Optimizing analysis of stable isotope breath tests to estimate gastric emptying of solids

Ten controversies in gastroparesis and a look to the future

BACKGROUND

Gastroparesis is a complex, challenging gastrointestinal disorder presenting with upper gastrointestinal symptoms, especially nausea and vomiting, with significant impact on patients' quality of life. After ruling out mechanical obstruction, it is essential to identify delay in gastric emptying for definitive diagnosis. The most common causes are idiopathic (no identified etiology), diabetes mellitus, and postsurgical status. Management of gastroparesis focuses on dietary modifications and treatment directed to symptom relief. Unfortunately, approximately one-third of patients are refractory to pharmacological therapy, and the effectiveness of the few nonpharmacological options has been questioned.

PURPOSE

Extensive review of the literature identifies several uncertainties or controversies regarding the differential diagnosis based on the spectrum of symptoms, the lack of availability of reliable diagnostic test, and questions regarding effective therapeutic options. In this review, we discuss ten controversies regarding gastroparesis: clinical presentation, diagnosis, overlap syndromes, pathophysiology, etiology, as well as pharmacological and nonpharmacological therapeutic options. In addition, we briefly review studies exploring pathological, inflammatory, and molecular disturbances affecting the intrinsic neuromuscular elements that may be involved in the pathophysiology of gastroparesis and may constitute possible therapeutic targets in the future. Finally, we tabulate future research opportunities to resolve these controversies in the management of patients with gastroparesis.

Impact of preoperative oral domperidone on gastric residual volume after clear fluid ingestion in patients scheduled for elective surgery: a randomized controlled trial

INTRODUCTION

Oral domperidone is a prokinetic drug that enhances gastric emptying, which has a positive effect in decreasing gastric residual volume (GRV), subsequently decreasing the risk of pulmonary aspiration. This study aimed to assess the effect of preoperative oral domperidone on gastric residual volume, detected by ultrasound for patients undergoing elective surgery under general anesthesia.

MATERIAL AND METHODS

This randomized double-blinded controlled placebo trial was conducted in 40 patients who were randomly assigned to two equal groups: the domperidone group (D) ( n = 20): patients received 400 mL of apple juice as a clear fluid, two hours preoperatively, and an oral domperidone 10 mg tablet; and the placebo group (P) ( n = 20): patients received 400 mL of apple juice as a clear fluid two hours preoperatively with a placebo tablet. Gastric residual volume detected by ultrasound was the primary outcome and postoperative nausea and vomiting (PONV) was the secondary outcome.

RESULTS

There was no statistically significant difference in the mean gastric residual volume detected by ultrasound between groups after 1 hour ( P > 0.05). However, the mean gastric residual volume detected by ultrasound after 2 hours was statistically significantly lower with domperidone (55.95 ± 6.72 mL) than with the placebo group (70.22 ± 13.00 mL) ( P < 0.05). There was no statistically significant difference between groups regarding PONV, with a P -value > 0.05.

CONCLUSIONS

Preoperative oral domperidone intake was effective in decreasing the GRV measured by ultrasound.

Measurement of Gastric Emptying Using a 13C-octanoic Acid Breath Test with Wagner-Nelson Analysis and Scintigraphy in Type 2 Diabetes

INTRODUCTION

Breath tests utilising ¹³C-labelled substrates for the assessment of gastric emptying have been applied widely. Wagner-Nelson analysis is a pharmacokinetic model that can be utilised to generate a gastric emptying curve from the % ¹³CO₂ measured in breath samples. We compared Wagner-Nelson analysis with (i) scintigraphy and (ii) conventional breath test modelling to quantify gastric emptying in type 2 diabetes.

METHODS

Thirteen patients (age 68.1±1.5 years, body mass index 31.0±0.9 kg/m², HbA1c 6.3±0.2%) consumed a mashed potato meal comprising 65 g powdered potato, 20 g glucose, 250 ml water, an egg yolk labelled with 100 μL ¹³C-octanoic acid and 20MBq ^99mTc-calcium phytate. Scintigraphic data were acquired and breath samples collected for 4 hours after the meal. Gastric emptying curves were derived based on each technique; the 50% emptying time and intragastric retention at 60 min were also calculated.

RESULTS

With Wagner-Nelson analysis, a K_el=0.60 (the elimination constant) best approximated the scintigraphic gastric emptying curve. There was a relationship between the T50 calculated with scintigraphy and by both Wagner-Nelson K_el=0.60 (r²=0.45, P<0.05) and conventional analysis (r²=0.44, P<0.05). There was no significant difference in the 50% gastric emptying time for scintigraphy (68.5±4.8 min) and Wagner-Nelson K_el=0.60 (71.3±4.5 min), however, the 50% gastric emptying time calculated by conventional analysis was much greater at 164.7±6.0 min (P<0.001).

CONCLUSION

In type 2 diabetes, gastric emptying of a mashed potato meal measured using a ¹³C-octanoic acid breath test analysed with Wagner-Nelson K_el=0.60 closely reflects measurements obtained with scintigraphy, whereas, in absolute terms, the conventional breath test analysis does not.

Gastroparesis in pregnancy

Gastroparesis is a functional gastrointestinal disorder that more commonly affects women, with most cases being diagnosed during childbearing age. However, there is a paucity of data and guidelines to specifically highlight the epidemiology, disease course, maternal and fetal impact, and the management of existing gastroparesis during pregnancy. Apart from metoclopramide, there is no approved therapy specifically indicated for gastroparesis. More importantly, pregnant and breastfeeding women are excluded from clinical trials evaluating pharmacologic agents in the management of gastroparesis. This poses a real challenge to healthcare providers in counseling and managing patients with gastroparesis. In this systematic review, we summarize the current available literature and the knowledge gaps in the impact of pregnancy on gastroparesis and vice versa. We also highlight the efficacy and safety profiles of available pharmacologic and nonpharmacologic therapies in the management of patients with gastroparesis, with emphasis on judicious use of dietary approaches that are deemed relatively safe during pregnancy.

The [13 C]octanoic acid breath test for gastric emptying quantification: A focus on nutrition and modeling

Gastric emptying (GE) is the process of food being processed by the stomach and delivered to the small intestine where nutrients such as lipids are absorbed into the blood circulation. The combination of an easy and inexpensive method to measure GE such as the CO₂ breath test using the stable isotope [¹³C]octanoic acid with semi‐mechanistic modeling could foster a wider application in nutritional studies to further understand the metabolic response to food. Here, we discuss the use of the [¹³C]octanoic acid breath test to label the solid phase of a meal, and the factors that influence GE to support mechanistic studies. Furthermore, we give an overview of existing mathematical models for the interpretation of the breath test data and how much nutritional studies could benefit from a physiological based pharmacokinetic model approach.

Gastric digestion of cow milk, almond milk and oat milk in rats

In this study, gastric digestion of isocaloric and iso-macronutrient cow milk, almond milk and oat milk were compared in rats euthanized at different post-feeding times.

Evaluation of gastric emptying in patients with gastroparesis by three-dimensional ultrasound

Background

To diagnose gastroparesis, it is necessary to assess gastric emptying accurately. This study aims to investigate the role of three-dimensional ultrasonography (3-D US) on the measurement of gastric volume to evaluate gastric accommodation in healthy patients.

Methods

In this study, 21 volunteers, 46 patients with diabetic gastroparesis (DG), and 22 patients with postsurgical gastroparesis (PSG) underwent 3-D US after oral administration of 250 mL gastrointestinal contrast at 2, 30, 60, and 90 min. The volume of the contrast agent in the stomach was then calculated using the virtual organ computer-aided analysis (VOCAL) (Virtual Organ Computer-aided AnaLysis, General Electric Medical Systems, Kretztechnik, Zipf, Austria).

Results

In the DG group, the gastric residue volumes at postprandial 60 and 90 min were significantly higher than those in the healthy group (P<0.05), and the areas under the receiver operating characteristic (ROC) curve of these parameters were 0.830 and 0.957, respectively. There were significant differences between the PSG and healthy groups at 60 and 90 min; however, the AUC of gastric residue at 90 min (0.955) was higher than the AUC at 60 min (0.697).

Conclusions

Therefore, this study showed that the 3-D US is a powerful tool for assessing gastric emptying and provides a new strategy for diagnosing gastroparesis.

A population pharmacokinetic-pharmacodynamic model of YH12852, a highly selective 5-hydroxytryptamine 4 receptor agonist, in healthy subjects and patients with functional constipation

YH12852, a novel, highly selective 5-hydroxytryptamine 4 (5-HT4 ) receptor agonist, is currently under development to treat patients with functional constipation. In this study, we aimed to develop a pharmacokinetic (PK)-pharmacodynamic (PD) model that adequately described the time courses of the plasma concentrations of YH12852 and its prokinetic effect as assessed by the Gastric Emptying Breath Test (GEBT) and to predict the prokinetic effect of YH12852 at higher doses through PD simulation. We used the plasma concentrations of YH12852 from patients with functional constipation and healthy subjects and the GEBT results from healthy subjects obtained from a phase I/IIa trial. The PK-PD modeling and covariate analysis were performed using NONMEM software. The prokinetic effect of YH12852 was described using a semimechanistic multicompartment PD model and an empirical model by Ghoos et al. A two-compartment model with first-order absorption adequately described the observed concentration-time profiles of YH12852. The semimechanistic multicompartment PD model and the revised Ghoos model with two slope parameters adequately described the observed kPCDt (the percent dose of 13 C excreted in the exhaled air at minute t after completing the test meal, multiplied by 1000) values. YH12852 accelerated gastric emptying even at low doses of 0.05-0.1 mg, and its prokinetic effect was greater in subjects suffering from more severe functional constipation. The PD simulation experiments revealed that the change from baseline in the half time for gastric emptying induced by YH12852 increased in a dose-dependent manner at 0.05-5 mg although the results at doses >0.1 mg were extrapolated. We also showed that the empirical Ghoos model is a special case of the general semimechanistic multicompartment PD model for gastric emptying.

European guideline on indications, performance and clinical impact of 13 C-breath tests in adult and pediatric patients: An EAGEN, ESNM, and ESPGHAN consensus, supported by EPC

Introduction

¹³C‐breath tests are valuable, noninvasive diagnostic tests that can be widely applied for the assessment of gastroenterological symptoms and diseases. Currently, the potential of these tests is compromised by a lack of standardization regarding performance and interpretation among expert centers.

Methods

This consensus‐based clinical practice guideline defines the clinical indications, performance, and interpretation of ¹³C‐breath tests in adult and pediatric patients. A balance between scientific evidence and clinical experience was achieved by a Delphi consensus that involved 43 experts from 18 European countries. Consensus on individual statements and recommendations was established if ≥ 80% of reviewers agreed and <10% disagreed.

Results

The guideline gives an overview over general methodology of ¹³C‐breath testing and provides recommendations for the use of ¹³C‐breath tests to diagnose Helicobacter pylori infection, measure gastric emptying time, and monitor pancreatic exocrine and liver function in adult and pediatric patients. Other potential applications of ¹³C‐breath testing are summarized briefly. The recommendations specifically detail when and how individual ¹³C‐breath tests should be performed including examples for well‐established test protocols, patient preparation, and reporting of test results.

Conclusion

This clinical practice guideline should improve pan‐European harmonization of diagnostic approaches to symptoms and disorders, which are very common in specialist and primary care gastroenterology practice, both in adult and pediatric patients. In addition, this guideline identifies areas of future clinical research involving the use of ¹³C‐breath tests.

Spirulina breath test indicates differences in gastric emptying based on age, gender, and BMI

BACKGROUND

Measurements of gastric emptying (GE) by scintigraphy in the pediatric population are based on adult standards. Due to radiation exposure, scintigraphy cannot be performed on healthy children to establish norms of GE in the pediatric population. Stable isotope breath tests (GEBTs) pose no such health risk to children. This study sought to determine the feasibility of a GEBT in children and to investigate whether GE may differ by age, gender, or body mass index (BMI).

METHODS

Fifty healthy children 6 to 18 years underwent a ¹³ C-Spirulina platensis GEBT. Breath samples were obtained at baseline, every 15 min for 1 h, and at 30-min intervals for 3 h thereafter. Seventeen similarly aged patients with dyspeptic symptoms concurrently underwent scintigraphy and the GEBT.

KEY RESULTS

Forty-six healthy subjects were included in the final analysis. Females had an overall slower rate of GE than did males. At nearly all timepoints, children with a BMI >85^th percentile had slower GE than normally weighted children. The GE rate of children aged 6-9 reached a maximum later than did the rate of older children. Thirteen patients undergoing scintigraphy were included in the comparative analysis. The agreement between scintigraphic and GEBT half-times as measured by the concordance correlation coefficient was 0.383 (95% CI: 0.02-0.65).

CONCLUSIONS AND INFERENCES

GEBT was easily accomplished in healthy children. Differences of GE rates by age, gender, and BMI support the need for establishing pediatric standards of GE. One way to establish such standards may be through the use of a GEBT.

Effects of GLP-1 and Its Analogs on Gastric Physiology in Diabetes Mellitus and Obesity

The processing of proglucagon in intestinal L cells results in the formation of glucagon, GLP-1, and GLP-2. The GLP-1 molecule becomes active through the effect of proconvertase 1, and it is inactivated by dipeptidyl peptidase IV (DPP-IV), so that the half-life of endogenous GLP-1 is 2-3 min. GLP-1 stimulates insulin secretion from β cells in the islets of Langerhans. Human studies show that infusion of GLP-1 results in slowing of gastric emptying and increased fasting and postprandial gastric volumes. Retardation of gastric emptying reduces postprandial glycemia. Exendin-4 is a peptide agonist of the GLP-1 receptor that promotes insulin secretion. Chemical modifications of exendin-4 and GLP-1 molecules have been accomplished to prolong the half-life of GLP-1 agonists or analogs. This chapter reviews the effects of GLP-1-related drugs used in treatment of diabetes or obesity on gastric motor functions, chiefly gastric emptying. The literature shows that diverse methods have been used to measure effects of the GLP-1-related drugs on gastric emptying, with most studies using the acetaminophen absorption test which essentially measures gastric emptying of liquids during the first hour and capacity to absorb the drug over 4-6 h, expressed as AUC. The most valid measurements by scintigraphy (solids or liquids) and acetaminophen absorption at 30 or 60 min show that GLP-1-related drugs used in diabetes or obesity retard gastric emptying, and this is associated with reduced glycemia and variable effects on food intake and appetite. GLP-1 agonists and analogs are integral to the management of patients with type 2 diabetes mellitus and obesity. The effects on gastric emptying are reduced with long-acting preparations or long-term use of short-acting preparations as a result of tachyphylaxis. The dual agonists targeting GLP-1 and another receptor (GIP) do not retard gastric emptying, based on reports to date. In summary, GLP-1 agonists and analogs are integral to the management of patients with type 2 diabetes mellitus and obesity, and their effects are mediated, at least in part, by retardation of gastric emptying.

Induction of Meal-related Symptoms as a Novel Mechanism of Action of the Duodenal-Jejunal Bypass Sleeve

BACKGROUND

Treatment with a duodenal-jejunal bypass sleeve (DJBS) induces clinically significant weight loss, but little is known about the mechanisms of action of this device.

AIM

The aim of this study was to characterize the mechanisms of action of the DJBS and determine the durability of weight loss and metabolic improvements.

MATERIALS AND METHODS

We studied a cohort of 19 subjects with severe obesity and type 2 diabetes (baseline body mass index: 43.7±5.3 kg/m). Anthropometry, body composition, blood pressure, biochemical measures, and dietary intake were monitored for 48 weeks after DJBS implantation, and then for 1 year after device removal. Gastric emptying and triglyceride absorption were measured at baseline, 8 weeks after implant, and within 3 weeks of device explant. Visceral sensory function was assessed at baseline, 4 weeks after implant, and within 3 weeks after explant.

RESULTS

Significant weight loss (P<0.01) occurred following DJBS placement, with a mean weight reduction of 17.0±6.5% at 48 weeks. The symptom burden following a standardized nutrient challenge was increased after DJBS implantation (P<0.05), returning to baseline after DJBS removal. Neither gastric emptying nor triglyceride absorption changed with the device in situ. A significant reduction in energy intake was observed [baseline: 7703±2978 kJ (1841±712 kcal), 24 weeks: 4824±2259 kJ (1153±540 kcal), and 48 weeks: 4474±1468 kJ (1069±351 kcal)]. After 1 year, anthropometry remained significantly improved, but there was no durable impact on metabolic outcomes.

CONCLUSIONS

DJBS treatment resulted in substantial weight loss. Weight loss is related to reduced caloric intake, which seems linked to an augmented upper gastrointestinal symptom response, but not altered fat absorption.

Association between delayed gastric emptying and upper gastrointestinal symptoms: a systematic review and meta-analysis

BACKGROUND

The relationship between delayed gastric emptying and upper GI symptoms (UGI Sx) is controversial.

OBJECTIVE

To assess association between gastric emptying and UGI Sx, independent of treatment.

DESIGN

We performed a systematic review and meta-analysis of the literature from 2007 to 2017, review of references and additional papers identified by content expert. We included studies evaluating the association between gastric emptying and nausea, vomiting, early satiety/postprandial fullness, abdominal pain and bloating. Covariate analyses included optimal gastric emptying test method, gastric emptying type (breath test or scintigraphy) and patient category. Meta-regression compared the differences based on type of gastric emptying tests.

RESULTS

Systematic review included 92 gastric emptying studies (26 breath test, 62 scintigraphy, 1 ultrasound and 3 wireless motility capsule); 25 of these studies provided quantitative data for meta-analysis (15 scintigraphy studies enrolling 4056 participants and 10 breath test studies enrolling 2231 participants). Meta-regression demonstrated a significant difference between optimal and suboptimal gastric emptying test methods when comparing delayed gastric emptying with nausea and vomiting. On evaluating studies using optimal gastric emptying test methodology, there were significant associations between gastric emptying and nausea (OR 1.6, 95% CI 1.4 to 1.8), vomiting (OR 2.0, 95% CI 1.6 to 2.7), abdominal pain (OR 1.5, 95% CI 1.0 to 2.2) and early satiety/fullness (OR 1.8, 95% CI 1.2 to 2.6) for patients with UGI Sx; gastric emptying and early satiety/fullness in patients with diabetes; gastric emptying and nausea in patients with gastroparesis.

CONCLUSIONS

The systematic review and meta-analysis supports an association between optimally measured delayed gastric emptying and UGI Sx.

Evaluation of Patients with Suspected Gastroparesis

There is substantial overlap between the symptoms of gastroparesis and a variety of alternative disorders. These conditions include rumination syndrome, drug-induced gastric emptying delay, cannabinoid hyperemesis syndrome, and eating disorders, which can be identified based on the history alone. The remaining patients require a diagnostic approach of physical examination, laboratory tests, evaluation with esophagogastroduodenoscopy or contrast radiography, and a test to measure gastric emptying. Symptomatic patients who have normal nutritional status and gastric emptying that is either normal or mildly delayed should be diagnosed with functional dyspepsia, whereas patients with moderate or severe gastric emptying delay are diagnosed with gastroparesis.

Expert consensus document: Advances in the diagnosis and classification of gastric and intestinal motility disorders

Disturbances of gastric, intestinal and colonic motor and sensory functions affect a large proportion of the population worldwide, impair quality of life and cause considerable health-care costs. Assessment of gastrointestinal motility in these patients can serve to establish diagnosis and to guide therapy. Major advances in diagnostic techniques during the past 5-10 years have led to this update about indications for and selection and performance of currently available tests. As symptoms have poor concordance with gastrointestinal motor dysfunction, clinical motility testing is indicated in patients in whom there is no evidence of causative mucosal or structural diseases such as inflammatory or malignant disease. Transit tests using radiopaque markers, scintigraphy, breath tests and wireless motility capsules are noninvasive. Other tests of gastrointestinal contractility or sensation usually require intubation, typically represent second-line investigations limited to patients with severe symptoms and are performed at only specialized centres. This Consensus Statement details recommended tests as well as useful clinical alternatives for investigation of gastric, small bowel and colonic motility. The article provides recommendations on how to classify gastrointestinal motor disorders on the basis of test results and describes how test results guide treatment decisions.

Functional Dyspepsia and Gastroparesis

BACKGROUND

Upper gastrointestinal disorders typically present with common symptoms. The most relevant non-mucosal diseases are gastroparesis, functional dyspepsia and rumination syndrome. The literature pertaining to these 3 conditions was reviewed.

KEY MESSAGES

Gastroparesis is characterized by delayed gastric emptying in the absence of mechanical obstruction of the stomach. The cardinal symptoms include postprandial fullness (early satiety), nausea, vomiting and bloating. The most frequently encountered causes of these symptoms are mechanical obstruction (pyloric stenosis), iatrogenic disease, gastroparesis, functional dyspepsia, cyclical vomiting and rumination syndrome. The most common causes of gastroparesis are neuropathic disorders such as diabetes, idiopathic, post-vagotomy and scleroderma among myopathic disorders. Principles of management of gastroparesis include exclusion of mechanical obstruction with imaging and iatrogenic causes with careful medication and past surgical history. Prokinetics and anti-emetics are the mainstays of treatment. Functional dyspepsia is characterized by the same symptoms as gastroparesis; in addition to delayed gastric emptying, pathophysiological abnormalities include accelerated gastric emptying, impaired gastric accommodation and gastric or duodenal hypersensitivity to distension and nutrients. Novel treatments include tricyclic antidepressants in patients with normal gastric emptying, acotiamide (acetyl cholinesterase inhibitor) and 5-HT1A receptor agonists such as buspirone. Rumination syndrome is characterized by repetitive regurgitation of gastric contents occurring within minutes after a meal. Episodes often persist for 1-2 h after the meal, and the regurgitant consists of partially digested food that is recognizable in its taste. Regurgitation is typically effortless or preceded by a sensation of belching. This has been summarized as a 'meal in, meal out, day in, day out' behavior for weeks or months, differentiating rumination from gastroparesis. Patients often have a background of psychological disorder or a prior eating disorder. Treatment is based on behavioral modification.

CONCLUSION

Precise identification of the cause and pathophysiology of upper gastrointestinal symptoms is essential for optimal management.

In vitro development and validation of a non-invasive (13)C-stable isotope assay for ornithine decarboxylase

Oesophageal cancer is a significant cause of cancer related mortality, with increasing incidence worldwide. Ornithine decarboxylase (ODC) is an enzyme involved in polyamine synthesis and cellular proliferation, and ODC expression and activity has been implicated as a prognostic marker of oesophageal cancer. This study aimed to develop and optimise an in vitro (13)C-stable isotope assay for ODC activity as a non-invasive marker of oesophageal cancer. Experiments were performed in triplicate (n  =  3/group/cell line) using Caco2, HeLa, Flo-1, OE33, TE7 and OE21 cell lines (colorectal, cervical, oesophageal adenocarcinoma and oesophageal squamous carcinoma respectively). Following addition of 2mM (13)C-ornithine to cells, 10 ml gas samples were collected from the headspace every 20 min for a total of five hours. Gas samples were analysed using isotope ratio mass spectrometry to quantify (13)CO2. Assay specificity was determined using the selective ODC inhibitor, N-(4'-Pyridoxil)-Ornithine(BOC)-OMe (POB). All data is expressed as δ (13)CO2 from baseline. High ODC activity was detected by (13)C-ornithine assay in Caco2 (32.00  ±  1.12 δ (13)CO2) in contrast to HeLa cells (5.44  ±  0.14 δ (13)CO2) cells. POB inhibited activity in Caco2 cells to 12.87  ±  1.10 δ (13)CO2. Differential ODC activity was detected in all oesophageal cancer cells, and 53 h incubation of cell lines with POB reduced activity by 72%, 56%, 64% and 69% in the Flo-1, OE33, OE21 and TE7 cell lines respectively. We have shown that ODC activity can be selectively detected by a non-invasive, stable-isotope (13)C-ornithine assay. ODC activity was detected in all oesophageal cancer cell lines in vitro. Further studies are indicated to quantify ODC activity in oesophageal cancer patients.

Microgravity Simulated by the 6° Head-Down Tilt Bed Rest Test Increases Intestinal Motility but Fails to Induce Gastrointestinal Symptoms of Space Motion Sickness

BACKGROUND

Space motion sickness (SMS) is the most relevant medical problem during the first days in microgravity. Studies addressing pathophysiology in space face severe technical challenges and microgravity is frequently simulated using the 6° head-down tilt bed rest test (HDT).

AIM

We were aiming to test whether SMS could be simulated by HDT, identify related changes in gastrointestinal physiology and test for beneficial effects of exercise interventions.

METHODS

HDT was performed in ten healthy individuals. Each individual was tested in three study campaigns varying by a 30-min daily exercise intervention of either standing, an upright exercise regimen, or no intervention. Gastrointestinal symptoms, stool characteristics, gastric emptying time, and small intestinal transit were assessed using standardized questionnaires, (13)C octanoate breath test, and H2 lactulose breath test, respectively, before and at day 2 and 5 of HDT.

RESULTS

Individuals described no or minimal gastrointestinal symptoms during HDT. Gastric emptying remained unchanged relative to baseline data collection (BDC). At day 2 of HDT the H₂ peak of the lactulose test appeared earlier (mean ± standard error for BDC-1, HDT2, HDT5: 198 ± 7, 139 ± 18, 183 ± 10 min; p: 0.040), indicating accelerated small intestinal transit. Furthermore, during HDT, stool was softer and stool mass increased (BDC: 47 ± 6, HDT: 91 ± 12, recovery: 53 ± 8 g/day; p: 0.014), indicating accelerated colonic transit. Exercise interventions had no effect.

CONCLUSION

HDT did not induce symptoms of SMS. During HDT, gastric emptying remained unchanged, but small and large intestinal transit was accelerated.

The use of SmartPill for gastric monitoring

Testing to define delayed gastric emptying is required to diagnose gastroparesis; rapid emptying is found in other patients. Commonly performed methods of gastric emptying testing include scintigraphy and breath testing. The SmartPill wireless motility capsule (WMC) system is US FDA-approved for evaluating suspected delayed emptying in gastroparesis and functional dyspepsia. The device measures transit in the stomach, small intestine, and colon by detecting characteristic pH transitions; and quantifies pressure waves in each gut region. WMC gastric emptying times correlate with scintigraphic measures. Incremental benefits of WMC testing in patients with suspected gastroparesis include delineation of pressure abnormalities and small intestinal and colonic transit delays. Acceptance of trial data confirming usefulness of WMC testing in suspected gastric motor disorders has been hampered by small sample sizes and design limitations. Ongoing multicenter studies will validate the utility of WMC methods in patients with suspected gastroparesis and other upper gastrointestinal motor disorders.

Dietary actinidin from kiwifruit (Actinidia deliciosa cv. Hayward) increases gastric digestion and the gastric emptying rate of several dietary proteins in growing rats

Dietary actinidin influences the extent to which some dietary proteins are digested in the stomach, and it is hypothesized that the latter modulation will in turn affect their gastric emptying rate (GE). In this study, the effect of dietary actinidin on GE and gastric digestion of 6 dietary protein sources was determined in growing rats. Each dietary protein source [beef muscle, gelatin, gluten, soy protein isolate (SPI), whey protein isolate, and zein] was included in 2 semisynthetic diets as the sole nitrogen source. For each protein source, 1 of the 2 diets contained actinidin [76.5 U/g dry matter (DM)] in the form of ground freeze-dried green kiwifruit (Actinidia deliciosa cv. Hayward), whereas the other diet contained freeze-dried gold kiwifruit (Actinidia chinensis cv. Hort16A), which is devoid of actinidin (3.4 U/g DM). For both diets, dietary kiwifruit represented 20% of the diet on a DM basis. The real-time GE was determined in rats gavaged with a single dose of the diets using magnetic resonance spectroscopy over 150 min (n = 8 per diet). Gastric protein digestion was determined based on the free amino groups in the stomach chyme collected from rats fed the diets (n = 8 per diet) that were later killed. GE differed across the protein sources [e.g., the half gastric emptying time (T(½)) ranged from 157 min for gluten to 266 min for zein] (P < 0.05). Dietary actinidin increased the gastric digestion of beef muscle (0.6-fold), gluten (3.2-fold), and SPI (0.6-fold) and increased the GE of the diets containing beef muscle (43% T(½)) and zein (23% T(½); P < 0.05). There was an inverse correlation between gastric protein digestion and DM retained in the stomach (r = -0.67; P < 0.05). In conclusion, dietary actinidin increased gastric protein digestion and accelerated the GE for several dietary protein sources. GE may be influenced by gastric protein digestion, and dietary actinidin can be used to modulate GE and protein digestion in the stomach of some dietary protein sources but not others.

Actinidin from kiwifruit (Actinidia deliciosacv. Hayward) increases the digestion and rate of gastric emptying of meat proteins in the growing pig

The present study aimed to investigate the effect of dietary actinidin on the kinetics of gastric digestion of beef muscle proteins and on the rate of stomach emptying in growing pigs. For this purpose, 120 pigs (mean body weight 28 (sd2·9) kg) were fed beef muscle protein-based diets containing either actinidin (fresh green kiwifruit pulp or gold kiwifruit pulp supplemented with purified actinidin) or no actinidin (fresh gold kiwifruit pulp or green kiwifruit pulp with inactivated actinidin). Additionally, fifteen pigs were fed with a protein-free diet to determine the endogenous protein flow. Pigs were euthanised at exactly 0·5, 1, 3, 5 and 7 h postprandially (n6 per time point for each kiwifruit diet andn3 for protein-free diet). Stomach chyme was collected for measuring gastric retention, actinidin activity, individual beef muscle protein digestion based on SDS–PAGE and the degree of hydrolysis based on the appearance of free amino groups. The stomach emptying of DM and N was faster when actinidin was present in the diet (P< 0·05): the half gastric emptying time of DM was 137v. 172 min ( ± 7·4 min pooled standard error) for the diets with and without actinidin, respectively. The presence of dietary actinidin in the stomach chyme increased the digestion of beef muscle protein (P< 0·05) and, more specifically, those proteins with a high molecular weight (>34 kDa;P< 0·05). In conclusion, dietary actinidin fed in the form of fresh green kiwifruit increased the rate of gastric emptying and the digestion of several beef muscle proteins.

A ghrelin agonist fails to show benefit in patients with diabetic gastroparesis: let's not throw the baby out with the bath water

Ghrelin is the endogenous ligand for the growth hormone secretagogue-1a receptor and is a potential target for treatment of gastroparesis. This viewpoint assesses the potential role of ghrelin agonists in the treatment of gastroparesis through a review of the early phase, randomized, controlled trials of ghrelin agonists in patients with diabetes and, either, delayed gastric emptying at the time of the trial or symptoms at the time of the trial, and prior documentation of delayed gastric emptying of solids. Whereas recent experience with ghrelin agonists that have a macrocycle structure (TZP-101, TZP-102) has not confirmed earlier promising results, there is little evidence that ghrelin receptors downregulate with repeated treatment, in contrast to motilin receptors. Phase IIa clinical trials performed with a different agent (RM-131, which is a small molecule ghrelin agonist) suggest that, as a class, ghrelin agonists may be efficacious in stimulating gastric emptying. It is premature to dismiss ghrelin agonists as potential therapies for gastroparesis.

Current management strategies and emerging treatments for functional dyspepsia

Functional dyspepsia refers to painful and nonpainful symptoms that are perceived to arise in the upper digestive tract but are not secondary to organic, systemic or metabolic diseases. The symptoms of this syndrome often overlap with those of GERD and IBS, making its management far from simple. If Helicobacter pylori infection is diagnosed in patients with functional dyspepsia, it should be treated. In patients with mild or intermittent symptoms, reassurance and lifestyle advice might be sufficient; in patients not responding to these measures, or in those with more severe symptoms, drug therapy should be considered. Both PPIs and prokinetics can be used in initial empirical pharmacotherapy based on symptom patterns--a PPI is more likely to be effective in the presence of retrosternal or epigastric burning or epigastric pain, whereas a prokinetic is more effective in dyspepsia with early satiation or postprandial fullness. Although combinations of PPIs and prokinetics might have additive symptomatic effects, single-drug therapy is initially preferable. Antidepressants or referral to a psychiatrist or psychotherapist can be considered in nonresponders and in those whose symptoms have a marked effect on daily functioning. Despite extensive research, functional dyspepsia treatment often remains unsatisfactory. Better characterization of dyspeptic subgroups and understanding of underlying mechanisms will enable treatment advances to be made in the future.

Clinical guideline: management of gastroparesis

This guideline presents recommendations for the evaluation and management of patients with gastroparesis. Gastroparesis is identified in clinical practice through the recognition of the clinical symptoms and documentation of delayed gastric emptying. Symptoms from gastroparesis include nausea, vomiting, early satiety, postprandial fullness, bloating, and upper abdominal pain. Management of gastroparesis should include assessment and correction of nutritional state, relief of symptoms, improvement of gastric emptying and, in diabetics, glycemic control. Patient nutritional state should be managed by oral dietary modifications. If oral intake is not adequate, then enteral nutrition via jejunostomy tube needs to be considered. Parenteral nutrition is rarely required when hydration and nutritional state cannot be maintained. Medical treatment entails use of prokinetic and antiemetic therapies. Current approved treatment options, including metoclopramide and gastric electrical stimulation (GES, approved on a humanitarian device exemption), do not adequately address clinical need. Antiemetics have not been specifically tested in gastroparesis, but they may relieve nausea and vomiting. Other medications aimed at symptom relief include unapproved medications or off-label indications, and include domperidone, erythromycin (primarily over a short term), and centrally acting antidepressants used as symptom modulators. GES may relieve symptoms, including weekly vomiting frequency, and the need for nutritional supplementation, based on open-label studies. Second-line approaches include venting gastrostomy or feeding jejunostomy; intrapyloric botulinum toxin injection was not effective in randomized controlled trials. Most of these treatments are based on open-label treatment trials and small numbers. Partial gastrectomy and pyloroplasty should be used rarely, only in carefully selected patients. Attention should be given to the development of new effective therapies for symptomatic control.

Comprehensive assessment of gastric emptying with a stable isotope breath test

BACKGROUND

The [(13)C]-Spirulina platensis gastric emptying breath test (GEBT) with five samples is accurate relative to scintigraphy. This study was primarily designed to further validate this GEBT using a slightly different process for incorporating [(13)C] in Spirulina and to evaluate the utility of additional samples for assessing early gastric emptying.

METHODS

After a 223 kcal, test meal labeled with (99m) Tc and [(13)C]-S. platensis, scintigraphic images, and five breath samples (45, 90, 120, 180, and 240 min, GEBT5) were collected in 14 controls (Part A). In Part B, nine breath samples were collected at 15, 30, 45, 60, 90, 120, 150, 180, and 240 min (GEBT9) in 30 subjects (15 controls, 15 dyspepsia). Using correlation between [(13)C] breath excretion and scintigraphic emptying, lag time (t(10), time for 10% emptying), emptying at 30 min (GE(30)), and half time (t(50)) were estimated for GEBT5 (Parts A and B) and GEBT9 (Part B).

KEY RESULTS

Half time values for scintigraphy, GEBT5, and GEBT9 were highly concordant. t(10) by GEBT9 (90%CI, 6-15 min) was more strongly correlated [CCC 0.80 (95% CI, 0.63-0.90)] with scintigraphy (90% CI, 5-12 min), than GEBT5 [10-19 min, CCC 0.73 (95% CI, 0.54-0.85)]. The correlation between estimated values (GEBT9) and linearly interpolated values (GEBT5) was closer at 60 [CCC 0.95 (95% CI, 0.91-0.97)] than 30 min [CCC 0.81 (95% CI, 0.71-0.89)].

CONCLUSIONS & INFERENCES

The [(13) C]-S. platensis GEBT can accurately measure GE. While 5- and 9-samples are equally accurate for measuring t(50), GEBT9 provides a more comprehensive assessment of early GE (t(10) and GE(30)).

A semi-mechanistic gastric emptying pharmacokinetic model for (13)C-octanoic acid: an evaluation using simulation

The aim of this paper is to assess the performance of a new mechanistic model for analysing (13)C-octanoic acid breath test data using simulation studies. The (13)C-octanoic acid breath test is widely used for indirect assessment of the rate of gastric emptying and it is yet to achieve universal acceptance due to inconsistencies when the results are compared with simultaneous and direct measurements using scintigraphy. The new semi-mechanistic model has five separate compartments; stomach, intestine, central and peripheral body and breath compartments. Stomach and breath profiles were simulated for 50 individuals under four conditions: variability on all parameters; no variability on the rate constant of gastric emptying and the rate constant of absorption; variability on the rate constant of gastric emptying and the rate constant of absorption only; and no variability on all parameters. A mono-exponential model was fitted to the stomach profile and the new semi-mechanistic model and three other widely used methods were fitted to the breath profiles. The gastric emptying half times from stomach profiles correlate better (R(2)=1,1,1,1 for the four conditions) with the half emptying times from the semi-mechanistic model compared with half emptying times from the modified exponential model (R(2)=0.72,0.53,0.88,1), Ghoos method (R(2)=0.72,0.54,0.88,1) and Wagner-Nelson method (R(2)=0.79,0.68,0.89,1) for the four simulation studies. The semi-mechanistic model is very effective for the assessment of GE using the (13)C-octanoic acid breath test and could be applied in the development of drugs that influence GE.

Structural identifiability analysis of pharmacokinetic models using DAISY: semi-mechanistic gastric emptying models for 13C-octanoic acid

Structural identifiability analysis is necessary for efficient parameter estimation and it is concerned with determination of whether the parameters in a model can be identified from specified experiments with perfect input-output data. Structural identifiability analysis is very important in mathematical modelling of biological and biomedical experiments and should be considered at the design stage of these experiments. There are three possible outcomes from a structural identifiability analysis; globally/uniquely identifiable, locally/non-uniquely identifiable or non-identifiable/unidentifiable. An ideal outcome is a globally/uniquely identifiable model, however a locally/non-uniquely identifiable outcome can help to identify areas of the model or experiment that need improvement. Despite the importance of structural identifiability analysis, it is still not widely used due to the heavy computational burden involved and the lack of software. A new software package, DAISY, that implemented differential algebra for identifiability analysis was recently released. DAISY is freely available, easy to use and does not require any high-level programming skill. The (13)C-octanoic acid breath test is now widely used for assessing the rate of gastric emptying in patients. Unlike scintigraphy, which is the gold standard and is a direct measure of the rate of gastric emptying, the (13)C-octanoic acid breath test is an indirect method for assessing the rate of gastric emptying. However the (13)C-octanoic acid breath test is cheaper, safer and easy to perform. Because the rate of excretion of (13)CO(2) in breath does not only reflect the rate of gastric emptying but other processes involved between the ingestion of (13)C-octanoic acid and elimination of (13)CO(2) in breath, the parameters commonly derived from the excretion data are not direct measures of gastric emptying. The aim of this paper was to propose a new semi-mechanistic model for the analysis of (13)C-octanoic acid breath excretion data and demonstrate the use of DAISY to assess the identifiability of the model. One- and two-compartment disposition models were linked to a model which has separate compartments for the stomach, intestine and breath. To obtain a globally identifiable model, a repeated (13)C-octanoic breath test in the same individual experimental design was also investigated and this adds a separate stomach compartment to the model. Finally the gastric emptying rate constant from the first (13)C-octanoic breath test was constrained to be the same as the absorption rate constant from the intestine. From the structural identifiability analysis carried out in DAISY, the model based on two experiments (baseline and treatment) and a constraint is globally identifiable. In summary, the present work describes a new semi-mechanistic model that will allow efficient and reliable assessment of the rate of gastric emptying from the (13)C-octanoic breath test.

Evaluation of gastrointestinal transit in clinical practice: position paper of the American and European Neurogastroenterology and Motility Societies

BACKGROUND

Disorders of gastrointestinal (GI) transit and motility are common, and cause either delayed or accelerated transit through the stomach, small intestine or colon, and affect one or more regions. Assessment of regional and/or whole gut transit times can provide direct measurements and diagnostic information to explain the cause of symptoms, and plan therapy.

PURPOSE

Recently, several newer diagnostic tools have become available. The American and European Neurogastroenterology and Motility Societies undertook this review to provide guidelines on the indications and optimal methods for the use of transit measurements in clinical practice. This was based on evidence of validation including performance characteristics, clinical significance, and strengths of various techniques. The tests include measurements of: gastric emptying with scintigraphy, wireless motility capsule, and (13)C breath tests; small bowel transit with breath tests, scintigraphy, and wireless motility capsule; and colonic transit with radioopaque markers, wireless motility capsule, and scintigraphy. Based on the evidence, consensus recommendations are provided for each technique and for the evaluations of regional and whole gut transit. In summary, tests of gastrointestinal transit are available and useful in the evaluation of patients with symptoms suggestive of gastrointestinal dysmotility, since they can provide objective diagnosis and a rational approach to patient management.

Effect of alginate on satiation, appetite, gastric function, and selected gut satiety hormones in overweight and obesity

Lack of control of food intake, excess size, and frequency of meals are critical to the development of obesity. The stomach signals satiation postprandially and may play an important role in control of calorie intake. Sodium alginate (based on brown seaweed Laminaria digitata) is currently marketed as a weight loss supplement, but its effects on gastric motor functions and satiation are unknown. We evaluated effects of 10 days treatment with alginate or placebo on gastric functions, satiation, appetite, and gut hormones associated with satiety in overweight or obese adults. We conducted a randomized, 1:1, placebo-controlled, allocation-concealed study in 48 overweight or obese participants with excluded psychiatric comorbidity and binge eating disorder. All underwent measurements of gastric emptying (GE), fasting, and postprandial gastric volumes (GVs), postprandial satiation, calorie intake at a free choice meal and selected gut hormones after 1 week of alginate (three capsules vs. matching placebo per day, ingested 30 min before the main meal). Six capsules were ingested with water 30 min before the GE, GV, and satiation tests on days 8-10. There were no treatment group effects on GE or volumes, gut hormones (ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), peptide YY (PYY)), satiation, total and macronutrient calorie intake at a free choice meal. There was no difference detected in results between obese and overweight patients. Alginate treatment for a period of 10 days showed no effect on gastric motor functions, satiation, appetite, or gut hormones. These results question the use of short-term alginate treatment for weight loss.

Influence of clinical parameters on the results of 13C-octanoic acid breath tests: examination of different mathematical models in a large patient cohort

It is assumed, although not proven, that 13CO2-excretion following ingestion of 13C-octanoic acid (13C-OA) does not only depend on gastric emptying (GE) but also on absorption and metabolism of 13C-OA and endogenous CO2-production. Our aims were (i) to test the effects of patient characteristics and of diseases that may impair 13C-OA-metabolism on GE parameters. (ii) To compare different GE endpoints. Therefore, we investigated effects of age, gender, BMI and diseases with potential impact on 13C-OA-metabolism (including pancreatic, liver and lung disease, diabetes, IBD) on cumulative 4h-13CO2-excretion (4h-CUM) and T1/2 calculated by non-linear regression model (NL, determined by shape of breath test curve) and generalized linear regression model (GLR, reflects absolute 13CO2-excretion) in 1279 patients and 19 healthy controls who underwent a standardized 13C-OA-breath test. Digestive and metabolic disturbances hardly influenced 4h-CUM or T1/2 calculated by NL or GLR models. In the multivariate linear regression models, 4h-CUM was significantly predicted by diabetes adjusted for age, gender and IBD but influence of these parameters was small (R2 = 0.028, P < 0.0001). T1/2(NL) and 4h-CUM were weakly correlated, even after exclusion of tests with unrealistically high estimates for T1/2(NL) (n = 1095, R(2) = 0.029, P < 0.0001). Conversely, 4h-CUM was closely associated with T(1/2)(GLR) (exponential correlation, R(2) = 0.774, P < 0.00001, n = 1279). We conclude that influences of digestive and metabolic disturbances on 13CO2-excretion following 13C-OA-application are generally low. Thus, our findings resolve an important criticism of methods using absolute 13CO2-excretion for evaluation of 13C-OA-breath tests and suggest that such models may correctly identify T1/2 in a mixed patient population.

Will the 13C-octanoic acid breath test ever replace scintigraphy as the gold standard to assess gastric emptying?

The applicability of the 13C-octanoic acid breath test for the assessment of gastric emptying is discussed. In the current issue of this journal, Keller and her colleagues described the application of different mathematical models for analysis of the 13C-octanoic acid test in a very large patient population.