Sites of symptomatic gas retention during intestinal lipid perfusion in healthy subjects

Abdominothoracic Postural Tone Influences the Sensations Induced by Meal Ingestion

Postprandial objective abdominal distention is frequently associated with a subjective sensation of abdominal bloating, but the relation between both complaints is unknown. While the bloating sensation has a visceral origin, abdominal distention is a behavioral somatic response, involving contraction and descent of the diaphragm with protrusion of the anterior abdominal wall. Our aim was to determine whether abdominal distention influences digestive sensations. In 16 healthy women we investigated the effect of intentional abdominal distention on experimentally induced bloating sensation (by a meal overload). Participants were first taught to produce diaphragmatic contraction and visible abdominal distention. After a meal overload, sensations of bloating (0 to 10) and digestive well-being (-5 to + 5) were measured during 30-s. maneuvers alternating diaphragmatic contraction and diaphragmatic relaxation. Compared to diaphragmatic relaxation, diaphragmatic contraction was associated with diaphragmatic descent (by 21 + 3 mm; p < 0.001), objective abdominal distension (32 + 5 mm girth increase; p = 0.001), more intense sensation of bloating (7.3 + 0.4 vs. 8.0 + 0.4 score; p = 0.010) and lower digestive well-being (-0.9 + 0.5 vs. -1.9 + 0.5 score; p = 0.028). These results indicate that somatic postural tone underlying abdominal distention worsens the perception of visceral sensations (ClinicalTrials.gov ID: NCT04691882).

The effect of green kiwifruit on gas transit and tolerance in healthy humans

BACKGROUND

Green kiwifruit is a fiber-rich fruit that has been shown effective for treatment of constipation. However, fermentation of fibers by colonic bacteria may worsen commonly associated gas-related abdominal symptoms.

AIM

To determine the effect of green kiwifruit on transit and tolerance to intestinal gas in humans.

METHODS

In 11 healthy individuals, two gas challenge tests were performed (a) after 2 weeks on a low-flatulogenic diet and daily intake of 2 green kiwifruits and (b) after 2 weeks on a similar diet without intake of kiwifruits. The gas challenge test consisted in continuous infusion of a mixture of gases into the jejunum at 12 mL/min for 2 hours while measuring rectal gas evacuation, abdominal symptoms, and abdominal distension. During the 2 weeks prior to each gas challenge test (on-kiwifruit and off-kiwifruit), the number and consistency of stools, and abdominal symptoms were registered.

KEY RESULTS

Intake of kiwifruits was associated with more bowel movements per day (1.8 ± 0.1 vs 1.5 ± 0.1 off-kiwifruit; P = .001) and somewhat looser stools (Bristol score 3.3 ± 0.2 vs 2.8 ± 0.1 off-kiwifruit; P = .072) without relevant abdominal symptoms. Gas infusion produced similar gas evacuation (1238 ± 254 mL and 1172 ± 290 mL; P = .4355), perception of symptoms (score 1.2 ± 0.2 and 1.3 ± 0.3; P = .2367), and abdominal distension (17 ± 7 mm and 17 ± 6 mm; P = .4704) while on-kiwifruit or off-kiwifruit.

CONCLUSIONS AND INFERENCES

In healthy subjects, green kiwifruit increases stool frequency without relevant effects on intestinal gas transit and tolerance. If confirmed in patients, these fruits may provide a natural and well-tolerated treatment alternative for constipation.

The Effect of an Encapsulated Nutrient Mixture on Food Intake and Satiety: A Double-Blind Randomized Cross-Over Proof of Concept Study

Activation of the intestinal brake by infusing nutrients into the distal small intestine with catheters inhibits food intake and enhances satiety. Encapsulation of macronutrients, which protects against digestion in the proximal gastrointestinal tract, can be a non-invasive alternative to activate this brake. In this study, we investigate the effect of oral ingestion of an encapsulated casein and sucrose mixture (active) targeting the distal small intestine versus a control product designed to be released in the stomach on food intake, satiety, and plasma glucose concentrations. Fifty-nine volunteers received the active and control product on two separate test days. Food intake was determined during an ad libitum meal 90 min after ingestion of the test product. Visual analogue scale scores for satiety and blood samples for glucose analysis were collected at regular intervals. Ingestion of the active product decreased food intake compared to the control product (655 kcal compared with 699 kcal, respectively, p < 0.05). The area under the curve (AUC) for hunger was decreased (p < 0.05) and AUC for satiety was increased (p < 0.01) after ingestion of the active product compared to the control product. Ingestion of an encapsulated protein-carbohydrate mixture resulted in inhibition of food intake compared to a non-encapsulated control product.

Gastric gas dynamics in healthy humans

BACKGROUND

To cope with the daily increments of gastric gas, the stomach can propel gas to the small bowel or trigger the belching reflex. Our aim was to evaluate transit of free gastric gas in healthy humans, and its relationship with abdominal symptoms.

METHODS

In 24 healthy volunteers a gas mixture was infused into the stomach at 0 mL/min (sham infusion), 25 mL/min, 50 mL/min, and 100 mL/min (n = 6 each) up to 1500 mL. Belching, rectal gas evacuation, and abdominal perception were continuously recorded for 90 min.

KEY RESULTS

Sham infusion was associated to low rectal gas evacuation (187 ± 94 mL after 90 min), and belching (0 ± 0). In contrast, gastric gas infusion increased rectal gas evacuation (1198 ± 176 mL; P = .025) and belching (4 ± 1 belches; P = .0520) without differences between the infusion rates tested. Overall, there was a negative correlation between rectal gas evacuation and belching (r = -.72; P < .0001): 6 subjects had frequent belching (14 ± 2 belches) and minor rectal gas evacuation (330 ± 112 mL), whereas 12 subjects had virtually no belches (1 ± 1 belches) and greater rectal gas evacuation (1630 ± 147 mL; P < .001 vs belchers for both). Gas infusion induced lower abdominal symptoms in belchers (score increment 0.7 ± 0.3) than in rectal gas evacuators (score increment 1.7 ± 0.5; P = .033).

CONCLUSIONS AND INFERENCES

An excellent balance between belching and distal gastric empting allows the stomach to adapt to great variations in gas intake. In general, most gastric gas is emptied to distal intestinal segments, but in some circumstances gastric gas induces belching, a mechanism that may improve gas tolerance.

Utility of wireless motility capsule and lactulose breath testing in the evaluation of patients with chronic functional bloating

BACKGROUND

The precise aetiology of chronic bloating remains poorly understood and underlying gastroparesis, small bowel bacterial overgrowth and colonic inertia may, individually or collectively, play a role.

AIMS

In this retrospective cohort analysis of symptomatic patients with chronic persistent bloating, we determined the clinical utility of wireless motility capsule and lactulose breath test in further defining the underlying aetiology for functional bloating.

METHODS

Consecutive patients with chronic bloating underwent clinical assessment, wireless motility capsule testing and lactulose breath testing using standard protocols.

RESULTS

52 patients qualified for inclusion in this analysis, fulfilling Rome III criteria for functional bloating. Most patients (54%) had an abnormal wireless motility capsule study; of those, 11.5% had evidence of gastroparesis, 7.7% had small bowel transit delay, 15.8% had colonic inertia, 3.8% had delayed gastric and small bowel transit, 5.6% had combined gastric and colonic transit delay, 3.8% had delayed small bowel and colonic transit, and 5.6% had delayed gastric, small bowel and colon transit times. Using clinical questionnaires the median scores for bloating, constipation and eructation were not significantly different. Neither constipation nor eructation was specific to gastroparesis or colonic inertia but bloating was numerically more prevalent and severe in patients with delayed small bowel transit. 40% of patients had positive lactulose breath test but had no distinguishing clinical characteristics.

CONCLUSIONS

Chronic functional bloating may reflect underlying gastroparesis, small intestinal bacterial overgrowth or colonic inertia. Wireless motility capsule and lactulose breath test are useful in the assessment of patients with bloating and should be considered during evaluation.

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.

Bloating and distention in irritable bowel syndrome: the role of gas production and visceral sensation after lactose ingestion in a population with lactase deficiency

OBJECTIVES

Bloating and distention are often attributed to dietary factors by patients with irritable bowel syndrome (IBS). This study examined the effects of gas production and visceral hypersensitivity on digestive symptoms after lactose ingestion in a population with lactase deficiency.

METHODS

IBS patients (n=277) and healthy controls (HCs, n=64) underwent a 20-g lactose hydrogen breath test (LHBT) with evaluation of hydrogen gas production and lactose intolerance (LI) symptoms. Abdominal distention (199 IBS, 40 HCs) was measured during LHBT. Rectal sensitivity (74 IBS, 64 HCs) was assessed by barostat studies.

RESULTS

Hydrogen production and distention were similar in IBS patients and HCs during LHBT; however, LI was more frequent in IBS (53.8 vs. 28.1%, P<0.001), especially bloating (39.0% vs. 14.1%, P<0.001) and borborygmi (39.0 vs. 21.9%, P=0.010). Only 59.0% of patients with bloating had distention. No correlation was observed between girth increment and bloating (P=0.585). IBS patients had lower rectal sensory thresholds (P=0.001). Multivariate analysis indicated that hydrogen production increased bloating (odds ratio (OR) 2.19, 95% confidence interval (CI) 1.09-4.39, P=0.028) and borborygmi (OR 12.37, 95% CI 3.34-45.83, P<0.001) but not distention (P=0.673). Visceral hypersensitivity was associated with bloating (OR 6.61, 95% CI 1.75-25.00, P=0.005) and total symptom score (OR 3.78, 95% CI 1.30-10.99, P=0.014).

CONCLUSIONS

Gas production and visceral hypersensitivity both contribute to digestive symptoms, especially bloating and borborygmi, in IBS patients after lactose ingestion. Objective abdominal distention is not correlated with subjective bloating.

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.

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.

Pathophysiology, evaluation, and treatment of bloating: hope, hype, or hot air?

Abdominal bloating is commonly reported by men and women of all ages. Bloating occurs in nearly all patients with irritable bowel syndrome, and it also occurs in patients with other functional and organic disorders. Bloating is frequently disturbing to patients and frustrating to clinicians, as effective treatments are limited and are not universally successful. Although the terms bloating and abdominal distention are often used interchangeably, these symptoms likely involve different pathophysiologic processes, both of which are still not completely understood. The goal of this paper is to review the pathophysiology, evaluation, and treatment of bloating and abdominal distention.

Bloating in constipation: relevance of intraluminal gas handling

The symptom of bloating and sometimes associated increase in abdominal girth (distension) is often described by patients as very intrusive, significantly impacting their quality of life. Indeed many patients rank it as their most bothersome symptom, even above abdominal pain. Despite this fewer patients appear to seek medical attention for this problem compared with other gastrointestinal symptoms. This has been attributed to the fact that most sufferers usually have other symptoms, such as abdominal pain, which they may perceive as potentially more serious, and hence seek preferential medical advice and treatment. This review aims to clarify the meaning of the terms bloating and distension, explores their association with constipation, and discusses possible pathophysiologies, in particular the relevance of intraluminal gas handling.

[Abdominal bloating: an up-to-date]

Bloating is a common symptom, especially in women. In the clinical practice, it remains a therapeutic challenge. Since recently, its pathophysiology is better understood: an impaired transit of gas (particularly in the small bowel) or a visceral hypersensitivity leading to the induction of an abdominal discomfort despite a normal volume of gas are two of the main causes, far more frequent than an excessive production of gas. Moreover, bloating can be related to abnormal viscera-somatic reflexes promoting both an abdomino-phrenic dyssynergia and the relaxation of the muscles of the abdominal wall. From a therapeutic point of view, the efficacy of the gas absorbants remains to be more documented. Besides the treatment of a constipation and the avoidance of nutrients either highly fermentable or rich in fructose, other therapeutic options include prokinetics and drugs acting on visceral sensitivity. Probiotics are another promising option. In some centers, a non pharmacological therapeutic approach, mainly based on hypnosis, is discussed.

Abdominal accommodation: a coordinated adaptation of the abdominal wall to its content

BACKGROUND AND AIM

We previously showed that colonic gas infusion increases the girth and modifies the muscular activity of the anterior abdominal wall. We hypothesized that abdominal accommodation to volume loads is an active process instrumented by the coordinated activity of the anterior wall and the diaphragm.

METHODS

To increase intraabdominal volume in healthy subjects, a gas was infused into the colon (1.44 L in 1 h) while measuring girth (by tape measure) and electromyography (EMG) activity of the anterior wall (via four pairs of surface electrodes) and the diaphragm (via six ring electrodes over an esophageal tube in the hiatus). After preliminary feasibility studies (N = 12), postural activity (N = 6) and responses to colonic gas loads, both with the trunk erect (N = 8) and in supine position (N = 8), were studied. A morphometric analysis was performed by computed tomography, image analysis (N = 8).

RESULTS

In the erect position, anterior wall tone was higher and diaphragmatic tone was lower than in the supine position. With the trunk erect, gas infusion induced diaphragmatic relaxation (by 21 +/- 3%; P < 0.05) and anterior wall contraction (16 +/- 4% EMG increment; P < 0.05). By contrast, in the supine position, it induced diaphragmatic contraction (15 +/- 6%, P < 0.05), while the anterior wall, in the absence of postural tone, showed no change (3 +/- 2%, NS). Gas infusion was associated with girth increase (7.3 +/- 1.0 mm with the trunk erect and 8.6 +/- 1.4 mm in the supine position) and diaphragmatic ascent (17.6 +/- 5.2 mm; P < 0.05).

CONCLUSION

The degree of abdominal distension produced by intraabdominal volume increments results from posture-related abdomino-phrenic muscular responses.

Intestinal gas retention in patients with idiopathic slow-transit constipation

Patients with slow-transit constipation (STC) have delayed colonic transit for solid und liquid bowel contents but intestinal gas handling has not been studied so far. Different nutrients influence motor and sensory gut function. We hypothesized that, in patients with STC, alteration of regulatory mechanisms may result in impaired intestinal gas dynamics. On 3 separate days, validated gas challenge was performed in 10 STC patients and 10 volunteers during duodenal saline, lipids, or intravenous glucose. During saline only 60% +/- 8% of gas was cleared by STC patients after 60-min gas infusion, vs. 91% +/- 2% by controls (P < 0.001). Acute hyperglycemia or lipids did not change intestinal gas dynamics in these patients (saline infusion), but compared to healthy subjects, significant intestinal gas retention occurred. In STC, disturbances of intestinal gas dynamics include basal intestinal gas retention, and this is virtually not affected by acute hyperglycemia or duodenal lipids.

Irritable bowel syndrome and bloating

Gaseous symptoms in irritable bowel syndrome (IBS) including eructation, flatulence, and bloating occur as a consequence of excess gas production, altered gas transit, abnormal perception of normal amounts of gas within the gastrointestinal tract, or dysfunctional somatic muscle activity in the abdominal wall. Because of the prominence of gaseous complaints in IBS, recent investigations have focussed on new insights into pathogenesis and novel therapies of bloating. The evaluation of the IBS patient with unexplained gas and bloating relies on careful exclusion of organic disease with further characterisation of the underlying condition with directed functional testing. Treatment of gaseous symptomatology in IBS should be targeted to pathophysiologic defects whenever possible. Available therapies include lifestyle alterations, dietary modifications, enzyme preparations, adsorbents and agents which reduce surface tension, treatments that alter gut flora, and drugs that modulate gut transit.

Gas distribution within the human gut: effect of meals

BACKGROUND AND AIMS

Patients frequently complain of gas symptoms precipitated by meals, but the effect of early digestion on intestinal gas content remains unknown. Our aim was to determine the influence of meals on intestinal gas volume and distribution.

METHODS

First, we developed a CT image analysis program, based on independent software modules, to measure gas content within the gut. The system was validated in nine healthy subjects by taking helical abdominal CT scans before and after rectal infusion of known volumes of air (100-400 mL). In 15 healthy subjects, intestinal gas distribution was measured in fast and early postcibal CT scans. The postcibal scan was taken 99 +/- 22 minutes after a 597 +/- 57 kcal meal.

RESULTS

The volume of gas infused per rectum was detected with an accuracy of 100.4 +/- 3.0%. During fasting, intestinal gas volume was 94 +/- 7 mL (excluding two extreme outliers). After the meal, gas content within the gut increased by 64.7% (up to 149 +/- 21 mL, P < 0.01 vs fast) and the increment occurred in the colon (59 +/- 9 mL precibal vs 121 +/- 20 mL postcibal, P < 0.001), while other gut compartments remained unchanged.

CONCLUSION

Ingestion of a meal activated gas metabolism and increased gas content within the gut. The increment occurred early, presumably prior to colonic fermentation of food substrates and was localized in the distal gut, suggesting that gas had a proximal origin and was propelled caudally.

Mechanisms of hypersensitivity in IBS and functional disorders

General introduction The concept of visceral hypersensitivity is accepted as being germane to several functional gastrointestinal disorders (FGIDs). The causes or risk factors associated with this hypersensitivity are unclear. This article addresses the proposed mechanisms leading to hypersensitivity: from genetic to inflammatory disorders, from central to peripheral alterations of function. However, in order to place visceral hypersensitivity in a more global perspective as an aetiological factor for FGIDs, it also provides a review of recent evidence regarding the role of other peripheral mechanisms (the intraluminal milieu), as also genetic factors in the pathophysiology of these disorders. The article has been divided into five independent sections. The first three sections summarize the evidence of visceral hypersensitivity as a biological marker of functional gut disorders, the peripheral and central mechanisms involved, and the role of inflammation on hypersensitivity. In opposition to visceral hypersensitivity as an isolated phenomenon in functional gut disorders, the last two sections focus on the importance of peripheral mechanisms, like motor disturbances, specifically those resulting on altered transport of intestinal gas, and alterations of the intraluminal milieu and genetics.

Relationship of abdominal bloating to distention in irritable bowel syndrome and effect of bowel habit

BACKGROUND & AIMS

The relationship between the sensation of bloating, often ranked as the most bothersome symptom by patients with irritable bowel syndrome (IBS), and actual distention manifest as an increase in abdominal girth is controversial. Investigation of this problem has been hampered by the lack of a reliable ambulatory technique to measure abdominal girth. The aim of this study was to use the technique of abdominal inductance plethysmography to compare diurnal variation in girth in IBS patients and healthy volunteers, relating these changes to the sensation of bloating.

METHODS

Abdominal girth was recorded for 24 hours in 20 IBS-constipation (age, 18-73 y), 20 IBS-diarrhea (age, 25-62 y) and 10 IBS-alternating (age, 21-59 y) female patients meeting Rome II criteria and 20 healthy female controls (age, 18-67 y). All subjects pursued normal daily activities, recording their symptoms of bloating and pain together with bowel habit.

RESULTS

All patients with IBS, irrespective of bowel habit, reported significantly greater bloating than controls (P < .0001). Forty-eight percent of patients also showed distention beyond the 90% control range, with this being most prominent in IBS-constipation. Bloating correlated strongly only with distention in IBS-constipation (r > or = 0.48; P < or = .02). Neither bloating nor distention in IBS was related to body mass index, age, parity, or psychologic status.

CONCLUSIONS

Abdominal distention is a clearly definable phenomenon in IBS that can reach 12 cm. However, it only occurs in half of patients reporting bloating, and the 2 only correlate in IBS-constipation. Bloating and distention may differ pathophysiologically and this appears to be reflected in the bowel habit subtype.

Intestinal tone and gas motion

The intestine propels and evacuates large gas loads without detectable phasic contractions by manometry. We hypothesized that intestinal gas motion is produced by changes in gut tone and capacitance. In 13 healthy subjects, changes in duodenal tone were measured by a barostat during continuous perfusion of lipids (Intralipid, 1 kcal min(-1)) into the duodenum for 60 min. In separate groups, the effects of jejunal gas infusion (N2, CO2 and O2 in venous proportions at 12 mL min(-1) starting after 15 min lipid perfusion) and sham infusion were tested. Gas outflow was collected continuously via an intrarectal cannula. Duodenal lipid perfusion produced a rapid duodenal relaxation (volume increased by 48 +/- 18%; P < 0.01 vs basal). Gas infusion increased gas evacuation (184 +/- 59 mL), and this was associated with a tonic contraction of the duodenum (R = 0.86; P < 0.01) that completely reverted the lipid-induced duodenal relaxation (volume decreased by 42 +/- 13%; P < 0.05). During sham infusion only 52 +/- 28 mL of gas were evacuated (P < 0.05 vs gas infusion), and the duodenum remained relaxed due to the effect of lipids (0 +/- 1% volume reduction; ns). In conclusion, intestinal gas propulsion and clearance is associated with a tonic contraction of the gut wall and reduced gut capacitance.

Impaired small bowel gas propulsion in patients with bloating during intestinal lipid infusion

OBJECTIVE

In healthy individuals, intraluminal lipids delay intestinal gas clearance, and this reflex is exaggerated in patients with irritable bowel syndrome (IBS). Our aim was to determine the site of action of abnormal lipid-induced reflexes in IBS.

METHODS

In six patients with (IBS) predominantly complaining of bloating and in six healthy subjects, a mixture of gas (N2, O2, and CO2 in venous proportions to minimize diffusion) was infused (12 mL/min) either into the jejunum or into the ileum for 2 h, with simultaneous perfusion of lipids (0.5 kcal/min) into the proximal duodenum. Rectal gas evacuation was measured by a barostat. Abdominal perception (by a 0-6 scale) and girth changes were measured at 15-min intervals. The effects of jejunal versus ileal gas infusion were compared by paired tests in random order on separate days.

RESULTS

IBS patients exhibited significant gas retention during infusion of gas into the jejunum (398 +/- 90 mL vs-210 +/- 105 mL in health, p < 0.05) but not during ileal infusion (-79 +/- 87 mL vs-79 +/- 78 mL in health, NS; p < 0.05 vs jejunal infusion). Gas retention during jejunal gas infusion in IBS patients was associated with significant abdominal distension (11 +/- 3 mm girth increment vs 0 +/- 1 mm during ileal gas infusion and 1 +/- 1 mm in health, p < 0.05 for both) and abdominal symptoms (3.6 +/- 0.6 score vs 2.6 +/- 0.7 score during ileal gas infusion and 1.6 +/- 0.5 score in health, p < 0.05 for both).

CONCLUSIONS

In IBS patients intraluminal lipids impair intestinal gas clearance because of upregulated reflex inhibition of small bowel transit, without appreciable colonic effects.

Duodenal infusion of different nutrients and the site of gaseous stimulation influence intestinal gas dynamics

OBJECTIVE

Excessive intestinal gas can be involved in postprandial abdominal symptom generation, but whether the small bowel influences intestinal gas dynamics, depending on the ingested meal, remains to be demonstrated. We compare the intestinal response to a proximal and distal small intestinal gas challenge during different duodenal nutrient components.

MATERIAL AND METHODS

We randomly studied 32 healthy subjects, twice, on different days with a gas mixture infused at 12 ml/min either directly into the proximal jejunum or into the ileum; during duodenal lipids, amino acids, glucose, at 1 kcal/min each, or saline (n=8 for each group). Gas evacuation was monitored continuously and abdominal perception and girth changes were assessed.

RESULTS

In response to the jejunal gas challenge, duodenal lipids delayed intestinal gas clearance more potently than amino acids (733+/-26 ml and 541+/-108 ml final gas retention; p<0.001), but when gas was directly infused into the ileum the retained volumes were much smaller (271+/-78 ml and 96+/-51 ml; p<0.001). During duodenal glucose, intestinal gas clearance following jejunal or ileal gas infusion was not significantly influenced. Abdominal perception in response to the jejunal and ileal gas challenge only increased slightly during duodenal lipids (2.0+/-0.3 score and 2.3+/-0.6 score; p<0.05 versus control).

CONCLUSION

Postprandial intestinal gas clearance is hampered by duodenal lipids and amino acids but not by glucose. Specific inhibitory effects are more pronounced when gas is infused into the jejunum, which underlines the importance of the small intestine in postprandial gas retention.

Effect of high- and low-caloric mixed liquid meals on intestinal gas dynamics

High-caloric meals can evoke postprandial abdominal complaints involving disturbances in intestinal gas balance. We aimed to determine the influence of the caloric content of meals on intestinal gas dynamics. Eight healthy subjects (five women, three men; age range, 25-43 years) underwent paired studies with low (1 kcal/min)- and high (3 kcal/min)-caloric meal infusion 35% fat, (45% carbohydrate, 20% protein) into the duodenum in random order and proximal jejunal gas infusion. Gas evacuation, perception, and abdominal girth were assessed. The low-caloric meal caused neither gas retention (-7 +/- 58 ml) nor girth changes (0 +/- 0 mm). In contrast, the high-caloric meal led to significant gas retention (705 +/- 56 ml) and increased abdominal perimeter (7 +/- 1 mm; P < 0.001 vs. the low-caloric meal for both). Thus, a high caloric load of nutrients arriving at the duodenum modulates both intestinal gas transit and abdominal perimeter.

New insights into the pathophysiology of irritable bowel syndrome: implications for future treatments

Irritable bowel syndrome (IBS) is a multifactorial disorder characterized by abdominal pain and altered bowel habits. Chronic symptoms may occur due to changes in gastrointestinal motor function, enhanced perception of gut stimuli, and psychosocial factors. Recent data suggest that abnormal processing of afferent signals occurs in IBS patients. A newly recognized causative factor in a subset of IBS patients is post-infectious IBS. Altered transport of intestinal gas and bowel distention may contribute to abdominal discomfort, pain, and bloating. Changes in gut microflora have also been reported, but data remain scant. Advances have been made in our understanding of serotonin signaling and metabolism in IBS patients, in part due to the introduction of specific receptor agonists and antagonists. Finally, exciting data are emerging on genetic alterations that may contribute to the pathophysiology and treatment of IBS. Increasingly novel mechanisms are being identified that should aid in better understanding of the complex pathophysiology of IBS and developing new therapies.

Abdominal bloating

Abdominal bloating is a common and significant clinical problem that remains to be scientifically addressed. Bloating is one of the most bothersome complaints in patients with various functional gut disorders. However, in the current standard classification, abdominal bloating is merely regarded as a secondary descriptor, which masks its real clinical effect. Four factors are involved in the pathophysiology of bloating: a subjective sensation of abdominal bloating, objective abdominal distention, volume of intra-abdominal contents, and muscular activity of the abdominal wall. The primer to elicit subjective bloating may be any of the other 3 factors, or the sensation may be related to distorted perception. All of these mechanisms may play an independent role or may be interrelated. Gas transit studies have evidenced that patients with bloating have impaired reflex control of gut handling of contents. Segmental pooling, either of gas or of solid/liquid components, may induce a bloating sensation, particularly in patients with altered gut perception. Furthermore, altered viscerosomatic reflexes may contribute to abdominal wall protrusion and objective distention, even without major intra-abdominal volume increment. Bloating probably is a heterogeneous condition produced by a combination of pathophysiological mechanisms that differ among individual patients and that in most cases are subtle and undetectable by conventional methods. Further advances in the pathophysiology and clinical forms of bloating are warranted to develop mechanistic strategies rather than the current empiric treatment strategies for comprehensive and effective management of this problem.

Bloating and intestinal gas

The most common symptoms associated with intestinal gas are eructation, flatulence, abdominal bloating, and distention. Aerophagia is an uncommon cause of eructation in which repetitive air swallowing results in belching, abdominal distention, and increased flatus. Few therapies have been shown to be effective in treating these symptoms. Eructation can be treated by decreasing excessive air swallowing. Occasionally, behavioral therapy and psychotherapy are employed. Bloating, distention, and other gas-related symptoms are common in functional gastrointestinal disorders; however, their pathophysiology is poorly understood. Additionally, evidence supporting the use of various available therapies in treating gas-related symptoms is either absent or poor. Dietary therapy may be effective in patients with excessive gas production. Excessive gas production, identified by increased flatus, may benefit from a low-carbohydrate diet. Many patients with gas-related symptoms have normal gas production but may have either impaired gas transport or transit through the gut or visceral hypersensitivity. Few studies have addressed the treatment of impaired gas transport.

Towards a better understanding of abdominal bloating and distension in functional gastrointestinal disorders

Abdominal bloating is an extremely common symptom affecting up to 96% of patients with functional gastrointestinal disorders and even 30% of the general population. To date bloating has often been viewed as being synonymous with an actual increase in abdominal girth, but recent evidence suggests that this is not necessarily the case. This review examines the relationship between the symptom of bloating and the physical sign of abdominal distension, as well as examining the epidemiology, pathophysiology and treatment options available for this debilitating aspect of the functional gastrointestinal disorders. Pathophysiological mechanisms explored include psychological factors, intestinal gas accumulation, fluid retention, food intolerance and malabsorption of sugars, weakness of abdominal musculature, and altered sensorimotor function. Treatment options are currently rather limited but include dietary changes, pharmacological approaches, probiotics and hypnotherapy.

Origin of gas retention and symptoms in patients with bloating

BACKGROUND & AIMS

Patients reporting abdominal bloating exhibit impaired tolerance to intestinal gas loads. The aim of this study was to identify the gut compartment responsible for gas retention.

METHODS

In 30 patients predominantly reporting abdominal bloating (24 with irritable bowel syndrome and 6 with functional bloating) and 22 healthy subjects, gas (nitrogen, carbon dioxide, and oxygen) was infused into the intestine for 2 hours while measuring rectal gas outflow. First, in 12 patients and 10 healthy subjects, gas transit (24 mL/min jejunal infusion labeled with 74 MBq bolus of 133 Xe) was measured by scintigraphy. Second, in groups of patients and healthy subjects, the effects of gas infusion (12 mL/min) in the jejunum versus ileum, jejunum versus cecum, and jejunum versus sham infusion (n=6 each) were compared by paired tests.

RESULTS

In patients, total gut transit of gas was delayed (50% clearance time, 33 +/- 4 min vs 23 +/- 4 min in healthy subjects; P <.05) owing to impaired small bowel transit (50% clearance time, 20 +/- 2 min vs 12 +/- 3 min in healthy subjects; P <.05), whereas colonic transit was normal (50% clearance time, 13 +/- 2 min vs 11 +/- 2 min in healthy subjects; not significant). Furthermore, jejunal gas infusion in patients was associated with gas retention (329 +/- 81 mL vs 88 +/- 79 mL in healthy subjects; P <.05), whereas direct ileal or colonic infusion was not (61 +/- 103 mL and -143 +/- 87 mL retention, respectively).

CONCLUSIONS

In patients reporting bloating, the small bowel is the gut region responsible for ineffective gas propulsion.

Small intestinal motility

PURPOSE OF REVIEW

To review recently published studies presenting novel and relevant information on small intestinal motility in humans and animals.

RECENT FINDINGS

The reviewed studies covered a variety of topics with several themes emerging. The relation between bacterial overgrowth and altered intestinal motility gathers support in a variety of conditions including portal hypertension and senescence. The mechanisms of postoperative ileus are becoming better understood. Cannabinoids play an important role in ileus and this further highlights the importance of these compounds in intestinal motility. Luminal impedance appears to be an important tool for investigation of intestinal flow.

SUMMARY

Small intestinal motility remains an understudied area. Recent publications have shed additional light on myogenic, neural, and hormonal control mechanisms. Novel investigative techniques will likely further improve our understanding.

Treatment of Excessive Intestinal Gas

Symptoms of excessive intestinal gas may be related to eructation, excessive or odoriferous gas evacuation, and/or abdominal symptom attributed to gas retention. Patients with aerophagia and excessive eructation can be usually retrained to control air swallowing, but if present, basal dyspeptic symptoms may remain. Patients with excessive or odoriferous gas evacuation may benefit from a low-flatulogenic diet. In patients with gas retention due to impaired anal evacuation, anal incoordination can be resolved by biofeedback treatment, which also improves fecal retention, and thereby reduces the time for fermentation. Other patients complaining of abdominal symptoms that they attribute to intestinal gas, probably have irritable bowel syndrome or functional bloating, and their treatment options specifically targeting gas-related symptoms basically include prokinetics and spasmolytics. There is no consistent evidence to support the use of gas-reducing substances, such as charcoal or simethicone.