians to judge the gastric emptying process and it should be used as a second check after oral intake of clear fluids before surgery according to the new fasting protocol.

Effect of prucalopride on intestinal gas tolerance in patients with functional bowel disorders and constipation

BACKGROUND AND AIM

Patients with functional bowel disorders develop gas retention and symptoms in response to intestinal gas loads that are well tolerated by healthy subjects. Stimulation of 5HT-4 receptors in the gut has both prokinetic and antinociceptive effects. The aim of this study is to determine the effect of prucalopride, a highly selective 5HT-4 agonist, on gas transit and tolerance in women with functional bowel disorders complaining of constipation.

METHODS

Twenty-four women with functional bowel disorders complaining of constipation were included in the study. Patients were studied twice on separate days in a cross-over design. On each study day, an intestinal gas challenge test was performed. During the five previous days, prucalopride (2 mg/day) or placebo was administered. Abdominal symptoms, stool frequency, and stool consistency were recorded during the treatment period on daily questionnaires.

RESULTS

During the gas challenge test, prucalopride did not decrease the volume of gas retained in the subset of patients who had significant gas retention (≥ 200 mL) while on placebo. However, in those patients who had increased symptoms during the gas test (≥ 3 on a 0 to 6 scale) when on placebo, prucalopride did significantly reduce the perception of symptoms (2.3 ± 0.5 mean score vs 3.5 ± 0.3 on placebo; P = 0.045). During the treatment period with prucalopride, patients exhibited an increase in the total number of bowel movements and decreased stool consistency compared with placebo.

CONCLUSION

Prucalopride reduces abdominal symptoms without modifying gas retention when patients with functional bowel disorders are challenged with the gas transit and tolerance test. European Clinical Trials Database (EudraCT2011-006354-86).

Distinct Abnormalities of Small Bowel and Regional Colonic Volumes in Subtypes of Irritable Bowel Syndrome Revealed by MRI

OBJECTIVES

Non-invasive biomarkers which identify different mechanisms of disease in subgroups of irritable bowel syndrome (IBS) could be valuable. Our aim was to seek useful magnetic resonance imaging (MRI) parameters that could distinguish each IBS subtypes.

METHODS

34 healthy volunteers (HV), 30 IBS with diarrhea (IBS-D), 16 IBS with constipation (IBS-C), and 11 IBS with mixed bowel habit (IBS-M) underwent whole-gut transit and small and large bowel volumes assessment with MRI scans from t=0 to t=360 min. Since the bowel frequency for IBS-M were similar to IBS-D, IBS-M and IBS-D were grouped together and labeled as IBS non-constipation group (IBS-nonC).

RESULTS

Median (interquartile range): fasting small bowel water content in IBS-nonC was 21 (10-42), significantly less than HV at 44 ml (15-70), P<0.01 as was the postprandial area under the curve (AUC) P<0.01. The fasting transverse colon volumes in IBS-C were significantly larger at 253 (200-329) compared with HV, IBS-nonC whose values were 165 (117-255) and 198 (106-270) ml, respectively, P=0.02. Whole-gut transit time for IBS-C was prolonged at 69 (51-111), compared with HV at 34 (4-63) and IBS-D at 34 (17-78) h, P=0.03. Bloating score (VAS 0-10 cm) correlated with transverse colon volume at t=405 min, Spearman r=0.21, P=0.04.

CONCLUSIONS

The constricted small bowel in IBS-nonC and the dilated transverse colon in IBS-C point to significant differences in underlying mechanisms of disease.

Effects of scFOS on the composition of fecal microbiota and anxiety in patients with irritable bowel syndrome: a randomized, double blind, placebo controlled study

BACKGROUND

Short-chain fructooligosaccharides (scFOS) have beneficial effects in subjects with minor digestive complaints, but the potential mechanisms involved have not been elucidated. The aim of the study was to evaluate changes in rectal sensitivity related to the clinical effects of scFOS in a selected group of patients with irritable bowel syndrome (IBS) and rectal hypersensitivity.

METHODS

In 79 IBS patients (defined by Rome III criteria) with rectal hypersensitivity (defined as discomfort threshold ≤44 g) a parallel, placebo-controlled, randomized, and double-blind study was performed to assess the effects of dietary supplementation (5 g d^-1 ) with scFOS vs placebo for 4 weeks on rectal sensitivity (primary outcome: tolerance to increasing wall tension applied by a tensostat), clinical outcomes (IBS, anxiety/depression and quality of life scores) and composition of fecal microbiota.

KEY RESULTS

Rectal discomfort threshold, and IBS and quality of life scores, significantly improved during treatment, but in a similar manner in both scFOS and placebo groups; a post-hoc analysis showed that the effect of scFOS on rectal sensitivity was more pronounced in constipation-predominant-IBS patients (P=.051 vs placebo). Contrary with placebo, scFOS significantly reduced anxiety scores and increased fecal Bifidobacteria (P<.05 for both) without modifying other bacterial groups.

CONCLUSIONS & INTERFENCES

The effect of scFOS on anxiety may be related to modulation of the gut microbiota; demonstration of effects of scFOS on rectal sensitivity may require higher doses and may depend on the IBS subgroup.

Upper GI Disorders: Pathophysiology and Current Therapeutic Approaches

Symptoms referable to the upper digestive tract are associated with abnormalities of upper gastric neuromuscular function including abnormalities of motility, sensation, and absorption. Of the upper digestive tract, the stomach is of particular importance in its role in symptom generation and is highlighted in this chapter. Gastric symptoms can be associated with alterations in the rates of gastric emptying, impaired accommodation, heightened gastric sensation, or alterations in gastric myoelectrical activity and contractility. Treatment of gastric neuromuscular disorders requires an understanding of pathophysiology of the disorders, the appropriate use and interpretation of diagnostic tests, and the knowledge of effective treatment options. This chapter covers the pathophysiology and current treatment approaches to disorders of the upper gastrointestinal tract, focusing on classic disorders of the stomach, particularly gastroparesis and functional dyspepsia.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Diabetic neuropathy in the gut: pathogenesis and diagnosis

The activity of the digestive tract is usually regulated to match its content: physiological stimuli in the gut induce modulatory reflexes that control digestive function so that digestion is normally not perceived. However, under certain circumstances, digestive stimuli may activate sensory afferents and give rise to conscious sensations. Both reflex and sensory signals are modulated by a balance of excitatory and inhibitory mechanisms. Patients with diabetes may develop a neuropathy affecting the control of gastric and/or intestinal motor function and the sensory innervation as well. During fasting the stomach is contracted and relaxes to accommodate a meal. After ingestion the stomach progressively recontracts and this contraction gently produces gastric emptying. Impairment of excitatory pathways affects the contraction of the stomach, which may result in delayed gastric emptying and vomiting of retained food. Conversely, alteration of the inhibitory neural pathways results in impaired relaxation of the stomach in response to a meal; in this case increased wall tension may produce early satiation, fullness and nausea. Diabetic neuropathy may distort the control of intestinal motility, which can lead to diverse symptoms such as diarrhoea, constipation, intestinal distension and abdominal pain. Neuropathy in diabetes may also affect the sensory nerves of the gut, and depending on which pathways are involved, perception may be increased or reduced. In summary, in patients with diabetic neuropathy, disorders of gut motor function are associated with sensory abnormalities, and the combination of impaired pathways determines the clinical consequences. This review summarises a presentation given at the 'Diagnosis and treatment of autonomic diabetic neuropathy in the gut' symposium at the 2015 annual meeting of the EASD. It is accompanied by another mini-review on a topic from this symposium (by Hans Törnblom, DOI: 10.1007/s00125-015-3829-9 ) and a commentary by the Session Chair, Péter Kempler (DOI: 10.1007/s00125-015-3826-y ).

Fundamentals of Neurogastroenterology: Physiology/Motility - Sensation

The fundamental gastrointestinal functions include motility, sensation, absorption, secretion, digestion and intestinal barrier function. Digestion of food and absorption of nutrients normally occurs without conscious perception. Symptoms of functional gastrointestinal disorders are often triggered by meal intake suggesting abnormalities in the physiological processes are involved in the generation of symptoms. In this manuscript, normal physiology and pathophysiology of gastrointestinal function, and the processes underlying symptom generation are critically reviewed. The functions of each anatomical region of the digestive tract are summarized. The pathophysiology of perception, motility, mucosal barrier, and secretion in functional gastrointestinal disorders as well as effects of food, meal intake and microbiota on gastrointestinal motility and sensation are discussed. Genetic mechanisms associated with visceral pain and motor functions in health and functional gastrointestinal disorders are reviewed. Understanding the basis for digestive tract functions is essential to understand dysfunctions in the functional gastrointestinal disorders.

The stomach in health and disease

The stomach is traditionally regarded as a hollow muscular sac that initiates the second phase of digestion. Yet this simple view ignores the fact that it is the most sophisticated endocrine organ with unique physiology, biochemistry, immunology and microbiology. All ingested materials, including our nutrition, have to negotiate this organ first, and as such, the stomach is arguably the most important segment within the GI tract. The unique biological function of gastric acid secretion not only initiates the digestive process but also acts as a first line of defence against food-borne microbes. Normal gastric physiology and morphology may be disrupted by Helicobacter pylori infection, the most common chronic bacterial infection in the world and the aetiological agent for most peptic ulcers and gastric cancer. In this state-of-the-art review, the most relevant new aspects of the stomach in health and disease are addressed. Topics include gastric physiology and the role of gastric dysmotility in dyspepsia and gastroparesis; the stomach in appetite control and obesity; there is an update on the immunology of the stomach and the emerging field of the gastric microbiome. H. pylori-induced gastritis and its associated diseases including peptic ulcers and gastric cancer are addressed together with advances in diagnosis. The conclusions provide a future approach to gastric diseases underpinned by the concept that a healthy stomach is the gateway to a healthy and balanced host. This philosophy should reinforce any public health efforts designed to eradicate major gastric diseases, including stomach cancer.

Abdominothoracic mechanisms of functional abdominal distension and correction by biofeedback

BACKGROUND & AIMS

In patients with functional gut disorders, abdominal distension has been associated with descent of the diaphragm and protrusion of the anterior abdominal wall. We investigated mechanisms of abdominal distension in these patients.

METHODS

We performed a prospective study of 45 patients (42 women, 24-71 years old) with functional intestinal disorders (27 with irritable bowel syndrome with constipation, 15 with functional bloating, and 3 with irritable bowel syndrome with alternating bowel habits) and discrete episodes of visible abdominal distension. Subjects were assessed by abdominothoracic computed tomography (n = 39) and electromyography (EMG) of the abdominothoracic wall (n = 32) during basal conditions (without abdominal distension) and during episodes of severe abdominal distension. Fifteen patients received a median of 2 sessions (range, 1-3 sessions) of EMG-guided, respiratory-targeted biofeedback treatment; 11 received 1 control session before treatment.

RESULTS

Episodes of abdominal distension were associated with diaphragm contraction (19% ± 3% increase in EMG score and 12 ± 2 mm descent; P < .001 vs basal values) and intercostal contraction (14% ± 3% increase in EMG scores and 6 ± 1 mm increase in thoracic antero-posterior diameter; P < .001 vs basal values). They were also associated with increases in lung volume (501 ± 93 mL; P < .001 vs basal value) and anterior abdominal wall protrusion (32 ± 3 mm increase in girth; P < .001 vs basal). Biofeedback treatment, but not control sessions, reduced the activity of the intercostal muscles (by 19% ± 2%) and the diaphragm (by 18% ± 4%), activated the internal oblique muscles (by 52% ± 13%), and reduced girth (by 25 ± 3 mm) (P ≤ .009 vs pretreatment for all).

CONCLUSIONS

In patients with functional gut disorders, abdominal distension is a behavioral response that involves activity of the abdominothoracic wall. This distension can be reduced with EMG-guided, respiratory-targeted biofeedback therapy.

Digestive, cognitive and hedonic responses to a meal

BACKGROUND

Gut dysfunctions may be associated to digestive symptoms. We hypothesized that the gut can also originate pleasant sensations, and wished to demonstrate the hedonic component of the digestive response to a meal.

METHODS

Healthy subjects (n = 42) were evaluated during basal fasting conditions and during experimentally induced fullness sensation (either by gastric distension or duodenal nutrient infusion). In each set of studies, a 240 mL test meal (12 kcal broth) and water, as inert control meal, were administered on separate days in a randomized, cross-over design. Gastric accommodation, the cognitive response and the hedonic dimension (both by 10 score scales) were measured 9 min before and 60 min after the meal.

KEY RESULTS

In basal conditions, the test meal induced a significantly greater gastric relaxation than the control meal (166 ± 28 mL isotonic volume increase 67 ± 14 mL; p = 0.002). Both meals induced epigastric fullness (3.8 ± 0.7 score and 3.2 ± 0.8 score, respectively; p = 0.740), but contrary to the inert meal, with the active meal this conscious sensation had a pleasant dimension (digestive comfort increase by 1.3 ± 0.6 score with active meal vs -1.1 ± 0.6 decrease with inert meal; p = 0.015). Experimentally induced fullness was associated to a decrease in digestive well-being or abdominal discomfort, which improved only after the active meal but not the inert meal.

CONCLUSIONS & INFERENCES

When appropriate conditions are met, the response to a meal includes a hedonic dimension involving pleasant sensation of digestive well-being.

Aerated drinks increase gastric volume and reduce appetite as assessed by MRI: a randomized, balanced, crossover trial

BACKGROUND

Compared with nonaerated, isocaloric controls, aerated foods can reduce appetite throughout an entire dieting day. Increased gastric volumes and delayed emptying are possible but unexplored mechanisms.

OBJECTIVE

We tested the hypothesis that aerated drinks (foams) of differing gastric stability would increase gastric distension and reduce appetite compared with a control drink.

DESIGN

In a randomized, balanced, crossover trial, 18 healthy male participants consumed the following 3 skimmed-milk-based test products (all 110 kcal): 2 drinks aerated to foams by whipping (to 490 mL), one drink that was stable in the stomach [stable foam (SF)], and one drink that was less stable in the stomach [less-stable foam (LSF)], and a nonaerated drink [liquid control (LC); 140 mL]. Over 4 h, stomach contents (foam, air, and liquid) were imaged using magnetic resonance imaging (MRI), and self-reported appetite ratings were collected and quantified by the area under the curve or time to return to baseline (TTRTB).

RESULTS

Compared with the LC, both foams caused significantly increased gastric volumes and reduced hunger (all P < 0.001). Compared with the LSF, SF further produced a significantly slower decrease in the total gastric content (P < 0.05) and foam volume (P < 0.0001) and a longer TTRTB (197 compared with 248 min, respectively; P < 0.05), although the hunger AUC was not statistically different. Results for other appetite scales were similar.

CONCLUSIONS

With this MRI trial, we provide novel insights on the gastrointestinal behavior of aerated drinks by measuring separate volumes of foam, liquid, and air layers in the stomach. Appetite suppression induced by foams could largely be explained by effects on gastric volumes and emptying, which may be further enhanced by foam stability. This trial was registered at clinicaltrials.gov as NCT01690182.

Gastrointestinal dysfunction in liver cirrhosis

Patients with liver cirrhosis exhibit several features of gut dysfunction which may contribute to the development of cirrhosis complications as well as have an impact on nutritional status and health-related quality of life. Gastrointestinal symptoms are common in cirrhosis and their pathophysiology probably involves factors related to liver disease severity, psychological distress, and gut dysfunction (e.g., increased gastric sensitivity to distension and delayed gut transit). They may lead to reduced food intake and, thus, may contribute to the nutritional status deterioration in cirrhotic patients. Although tense ascites appears to have a negative impact on meal-induced accommodation of the stomach, published data on gastric accommodation in cirrhotics without significant ascites are not unanimous. Gastric emptying and small bowel transit have generally been shown to be prolonged. This may be related to disturbances in postprandial glucose, insulin, and ghrelin levels, which, in turn, appear to be associated to insulin resistance, a common finding in cirrhosis. Furthermore, small bowel manometry disturbances and delayed gut transit may be associated with the development of small bowel bacterial overgrowth. Finally, several studies have reported intestinal barrier dysfunction in patients with cirrhosis (especially those with portal hypertension), which is related to bacterial translocation and permeation of intestinal bacterial products, e.g., endotoxin and bacterial DNA, thus potentially being involved in the pathogenesis of complications of liver cirrhosis.

Fasting and postprandial gastric sensorimotor activity in functional dyspepsia: postprandial distress vs. epigastric pain syndrome

OBJECTIVES

Little information is available on the mechanisms responsible for dyspeptic symptoms in postprandial distress syndrome (PDS), characterized by the presence of prevalently meal-related early satiation and fullness, and the epigastric pain syndrome (EPS), characterized by the prominent symptom of epigastric pain, generally not meal related. In a group of PDS patients, the presence of hypersensitivity to gastric distension in both fasting and postprandial phases was described as the main pathophysiological mechanism; on the contrary, we have no information on the pathophysiology of EPS.

METHODS

Sixty Helicobacter pylori (HP)-negative, irritable bowel syndrome (IBS)-negative, and gastroesophageal reflux disease (GERD)-negative patients with functional dyspepsia according to Rome III criteria underwent symptom, anxiety, depression, and somatization evaluation, gastric barostat test, and gastric emptying time evaluation for solids. Fifteen age- and sex-matched healthy volunteers (HVs) were also enrolled as a control group.

RESULTS

In PDS patients, the prevalence of both fasting and postprandial hypersensitivity was higher than in EPS patients, and the extent of postprandial reduction of discomfort threshold was significantly correlated with symptom severity. In EPS patients, gastric volume at fasting discomfort threshold and fasting compliance were significantly lower than in PDS patients. Gastric emptying time and gastric accommodation were similar between the two dyspeptic groups. Dyspeptic patients showed a higher prevalence of psychiatric disorders than HVs, but the prevalence was similar between PDS and EPS patients.

CONCLUSIONS

Fasting and postprandial hypersensitivity characterize PDS patients and a reduction of gastric compliance is present in EPS patients. However, the pathophysiology of EPS appears more complex than PDS and further studies are needed to analyze central processing and integration of afferent pathways in order to clarify the role of the central nervous system in this condition.

Additive effects of gastric volumes and macronutrient composition on the sensation of postprandial fullness in humans

Background/Objectives:

Intake of food or fluid distends the stomach and triggers mechanoreceptors and vagal afferents. Wall stretch and tension produces a feeling of fullness. Duodenal infusion studies assessing gastric sensitivity by barostat have shown that the products of fat digestion have a greater effect on the sensation of fullness and also dyspeptic symptoms than carbohydrates. We tested here the hypothesis that fat and carbohydrate have different effects on gastric sensation under physiological conditions using non-invasive magnetic resonance imaging (MRI) to measure gastric volumes.

Subjects/Methods:

Thirteen healthy subjects received a rice pudding test meal with added fat or added carbohydrate on two separate occasions and underwent serial postprandial MRI scans for 4.5 h. Fullness was assessed on a 100-mm visual analogue scale.

Results:

Gastric half emptying time was significantly slower for the high-carbohydrate meal than for the high-fat meal, P=0.0327. Fullness significantly correlated with gastric volumes for both meals; however, the change from baseline in fullness scores was higher for the high-fat meal for any given change in stomach volume (P=0.0147), despite the lower energy content and faster gastric emptying of the high-fat meal.

Conclusions:

Total gastric volume correlates positively and linearly with postprandial fullness and ingestion of a high-fat meal increases this sensation compared with high-carbohydrate meal. These findings can be of clinical interest in patients presenting with postprandial dyspepsia whereby manipulating gastric sensitivity by dietary intervention may help to control digestive sensations.

Mechanisms of postprandial abdominal bloating and distension in functional dyspepsia

OBJECTIVE

Patients with irritable bowel syndrome and abdominal bloating exhibit abnormal responses of the abdominal wall to colonic gas loads. We hypothesised that in patients with postprandial bloating, ingestion of a meal triggers comparable abdominal wall dyssynergia. Our aim was to characterise abdominal accommodation to a meal in patients with postprandial bloating.

DESIGN

A test meal (0.8 kcal/ml nutrients plus 27 g/litre polyethylenglycol 4000) was administered at 50 ml/min as long as tolerated in 10 patients with postprandial bloating (fulfilling Rome III criteria for postprandial distress syndrome) and 12 healthy subjects, while electromyographic (EMG) responses of the anterior wall (upper and lower rectus, external and internal oblique via bipolar surface electrodes) and the diaphragm (via six ring electrodes over an oesophageal tube in the hiatus) were measured. Means +/- SD were calculated.

RESULTS

Healthy subjects tolerated a meal volume of 913±308 ml; normal abdominal wall accommodation to the meal consisted of diaphragmatic relaxation (EMG activity decreased by 15±6%) and a compensatory contraction (25±9% increase) of the upper abdominal wall muscles (upper rectus and external oblique), with no changes in the lower anterior muscles (lower rectus and internal oblique). Patients tolerated lower volume loads (604±310 ml; p=0.030 vs healthy subjects) and developed a paradoxical response, that is, diaphragmatic contraction (14±3% EMG increment; p<0.01 vs healthy subjects) and upper anterior wall relaxation (9±4% inhibition; p<0.01 vs healthy subjects).

CONCLUSIONS

In functional dyspepsia, postprandial abdominal distension is produced by an abnormal viscerosomatic response to meal ingestion that alters normal abdominal accommodation.

Gastric sensitivity and reflexes: basic mechanisms underlying clinical problems

Both reflex and sensory mechanisms control the function of the stomach, and disturbances in these mechanisms may explain the pathophysiology of disorders of gastric function. The objective of this report is to perform a literature-based critical analysis of new, relevant or conflicting information on gastric sensitivity and reflexes, with particular emphasis on the comprehensive integration of basic and clinical research data. The stomach exerts both phasic and tonic muscular (contractile and relaxatory) activity. Gastric tone determines the capacity of the stomach and mediates both gastric accommodation to a meal as well as gastric emptying, by partial relaxation or progressive recontraction, respectively. Perception and reflex afferent pathways from the stomach are activated independently by specific stimuli, suggesting that the terminal nerve endings operate as specialized receptors. Particularly, perception appears to be related to stimulation of tension receptors, while the existence of volume receptors in the stomach is uncertain. Reliable techniques have been developed to measure gastric perception and reflexes both in experimental and clinical conditions, and have facilitated the identification of abnormal responses in patients with gastric disorders. Gastroparesis is characterised by impaired gastric tone and contractility, whereas patients with functional dyspepsia have impaired accommodation, associated with antral distention and increased gastric sensitivity. An integrated view of fragmented knowledge allows the design of pathophysiological models in an attempt to explain disorders of gastric function, and may facilitate the development of mechanistically orientated treatments.

In functional dyspepsia, hypersensitivity to postprandial distention correlates with meal-related symptom severity

BACKGROUND & AIMS

Hypersensitivity to gastric distention, an important feature of functional dyspepsia, is assessed by stepwise balloon distention of the proximal stomach in fasting patients. However, symptoms of functional dyspepsia are often worse after a meal, so studies of postprandial balloon distentions might be more relevant. We compared the effects of fasting and postprandial stomach distention in patients with functional dyspepsia.

METHODS

Twenty healthy controls and 62 patients with functional dyspepsia participated in a gastric barostat study at Leuven University Hospital with graded isobaric distentions before and after a liquid meal. On a separate day, all patients underwent a gastric emptying breath test with assessment of postprandial severity of 6 different dyspeptic symptoms scored at 15-minute intervals for 4 hours. For each symptom, a meal-related severity score was obtained by adding all scores; the cumulative symptom score (CSS) was obtained by adding individual symptom severity scores.

RESULTS

In patients, but not in controls, postprandial sensitivity to balloon distention was significantly greater than fasting sensitivity. The CSS and individual symptom scores did not differ between patients with normal or hypersensitivity to fasting distention, but patients who were hypersensitive to postprandial distention had a significantly higher CSS, along with scores for postprandial fullness, bloating, and nausea (all P < .05). On multivariate analysis, hypersensitivity to postprandial distention was associated with hypersensitivity to fasting distention and with impaired accommodation to a meal.

CONCLUSIONS

Postprandial, but not fasting, distention thresholds are related to the severity of meal-related symptoms in patients with functional dyspepsia.

Temperature can influence gastric accommodation and sensitivity in functional dyspepsia with epigastric pain syndrome

BACKGROUND

Functional dyspepsia-epigastric pain syndrome (FD-EPS) is characterized pathophysiologically by visceral hypersensitivity, but the effect of the temperature stimulation on gastric function has been seldom studied.

AIM

The purpose of this study was to investigate the effects of liquid nutrients at different temperatures on the gastric accommodation, sensitivity, and gastric-wall compliance of healthy subjects (HS) and FD-EPS patients.

METHODS

Ten FD-EPS patients (Roma III criteria) and ten HS were recruited into the study. Intragastric pressure (IGP) and gastric perfusion were measured and compared following the administration of liquid nutrients at 37 °C on day 1 and at 8 °C on day 2.

RESULTS

Seven patients developed abdominal discomfort or abdominal pain after being given cold liquid nutrient. The administration of liquid nutrient at 8 °C resulted in an increase of IGP in HS (P=0.044), a significant decrease in gastric perfusion (P<0.0001), a marked increase in IGP (P=0.015), and a dramatic reduction in gastric wall compliance (P=0.012) in patients compared to the effects of liquid nutrient at 37 °C. In addition, IGP in patients was lower than that in HS at 37 °C liquid nutrient (P=0.036), and the gastric perfusion volume in patients at maximal satiety was also significantly reduced at 8 °C liquid nutrient compared with HS (P=0.017).

CONCLUSIONS

Cold stimulation can increase the IGP in HS and FD-EPS patients, elevate the visceral sensitivity and reduce the gastric volume of FD-EPS patients. FD-EPS patients who are sensitive to cold may develop epigastric discomfort or pain.

Sonographic evaluation of proximal gastric accommodation in patients with functional dyspepsia

AIM: To assess the value of ultrasonography (US) in evaluation of proximal gastric accommodation disorder in patients with functional dyspepsia (FD).

METHODS: Between April 2011 and March 2012, 45 patients with FD and 27 healthy volunteers were enrolled in this study. Two-dimensional ultrasound (2DUS) and 3-dimensional ultrasound (3DUS) were performed sequentially to measure proximal gastric area (PGA), maximal proximal gastric diameter (MPGD), and proximal gastric volume (PGV). These values were measured separately in the two groups every other 5 min for a duration of 25 min after the beginning of ingestion of a test meal. Air pocket grading was done separately for images of 2DUS and blocks of 3DUS obtained at five scanning time points.

RESULTS: Both PGA and PGV of patients were significantly smaller than healthy controls (P = 0.000 and 0.002, respectively). Comparing the two parameters between the groups at each time point, the differences were also statistically significant (P = 0.000-0.013), except at 10 min for the PGV (P = 0.077). However, no overall difference was found between the groups in the MPGD measurements (P = 0.114), though it was statistically significant at a 20-minute examination point (P = 0.026). A total of 360 sets or blocks of images were obtained for both 2DUS and 3DUS. For the images analyzed by 2DUS, none were excluded because of gastric gas, and 50 (13.9%) and 310 (86.1%) sets were determined as air pockets grades 1 and 2, respectively. For the images analyzed by 3DUS, 23 (6.4%) blocks were excluded from the measurement due to presence of a large fundus air pocket (grade 3); fifty (13.9%) and 287 (79.7%) blocks were also graded as 1 and 2, respectively.

CONCLUSION: Measurement of both PGA and PGV by 2DUS and 3DUS could be useful for assessment of the proximal gastric accommodation.

Food and symptom generation in functional gastrointestinal disorders: physiological aspects

The response of the gastrointestinal tract (GIT) to ingestion of food is a complex and closely controlled process, which allows optimization of propulsion, digestion, absorption of nutrients, and removal of indigestible remnants. This review summarizes current knowledge on the mechanisms that control the response of the GIT to food intake. During the cephalic phase, triggered by cortical food-related influences, the GIT prepares for receiving nutrients. The gastric phase is dominated by the mechanical effect of the meal volume. Accumulation of food in the stomach activates tension-sensitive mechanoreceptors, which in turn stimulate gastric accommodation and gastric acid secretion through the intrinsic and vago-vagal reflex pathways. After meal ingestion, the tightly controlled process of gastric emptying starts, with arrival of nutrients in the duodenum triggering negative feedback on emptying and stimulating secretion of digestive enzymes through the neural (mainly vago-vagal reflex, but also intrinsic) and endocrine (release of peptides from entero-endocrine cells) pathways. Several types of specialized receptors detect the presence of all main categories of nutrients. In addition, the gastrointestinal mucosa expresses receptors of the T1R and T2R families (taste receptors) and several members of the transient receptor potential channel family, all of which are putatively involved in the detection of specific tastants in the lumen. Activation of nutrient and taste sensors also activates the extrinsic and intrinsic neural, as well as entero-endocrine, pathways. During passage through the small bowel, nutrients are progressively extracted, and electrolyte-rich liquid intestinal content with non-digestible residue is delivered to the colon. The colon provides absorption of the water and electrolytes, storage of non-digestible remnants of food, aboral propulsion of contents, and finally evacuation through defecation.

Abdominal accommodation induced by meal ingestion: differential responses to gastric and colonic volume loads

BACKGROUND

Using an experimental model of colonic gas infusion, we previously showed that the abdominal walls adapt to its content by an active phenomenon of abdominal accommodation. We now hypothesized that abdominal accommodation is a physiological phenomenon, and aimed to confirm that it can be induced by ingestion of a meal; a secondary aim was to determine whether the response to gut filling is region-specific.

METHODS

In healthy subjects (n = 24) a nutrient test meal was administered until tolerated at a rate of 50 mL min(-1). Electromyographic (EMG) activity of the anterior wall (upper and lower rectus, external and internal oblique) was measured via four pairs of surface electrodes, and EMG activity of the diaphragm via intraluminal electrodes on an esophageal tube. To address the secondary aim, the response to gastric filling was compared with that induced by colonic filling (1440 mL 30 min(-1) anal gas infusion; n = 8).

KEY RESULTS

Participants tolerated 927 ± 66 mL of meal (450-1500 mL). Meal ingestion induced progressive diaphragmatic relaxation (EMG reduction by 16 ± 2%; P < 0.01) and selective contraction of the upper abdominal wall (24 ± 2% increase in activity of the upper rectus and external oblique; P < 0.01 for both), with no significant changes in the lower rectus (4 ± 2%) or internal oblique (5 ± 3%). Colonic gas infusion induced a similar response, but with an overall contraction of the anterior wall.

CONCLUSIONS & INFERENCES

Meal ingestion induces a metered and region-specific response of the abdominal walls to accommodate the volume load. Abnormal abdominal accommodation could be involved in postprandial bloating.

Intragastric balloon fundal or antral position affects weight loss and tolerability

BACKGROUND

Intragastric balloons (BIB) are routinely used for weight reduction. They should be placed to the gastric fundus, as this place is believed more effective for achievement of satiety and thus weight reduction. The aim of the present study was to evaluate whether the balloon position may affect 6-month weight loss as well as first-month side-effects, i.e. nausea, vomiting, and gastroesophageal reflux.

METHODS

From a total of 158 BIB-treated obese individuals, 105 females were found eligible, since the balloon in the stomach was found upon removal in the same position (fundus or antrum) placed at the time of insertion. These subjects were divided into fundus and antral groups. Data related to obesity were recorded on day 0 and upon BIB removal, 6 months thereafter. Data related to transient side-effects (nausea, vomiting, gastroesophageal reflux) were recorded on days 0-3, 7, and weekly thereafter, for 1 month.

RESULTS

BIB placed in the antrum was found to have significantly better results on weight loss parameters, while nausea, vomiting (p = 0.02) as well as gastroesophageal reflux still remained up to the fourth week in a relation to the fundus group. Similarly, the rate of gastric distension was found significantly increased (p = 0.001) during the days 1-3 in fundus group in relation to antrum, followed by a progressive decrease in both groups.

CONCLUSIONS

Intragastric balloon placed in the antrum lead to better results in weight reduction but to longer duration of tolerability-related side-effects, i.e., nausea, vomiting, and gastroesophageal reflux.

A novel 3D shape context method based strain analysis on a rat stomach model

The stomach has the ability to change its geometry and volume during digestion. Thus, the stomach shape changes dynamically due to changes in contents and due to pressure from adjacent organs. Full-field strain analysis is therefore important for accurate estimation of the true deformation in this highly non-homogeneous, anisotropic organ. The aim of this study is to introduce a modified non-rigid image registration based 3D shape context method combined with a full-field strain analysis method to describe a distension-induced 3D gastric deformation. The geometry of a normal rat stomach at distension pressures from 0.05 kPa to 0.8 kPa were obtained by ultrasonic scanning. The full-field strain distribution of the 3D gastric model between the reference state and the distended state were computed on the basis of the improved 3D shape context method and full-field strain analysis method. The registered surface showed a good agreement with the real deformed surface for all distension states. However, the errors increased with the distension pressure due to increasing dissimilarity between the deformed and the reference surface. The strain distributions on the stomach surface were non-uniform with the largest deformation in the non-glandular part and the greater and lesser curvature when the pressure was higher than 0.2 kPa. The wall stiffness of the non-glandular part was softer than that of the glandular part. The modelling analysis method which is closely allied with the non-rigid image registration and strain analysis provides a kinematically possible deformation mode of the gastric wall. This method can be potentially used for clinical data estimating the kinematical properties of the human visceral organs in health and disease.

Accommodation of the abdomen to its content: integrated abdomino-thoracic response

BACKGROUND

  We previously showed that changes in intra-abdominal content induce a volume-dependent muscular response of the anterior abdominal wall and the diaphragm. We aimed to determine the contribution of the thorax to abdominal accommodation and the influence of the intra-abdominal expansion rate.

METHODS

  Gas (1440 mL total load) was infused into the colon of nine healthy subjects, while abdomino-thoracic perimeters (by tape measure), electromyography (EMG) activity of the diaphragm (via six ring electrodes over an esophageal tube in the hiatus), intercostals and anterior abdominal wall (via five pairs of surface electrodes) and the position of the diaphragm by ultrasonography were measured. Infusion rates of 24, 48, and 96 mL min(-1) were tested on separate days.

KEY RESULTS

  Gas infusion induced anterior abdominal wall contraction (18 ± 1% EMG increment; P < 0.001) with relatively modest girth increment (4.9 ± 0.9 mm; P = 0.001), diaphragmatic relaxation (by 15 ± 1%; P < 0.001) with cephalad displacement (by 23 ± 6 mm; P = 0.005), and intercostal contraction (by 19 ± 2%; P < 0.001) with increased thoracic perimeter (by 2.0 ± 0.5 mm; P = 0.009). Responses were similar with the three infusion rates.

CONCLUSIONS & INFERENCES

  Accommodation of intra-abdominal loads involves a volume-related integrated abdomino-thoracic response regardless of the expansion rate.

Sigmoid compliance and visceral perception in spinal cord injury patients

Intestinal motor and sensory dysfunctions in traumatic complete or incomplete spinal cord injury (SCI) are frequent and result in altered mechanisms of defecation. The aim of this study is to investigate sigmoid compliance and perception in chronic SCI patients. Sigmoid responses to fixed-tension distentions were assessed using a tensostat in six patients (six men, 42 ± 4 years) with chronic complete transection of the spinal cord (high-SCI; five tetraplegic C5-C7 and one paraplegic T4-T6) and impaired evacuation (i.e. constipation). A group of 10 healthy individuals (six men, 25 ± 1 years) served as controls. SCI patients had higher sigmoid compliance at the highest distention level than the controls (10.3 ± 2.4 vs. 5.1 ± 0.8 ml/mmHg; P<0.05). Perception scores at first sensation were higher in SCI patients (2.3 ± 0.7 vs. 1.1 ± 0.1; P<0.05), but were not different at the highest distention levels (3.7 ± 0.8 vs. 3 ± 1; NS). The most commonly reported sensation by patients was distention/bloating and was referred less commonly to the hypogastrium compared with distention/bloating in controls. An increased sigmoid compliance can be detected in constipated SCI patients. The preservation of some degree of visceral sensations, although abnormally referred, could imply the occurrence of sensory input remodeling at the spinal level.

Postprandial fullness correlates with rapid inflow of gastric content into duodenum but not with chronic gastritis

BACKGROUND

The aim of this study is evaluating the correlation of postprandial fullness with chronic gastritis or rapid inflow of gastric content into duodenum, based on double-contrast barium X-ray imaging.

METHODS

253 healthy subjects who underwent upper gastrointestinal barium X-ray examination were analyzed. Chronic gastritis was judged from mucosal atrophy and hypertrophic thickened folds on barium X-ray images. For the gastric excretion, the tips of barium flow on the single-contrast frontal barium X-ray images of the stomach were classified into four categories; V type (all the barium remained in the stomach), V-H type (some barium had flowed into the duodenum but the tip of barium remained in the proximal half of the duodenal bulb), H-V type (some barium had flowed into the duodenum and the tip of barium was in the distal half of duodenal the bulb, but no barium was observed in the descending part of the duodenum), and H type (some barium had flowed into the descending part of the duodenum). The chi-square test and Cochran-Mantel-Haenzel test were used for evaluation.

RESULTS

Chronic gastritis was observed in 72 subjects, among which 21 subjects (29.2%) presented with postprandial fullness. For the remaining 181 subjects without chronic gastritis, 53 subjects (29.3%) complained of postprandial fullness. There is no significant correlation between chronic gastritis and postprandial fullness (p = 0.973). For the rapid flow of gastric content into duodenum, all the 253 subjects comprised 136 subjects with V type (in the stomach), 40 subjects with V-H type (in the proximal half of the duodenal bulb), 21 subjects with H-V type (in the distal half of the duodenal bulb), and 56 subjects with H type (in the descending part of the duodenum). Postprandial fullness was present in 30 subjects with V type (22.1%), 9 subjects with V-H type (22.5%), 8 subjects with H-V type (38.1%), and 27 subjects with H type (48.2%). There is a distinct correlation between postprandial fullness and gastric barium excretion on barium X-ray imaging (p = 0.002).

CONCLUSIONS

Bothersome postprandial fullness correlates with rapid inflow of gastric content into duodenum, but not with chronic gastritis.

Review article: the role of gastric motility in the control of food intake

BACKGROUND

From a classical point of view, gastric motility acts to clear the stomach between meals, whereas postprandial motility acts to provide a reservoir for food, mixing and grinding the food and to assure a controlled flow of food to the intestines.

AIM

To summarise findings that support the role of gastric motility as a central mediator of hunger, satiation and satiety.

METHODS

A literature review using the search terms 'satiety', 'satiation' and 'food intake' was combined with specific terms corresponding to the sequence of events during and after food intake.

RESULTS

During food intake, when gastric emptying of especially solids is limited, gastric distension and gastric accommodation play an important function in the regulation of satiation. After food intake, when the stomach gradually empties, the role of gastric distension in the determination of appetite decreases and the focus will shift to gastric emptying and intestinal exposure of the nutrients. Finally, we have discussed the role of the empty stomach and the migrating motor complex in the regulation of hunger signals.

CONCLUSIONS

Our findings indicate that gastric motility is a key mediator of hunger, satiation and satiety. More specifically, gastric accommodation and gastric emptying play important roles in the regulation of gastric (dis)tension and intestinal exposure of nutrients and hence control satiation and satiety. Correlations between gastric accommodation, gastric emptying and body weight indicate that gastric motility can also play a role in the long-term regulation of body weight.

Quantification of the effects of the volume and viscosity of gastric contents on antral and fundic activity in the rat stomach maintained ex vivo

AIMS

The aim of this study was to examine the effect of varying the rheological properties of perfusate on the volume and muscular activity of the various compartments of the rat stomach.

METHODS

Image analysis was used to quantify the activity of the ex vivo stomach preparations when perfused according to a ramp profile.

RESULTS

The area of the fundus increased to a greater extent than that of the body when watery or viscous material was perfused. However, initial distension of the corpus was greater and occurred more rapidly when viscous material was perfused. Only the fundus expanded when perfusion followed the administration of verapamil. The frequency of antrocorporal contractions decreased significantly and the amplitude of antrocorporal contractions increased significantly with increase in gastric volume. The velocity of antrocorporal contractions did not vary with gastric volume but varied regionally in some preparations being faster distally than proximally. Neither the frequency, amplitude or velocity of antrocorporal contractions differed when pseudoplastic rather than watery fluid was perfused. However, the characteristics of antrocorporal contractions changed significantly when the stomach was perfused with material with rheological characteristics that induce different patterns of wall tension to those normally encountered. Hence, the mean frequency and speed of propagation of antrocorporal contractions increased and their direction of propagation became inconstant.

Rational Use of Antibiotics in the Treatment of Functional Bowel Disorders

Functional gastrointestinal symptoms such us bloating, fullness, flatulence, diarrhea, and constipation due to irritable bowel syndrome (IBS) were recently attributed to small bowel bacterial overgrowth, a condition depending on the presence of an increased number of bacteria in the small bowel. However, the methodology used to describe this association may be harshly criticized, since it has already been shown to be quite inaccurate. As a result an inappropriate use of antibiotics was consequently generated. In fact, antibiotics could be effective in the treatment of functional complaints, but only in a limited subgroup of patients, characterized by an increase of fermentation at colonic level. In this review, we have examined the papers suggesting a pathophysiological link between IBS and small bowel bacterial overgrowth, underlining its inappropriateness, and put forth our personal view on the rationale for antibiotic use in IBS.

The dysfunctional gut

After many decades debating whether the clinical manifestations of patients with functional digestive symptoms originate "in their minds" or "in their guts," arguments remain strong on both sides of the controversy. However, advances in understanding of gut physiology and pathophysiology, and persuasive evidence on the bidirectionality of the regulatory traffic between the enteric and central nervous systems, are helping to characterize clinical situations in which we can legitimately speak of gut dysfunction, as opposed to others where symptoms are not associated with apparent or detectable gut disturbances and may truly represent somatization of an affective disorder. In this review, we describe available clinically applicable technology, albeit in specialized clinical research units, that may be used to discern whether or not challenging patients have gut sensory or motor disturbances. The practical yield of applying such methods to diagnostic investigation may be substantial, because it establishes a plausible mechanism of disease that may be used in patient management and patient persuasion, to remove uncertainties and to prevent futile repetition of conventional diagnostic tests. By evolving from symptom analysis to mechanism-based diagnosis, our gastroenterology community may progress toward the goal of delivering the full diagnostic spectrum from altered morphology to disturbed function.