Comparison between gastric scintigraphy and the [13C]-acetate breath test with Wagner-Nelson analysis in humans

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.

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.

13 C-gastric emptying breath tests: Clinical use in adults and children

¹³ C-gastric emptying breath tests (¹³ C-GEBT) are validated, reliable, and non-invasive tools for measurement of gastric emptying (GE) velocity of solids and liquids without radiation exposure or risk of toxicity. They are recommended and routinely used for clinical purposes in adult as well as pediatric patients and can be readily performed onsite or even at the patient's home. However, the underlying methodology is rather complex and test results can be influenced by dietary factors, physical activity, concurrent diseases, and medication. Moreover, epidemiological factors can influence gastric emptying as well as production and exhalation of ¹³ CO₂ , which is the ultimate metabolic product measured for all ¹³ C-breath tests. Accordingly, in this issue of Neurogastroenterology & Motility, Kovacic et al. report performance of the ¹³ C-Spirulina breath test in a large group of healthy children and show significant effects of gender, pubertal status, and body size on test results. The purpose of this mini-review is to evaluate the clinical use of ¹³ C-GEBT in adults and children, exploring available protocols, analytical methods, and essential prerequisites for test performance, as well as the role of GE measurements in the light of the current discussion on relevance of delayed GE for symptom generation.

Indirect vs direct assessment of gastric emptying: A randomized crossover trial comparing C-isotope breath analysis and MRI

BACKGROUND

Indirect methods to assess gastric emptying (GE), such as ¹³ C breath tests (BT), are commonly used. However, BT usually use a sampling time of 4+ hours. The current study aims to assess the validity of BT for four liquid meals differing in physicochemical properties. To this aim, we compared them to MRI GE-measurements.

METHODS

Fifteen healthy males (age 22.6 ± 2.4 years, BMI 22.6 ± 1.8 kg/m² ) participated in a randomized 2 × 2 crossover experiment. Test foods were liquid meals, which were either thin/thick and 100/500 kcal, labeled with 100 mg of ¹³ C-octanoate. GE was measured with MRI and assessed by ¹³ C recovery from breath. Participants were scanned every 10 minutes and at six time points breath samples were collected up to t = 90 minutes. Two curves were fitted to the data to estimate emptying halftime (t_{50 Ghoos} and t_{50 Bluck} ). T₅₀ times were ranked per participant and compared between methods.

KEY RESULTS

On average, MRI and BT showed similar t₅₀ rankings for the four liquid meals. In comparison to MRI, t_{50 Ghoos} overestimated, while t_{50 Bluck} underestimated GE time_. Moreover, more viscous foods were overestimated. In most participants individual t₅₀ time rankings differed significantly between methods.

CONCLUSIONS & INFERENCES

BT can assess relative emptying differences on group level and collecting breath data for 90 minutes constitutes a lower burden for participants and the research facility. However, BT has severe shortcomings compared to MRI for individual GE assessment. Notably, food matrix effects should be considered when interpreting the results of BT.

Gastric Emptying of Liquids in Children

OBJECTIVES

The present study was performed to determine normal values for gastric half-emptying time (t1/2GE) of liquids in healthy children.

METHODS

Gastric emptying (GE) of a standardized test milk-drink measured with technetium scintigraphy and the C-acetate breath test (C-ABT) was compared in 19 children ages between 4 and 15 years with upper gastrointestinal symptoms. The C-ABT was subsequently used to determine normal values for GE of the same liquid test meal in 133 healthy children ages between 1 and 17 years.

RESULTS

In the group of children with upper gastrointestinal symptoms, the results showed a significant correlation (r = 0.604, P = 0.0006) between t1/2GE measured with both techniques. In the group of healthy children, the results of t1/2GE showed that there was no influence of age, sex, weight, height, and body mass index on GE.

CONCLUSIONS

Normal values for GE of a standardized test milk-drink in healthy children were determined with the C-ABT. This technique is considered reliable and is well accepted by the patients.

On the validity of the (13) C-acetate breath test for comparing gastric emptying of different liquid test meals: a validation study using magnetic resonance imaging

BACKGROUND

(13) C-acetate breath testing (BT) is applied to assess and compare gastric emptying of liquid meals. Gastric half-emptying times (t50 ) from BT show offsets compared to t50 values from γ-scintigraphy and ultrasonography. Linear transformations have been proposed to correct these offsets. This investigation critically validates the BT for the assessment of liquid gastric emptying by using simultaneously recorded meal and total gastric content volume emptying data from magnetic resonance imaging (MRI).

METHODS

Data were collected during a recently published double-blind, randomized, cross-over MRI gastric emptying study of three (13) C-labeled enteral formulas differing in protein sources (PMID: 24699556). Breath testing-derived t50 was computed with the analysis methods commonly applied in gastric emptying research, i.e., the exponential-beta function and the Wagner-Nelson (WN) method, respectively.

KEY RESULTS

Breath testing t50 values from exponential-beta function and WN method showed a positive and negative offset to MRI data, respectively. Linear regression detected low concordance between MRI and both BT methods revealing meal specific and emptying rate-dependent offsets. The WN method showed worse agreement and correlation with MRI emptying data. Breath testing rather reflected meal volume than total gastric content volume emptying.

CONCLUSIONS & INFERENCES

This validation study indicates that the (13) C-acetate breath test may not be applied to compare gastric emptying of arbitrary liquid meals without prior validation by imaging methods. t50 values from BT are biased by (i) the properties of the meal and (ii) the selected method used for (13) CO2 exhalation analysis. No linear transformation common for all meals was applicable to correct the offsets between BT and MRI.

Assessment of motor function of the remnant stomach by ¹³C breath test with special reference to gastric local resection

BACKGROUND

Indications for gastric local resection (LR) include gastrointestinal stromal tumors, neuroendocrine tumors, and early gastric cancer. LR is expected to preserve physiological function and ameliorate postgastrectomy syndrome.

METHODS

Gastric emptying was assessed by the (13)C-acetate breath test in 20 healthy volunteers (HVs) and 60 gastrectomized patients [distal gastrectomy with Billroth I reconstruction (DGBI) in 26 patients, LR in 34 patients]. For the (13)C breath test, 100 mg of (13)C-acetate sodium salt was mixed in a test meal. Breath samples were collected before intake and during the next 3 h. We compared the gastric reservoir capacity using the gastric retention rate at 5 min (RR5) and gastric emptying by the half emptying time (T½). Patients completed a questionnaire survey about their symptoms, dietary intake, body weight, and restriction of activities of daily living [reflecting quality of life (QOL)].

RESULTS

The RR5 values for the HV, LR, and DGBI groups were 93.7, 90.0, and 45.3* %, respectively (*compared to HV and LR, p < 0.0001). The T½ values were 23.3, 20.2, and 5.9* min, respectively. Dietary intake and body weight change were significantly more reduced in the DGBI group than the LR group (p < 0.05). Subgroup analysis indicated that the reservoir capacity in those with LR at the lesser curvature was more disturbed than that in patients with LR at the greater curvature. The questionnaire showed no differences in those patients' QOL.

CONCLUSIONS

Because the reservoir capacity, the gastric emptying and QOL were maintained, LR is an option for selected patients with early gastric cancer.

Direct comparison of solid-phase gastric emptying times assessed by means of a carbon isotope-labeled sodium acetate breath test and technetium Tc 99m albumin colloid radioscintigraphy in healthy cats

OBJECTIVE

To directly compare solid-phase gastric emptying times assessed by means of a [(13)C]sodium acetate breath test ([(13)C]-SABT) and technetium Tc 99m albumin colloid radioscintigraphy ((99m)Tc-ACR) in healthy cats.

ANIMALS

12 healthy cats.

PROCEDURE

After ingestion of a test meal containing 50 mg of [(13)C]sodium acetate and 250 MBq of (99m)Tc-albumin colloid, each cat underwent simultaneous [(13)C]-SABT and (99m)Tc-ACR on 2 consecutive days. Breath samples and scintigrams were acquired at 30, 60, 90, 120, 150, 180, 210, 240, 300, 360, 480, and 600 minutes after meal ingestion. Quartiles of gastric emptying (25%, 50%, and 75%) were calculated for breath test analysis by use of the area under the curve of the (13)C:(12)C ratio. Quartiles of gastric emptying times were extrapolated from the scintigraphic findings by beans of nonlinear curve regression analysis.

RESULTS

Mean ± SD gastric half-emptying (50%) times obtained with [(13)C]-SABT and (99m)Tc-ACR, were 239 ± 28 minutes and 276 ± 59 minutes, respectively. A 2-way repeated-measures ANOVA revealed that mean gastric emptying times determined with [(13)C]-SABT and (99m)Tc-ACR differed significantly. For the stages of gastric emptying, Pearson correlation between the 2 methods was good at 25% (r = 0.655) and weak at 50% (r = 0.588) and 75% (r = 0.566)of gastric emptying.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the [(13)C]-SABT can be a valid alternative to (99m)Tc-ACR in healthy cats; it was easy to perform, was tolerated well by the cats, and had acceptable correlation to scintigraphic findings at gastric emptying of 25%, 50% and 75%. Studies in cats with delayed gastric emptying will be needed to verify the validity of the [(13)C]-SABT.

Mapping glucose-mediated gut-to-brain signalling pathways in humans

Objectives

Previous fMRI studies have demonstrated that glucose decreases the hypothalamic BOLD response in humans. However, the mechanisms underlying the CNS response to glucose have not been defined. We recently demonstrated that the slowing of gastric emptying by glucose is dependent on activation of the gut peptide cholecystokinin (CCK₁) receptor. Using physiological functional magnetic resonance imaging this study aimed to determine the whole brain response to glucose, and whether CCK plays a central role.

Experimental design

Changes in blood oxygenation level-dependent (BOLD) signal were monitored using fMRI in 12 healthy subjects following intragastric infusion (250 ml) of: 1 M glucose + predosing with dexloxiglumide (CCK₁ receptor antagonist), 1 M glucose + placebo, or 0.9% saline (control) + placebo, in a single-blind, randomised fashion. Gallbladder volume, blood glucose, insulin, and GLP-1 and CCK concentrations were determined. Hunger, fullness and nausea scores were also recorded.

Principal observations

Intragastric glucose elevated plasma glucose, insulin, and GLP-1, and reduced gall bladder volume (an in vivo assay for CCK secretion). Glucose decreased BOLD signal, relative to saline, in the brainstem and hypothalamus as well as the cerebellum, right occipital cortex, putamen and thalamus. The timing of the BOLD signal decrease was negatively correlated with the rise in blood glucose and insulin levels. The glucose + dex arm highlighted a CCK₁-receptor dependent increase in BOLD signal only in the motor cortex.

Conclusions

Glucose induces site-specific differences in BOLD response in the human brain; the brainstem and hypothalamus show a CCK₁ receptor-independent reduction which is likely to be mediated by a circulatory effect of glucose and insulin, whereas the motor cortex shows an early dexloxiglumide-reversible increase in signal, suggesting a CCK₁ receptor-dependent neural pathway.

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We have identified two distinct CNS responses to glucose in man.

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A CCK1 receptor (CCK1R)-dependent BOLD signal increase in the motor cortex.

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A CCK1R-independent BOLD signal decrease in the brainstem and hypothalamus.

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The BOLD signal decrease was mediated by changes in blood glucose and insulin,

Diabetic gastroparesis: recent insights into pathophysiology and implications for management

Delayed gastric emptying affects a substantial proportion of patients with long-standing diabetes, and when associated with symptoms and/or disordered glycemic control, affects quality of life adversely. Important clinicopathological insights have recently been gained by the systematic analysis of gastric biopsies from patients with severe diabetic gastroparesis, which may stimulate the development of new therapies in the coming decade. Experience with prokinetic therapies and treatments, such as pyloric botulinum toxin injection and gastric electrical stimulation, has established that relief of symptoms does not correlate closely with acceleration of delayed gastric emptying, and that well-designed controlled trials are essential to determine the efficacy of emerging therapies.

Colestyramine slows gastric emptying of liquids and reduces appetite in healthy subjects

BACKGROUND

There is evidence to suggest that the particulate resin colestyramine, a bile acid sequestrant formerly used as a cholesterol-lowering agent, enhances secretion of the gut hormone cholecystokinin (CCK). Established physiological actions of CCK include inhibition of gastric emptying and induction of satiation. This study evaluated the hypothesis that colestyramine, which is luminally retained, would slow gastric emptying of liquids and suppress appetite in humans.

METHODS

Nine healthy volunteers consumed 500 mL liquid test meals containing 4 g colestyramine, 12 g colestyramine, or control (water alone), on three occasions, in a randomized order. The effect of colestyramine on gastric emptying was determined non-invasively using the (13) C-acetate breath test, and appetite and other gut-centered sensations were rated using visual analog scale questionnaires.

KEY RESULTS

Colestyramine dose dependently slowed liquid gastric emptying compared with control (water) (4 g vs control, ∼20% reduction, P < 0.05; 12 g vs control, ∼35% reduction, P < 0.01). Colestyramine also significantly reduced hunger (4 g vs control, ∼20% reduction, P < 0.01), and the amount of food participants felt able to eat (12 g vs control, ∼32% reduction, P < 0.001), but increased bloating (both doses, P < 0.05), with no effect on ratings of nausea.

CONCLUSIONS & INFERENCES

This study provides the first evidence that colestyramine significantly slows liquid gastric emptying and reduces appetite in healthy humans. Colestyramine therefore presents an attractive gut-brain signaling research tool in that it is not absorbed and thus lacks potentially confounding postabsorptive effects. Furthermore, with clear effects on gastric emptying and appetite, colestyramine now merits consideration as a trial therapeutic strategy for appetite suppression and weight loss.

Pathophysiology of functional dyspepsia

Functional dyspepsia is a highly prevalent and heterogeneous disorder. Functional dyspepsia involves many pathogenic factors, such as gastric motility disorders, visceral hypersensitivity, psychological factors, Helicobacter pylori infection, and excessive gastric acid secretion. The present article provides an overview of pathogenetic factors and pathophysiologic mechanisms.

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.

The role of the gut sweet taste receptor in regulating GLP-1, PYY, and CCK release in humans

The recent identification of sweet taste receptors in the gastrointestinal tract has important implications in the control of food intake and glucose homeostasis. Lactisole can inhibit the sweet taste receptor T1R2/T1R3. The objective was to use lactisole as a probe to investigate the physiological role of T1R2/T1R3 by assessing the effect of T1R2/T1R3 blockade on GLP-1, PYY, and CCK release in response to 1) intragastric administration of nutrients or 2) intraduodenal perfusion of nutrients. The study was performed as a randomized, double-blind, placebo-controlled crossover study that included 35 healthy subjects. In part I, subjects received intragastrically 75 g of glucose in 300 ml of water or 500 ml of a mixed liquid meal with or without lactisole. In part II, subjects received an intraduodenal perfusion of glucose (29.3 g glucose/100 ml; rate: 2.5 ml/min for 180 min) or a mixed liquid meal (same rate) with or without lactisole. The results were that 1) lactisole induced a significant reduction in GLP-1 and PYY but not CCK secretion in both the intragastric and the intraduodenal glucose-stimulated parts (P ≤ 0.05), 2) comparison of the inhibitory effect of lactisole showed a significantly greater suppression of the hormone response in the intragastric part (P = 0.023), and 3) lactisole had no effect on liquid meal-stimulated parameters. We conclude that T1R2/T1R3 is involved in glucose-dependent secretion of satiation peptides. However, the results of the liquid meal-stimulated parts show that the receptor alone is not responsible for peptide secretion.

Intragastric pressure during food intake: a physiological and minimally invasive method to assess gastric accommodation

BACKGROUND

The stomach relaxes upon food intake and thereby provides a reservoir while keeping the intragastric pressure (IGP) low. We set out to determine whether we could use IGP as a measurement for stomach accommodation during food intake.

METHODS

In fasted healthy volunteers (n = 7-17) a manometer and an infusion catheter were positioned in the proximal stomach. After a stabilization period a nutrient drink was intragastrically infused at 15, 30 and 60 mL min(-1). To investigate the effect of impaired accommodation the effect of N(G)-monomethyl-L-arginine (L-NMMA) was examined. The volunteers scored satiation until maximum, when the experiment ended. The IGP was presented as a change from baseline (mean ± SEM) and compared with repeated measures anova.

KEY RESULTS

Independent on the ingestion speed, the IGP decreased initially and gradually increased thereafter. Volunteers scored maximal satiation after 699 ± 62, 809 ± 90 and 997 ± 120 mL nutrient drink infused (15, 30 and 60 mL min(-1) respectively; P < 0.01). Maximum IGP decrease was 3.4 ± 0.5 mmHg after 205 ± 28 mL, 5.1 ± 0.7 mmHg after 212 ± 46 mL, and 5.2 ± 0.7 mmHg after 296 ± 28 mL infused volume [15, 30 and 60 mL min(-1) respectively; not significant (ns)]. Post hoc analysis showed significant correlations between IGP and satiation score increase. During L-NMMA infusion IGP was significantly increased while subjects drank significantly less (816 ± 91 vs 1032 ± 71 mL; P < 0.005). Interestingly, the correlation between IGP increase and satiation score increase did not differ after L-NMMA treatment.

CONCLUSIONS & INFERENCES

The IGP during nutrient drink ingestion provides a minimally invasive alternative to the barostat for the assessment of gastric accommodation. These findings furthermore indicate that IGP is a major determinant of satiation.

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.

Diabetic gastroparesis and its impact on glycemia

Diabetes is the most common cause of gastroparesis and it is now recognized that the relationship between gastric emptying and glycemia is complex and intertwined. Postprandial blood glucose levels influence, and are influenced by, the rate of gastric emptying, highlighting the difficulty in determining which is the cause and which is the effect. Novel diagnostic techniques and therapeutic strategies have been developed for the management of diabetic gastroparesis. This article highlights recent advances in knowledge about diabetic gastroparesis, with an emphasis on the inter-relationships between disordered gastric motor function on glycemia and vice versa, as well as therapeutic strategies for optimizing glycemic control using modulation of gastric emptying.

Gastric emptying of hexose sugars: role of osmolality, molecular structure and the CCK₁ receptor

BACKGROUND

It is widely reported that hexose sugars slow gastric emptying (GE) via osmoreceptor stimulation but this remains uncertain. We evaluated the effects of a panel of hexoses of differing molecular structure, assessing the effects of osmolality, intra-individual reproducibility and the role of the CCK(1) receptor, in the regulation of GE by hexoses.

METHODS

Thirty one healthy non-obese male and female subjects were studied in a series of protocols, using a (13) C-acetate breath test to evaluate GE of varying concentrations of glucose, galactose, fructose and tagatose, with water, NaCl and lactulose as controls. GE was further evaluated following the administration of a CCK(1) receptor antagonist. Three subjects underwent repeated studies to evaluate intra-individual reproducibility.

KEY RESULTS

At 250 mOsmol, a hexose-specific effect was apparent: tagatose slowed GE more potently than water, glucose and fructose (P < 0.05). Fructose (P < 0.05) also slowed GE, but with substantial inter-, but not intra-, individual differences. As osmolality increased further the hexose-specific differences were lost. At 500 mOsmol, all hexoses slowed GE compared with water (P < 0.05), whereas lactulose and saline did not. The slowing of GE by hexose sugars appeared to be CCK(1) receptor-dependent.

CONCLUSIONS & INFERENCES

The effects of hexose sugars on GE appear related to their molecular structure rather than osmolality per se, and are, at least in part, CCK(1) receptor-dependent.

The prokinetic effect of mosapride citrate combined with omeprazole therapy improves clinical symptoms and gastric emptying in PPI-resistant NERD patients with delayed gastric emptying

BACKGROUND

Previous studies have shown that non-erosive reflux disease (NERD) patients are less sensitive to proton pump inhibitor (PPI) treatment than patients with erosive reflux disease. The aim of this study was to investigate whether treatment with prokinetics in addition to omeprazole therapy would improve clinical symptoms, gastric emptying and esophageal peristalsis in PPI-resistant NERD patients with or without delayed gastric emptying.

METHODS

Subjects were 64 consecutive patients presenting with typical symptoms of PPl-resistant NERD (n = 44) and 20 healthy volunteers. PPI-resistant NERD patients underwent mosapride citrate (15 mg/day) and omeprazole (20 mg/day) co-therapy for 12 weeks. We evaluated the clinical symptoms as well as gastric emptying and esophageal manometry before and after combined therapy. We measured both acylated- and des-acylated plasma ghrelin levels by the ELISA method. The primary endopoint was to investigate whether co-administration of mosapride citrate and omeprazole would improve clinical symptoms and gastric emptying in PPI-resistant NERD patients with delayed gastric emptying.

RESULTS

T (max) value in PPI-resistant NERD patients was significantly higher than in healthy volunteers. Combination therapy with the prokinetic agent mosapride citrate and omeprazole significantly improved reflux symptoms and T (max) value in T (max) > 65 min NERD patients. Co-therapy also significantly reduced des-acylated-ghrelin levels in NERD patients with delayed gastric emptying.

CONCLUSIONS

Administration of mosapride citrate in addition to omeprazole improved gastro-esophageal reflux and gastric emptying in PPI-resistant NERD patients with delayed gastric emptying.

Desirable pharmacokinetic properties of (13)C-uracil as a breath test probe of gastric emptying in comparison with (13)C-acetate and (13)C-octanoate in rats

OBJECTIVE

To investigate the possible use of a (13)C-uracil breath test for gastric emptying by evaluating the pharmacokinetic properties of (13)C-uracil in a breath test in rats, in comparison with (13)C-acetate and (13)C-octanoate, traditional (13)C-probes for gastric emptying.

MATERIAL AND METHODS

Absorption of the (13)C-probes from different parts of the gastrointestinal tract was evaluated in fasted rats. (13)C-Uracil breath tests for gastric emptying were carried out in conditions where delayed gastric emptying was induced by clonidine, quinpirole, and propantheline, and in a postoperative ileus model. Following oral administration, we measured residual (13)C-uracil in the stomach and correlated the amount with the breath response.

RESULTS

All the (13)C-probes employed were well absorbed from the intestine after intraduodenal administration. After intragastric administration, (13)C-uracil was not absorbed from the stomach, but (13)C-acetate and (13)C-octanoate were partly absorbed from the stomach. The cumulative (14)C-uracil recovery (%) at 168 h was 92.3, 6.3, or 0.5%, from expired gases, urine, and feces, respectively. Delta(13)C values in (13)C-uracil breath tests were decreased in conditions characterized by delayed gastric emptying. A highly negative correlation was observed between the breath response and the residual ratio of (13)C-uracil in the stomach after oral administration of (13)C-uracil, indicating that (13)C-uracil can be used as an in vivo probe for evaluating gastric emptying in a quantitative manner.

CONCLUSIONS

This study showed that (13)C-uracil has desirable pharmacokinetic properties as an in vivo probe of gastric emptying. It is thus suggested that the (13)C-uracil breath test may be useful for the measurement of gastric emptying in humans.

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.

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

Breath tests (BT) using 13C-substrates have been proposed for the measurement of gastric emptying (GE). The mathematical analysis of the breath 13CO2 excretion that most accurately predicts GE t(1/2) from simultaneous scintigraphy is unresolved. To compare five mathematical methods to estimate GE t(1/2) by BT with t(1/2) from simultaneous scintigraphy. Data acquired from a dual-labelled solid-liquid meal containing 99mTc sulphur colloid and 13C-Spirulina platensis from 57 healthy volunteers were used to compare four mathematical methods reported in the literature [Ghoos method; generalized linear regression (Viramontes); linear regression (Szarka); Wagner-Nelson method] and the total cumulative breath 13CO2 excretion with > or =12 breath samples collected over at least 4 h. The concordance correlation coefficient (CCC) for the t(1/2) results obtained with each method using BT data was compared with the results obtained with scintigraphy. The linear regression and generalized linear regression methods used five samples at 45, 90, 120, 150 and 180 min. All methods, except for the Wagner-Nelson method, resulted in mean GE t(1/2) that approximated t(1/2) obtained with scintigraphy. The highest CCC was observed with the linear regression method. Simple cumulative excretion of breath 13CO2 provides a better CCC than the Ghoos method. The linear regression and generalized linear regression methods (which also require relatively few breath samples) provide the most accurate analyses of breath 13CO2 excretion in stable isotope GEBT.

Sweetness and bitterness taste of meals per se does not mediate gastric emptying in humans

In cell line and animal models, sweet and bitter tastants induce secretion of signaling peptides (e.g., glucagon-like peptide-1 and cholecystokinin) and slow gastric emptying (GE). Whether human GE and appetite responses are regulated by the sweetness or bitterness per se of ingested food is, however, unknown. We aimed to determine whether intragastric infusion of "equisweet" (Study A) or "equibitter" (Study B) solutions slow GE to the same extent, and whether a glucose solution made sweeter by the addition of saccharin will slow GE more potently than glucose alone. Healthy nonobese subjects were studied in a single-blind, randomized fashion. Subjects received 500-ml intragastric infusions of predetermined equisweet solutions of glucose (560 mosmol/kgH(2)O), fructose (290 mosmol/kgH(2)O), aspartame (200 mg), and saccharin (50 mg); twice as sweet glucose + saccharin, water (volumetric control) (Study A); or equibitter solutions of quinine (0.198 mM), naringin (1 mM), or water (Study B). GE was evaluated using a [(13)C]acetate breath test, and hunger and fullness were scored using visual analog scales. In Study A, equisweet solutions did not empty similarly. Fructose, aspartame, and saccharin did not slow GE compared with water, but glucose did (P < 0.05). There was no additional effect of the sweeter glucose + saccharin solution (P > 0.05, compared with glucose alone). In Study B, neither bitter tastant slowed GE compared with water. None of the solutions modulated perceptions of hunger or fullness. We conclude that, in humans, the presence of sweetness and bitterness taste per se in ingested solutions does not appear to signal to influence GE or appetite perceptions.

Diabetic gastroparesis: diagnosis and management

Gastric emptying is frequently abnormal in patients with long-standing type 1 and type 2 diabetes mellitus. Symptoms commonly associated with disordered gastric emptying include nausea, vomiting, bloating and epigastric pain, while patients are also at risk of malnutrition, weight loss, impaired drug absorption, disordered glycaemic control and poor quality of life. Although often attributed to the presence of irreversible autonomic neuropathy, acute hyperglycaemia represents a potentially reversible cause of gastric dysfunction in diabetes. Scintigraphy represents the gold standard for measuring gastric emptying. The management of diabetic gastroparesis is less than optimal, partly because the pathogenesis has not been clearly defined. Treatment approaches include dietary modification and optimization of glycaemia, and the use of prokinetic drugs, while novel therapies such as gastric electrical stimulation are the subject of ongoing investigation.

Methods for the assessment of gastric emptying in critically ill, enterally fed adults

Critically ill patients may experience delayed gastric emptying. Patients receiving enteral feeding are monitored closely to detect a delay of gastric emptying, assess feeding tolerance, and prevent aspiration pneumonia. The most common practice for assessing gastric emptying is to measure the aspirated gastric residual volume; however, this is an unreliable method that lacks standardization, fails to differentiate normal digestive secretions from enteral formula, and results in unnecessary interruptions of enteral nutrition. The aim of this review is to identify an alternative method to assess gastric emptying, which should be reliable, sensitive, harmless, feasible, and inexpensive. Several techniques are discussed: scintigraphy, paracetamol absorption test, breath tests, refractometry, ultrasound, and gastric impedance monitoring. Refractometry seems to be the most appropriate tool for the regular assessment of enteral nutrition; however, standardization and validation of this method are needed before it can be routinely used to monitor critically ill patients receiving enteral nutrition.

Reliability of the time to maximal [13CO2] excretion and the half-[13CO2] excretion time as a gastric emptying parameter: assessments using the Wagner-Nelson method

In the [(13)C]-octanoate breath test, two popular parameters have been used to quantify gastric emptying rates, namely the time to the maximal [(13)CO(2)] excretion (T(max)) and the time to the half-[(13)CO(2)] recovery (T(1/2b)). Although each of T(max) and T(1/2b) is closely correlated with the scintigraphic half-emptying time, the two parameters occasionally indicate different judgments on a gastric emptying rate. In this study, to clarify which of the two parameters is more reliable, T(max) and T(1/2b) were compared to the "reference" parameters calculated using the Wagner-Nelson method, which allows accurate estimation of a time-course of gastric emptying from breath data. Ten healthy male volunteers underwent the breath test after ingestion of a muffin meal (320 kcal) containing 100 mg [(13)C]-octanoate. Breath samples were collected at 15-min intervals for 6 h. According to the conventional analytical algorithm, T(max) and T(1/2b) were mathematically calculated. By applying Wagner-Nelson analysis to the breath test, the time-percent gastric retention curve was generated and the half-emptying time (T(1/2WN)) was determined. T(1/2WN) was more closely correlated with T(max) (r=0.954, P<0.0001) than with T(1/2b) (r=0.782, P=0.008). T(max) was significantly correlated with the percent gastric retention value in the early (t=0.25 and 0.5 h), the middle (t=1.0 and 1.5 h), and the late (t=2.0 h) postprandial phase. T(1/2b) was significantly correlated with the gastric retention value in the middle and the late phase, but not with the gastric retention value in the early phase. The present results show that T(1/2b) has limited capability to reflect gastric emptying in the early postprandial period, suggesting that T(max) is more reliable than T(1/2b) as a gastric emptying parameter.

Effects of agar and pectin on gastric emptying and post-prandial glycaemic profiles in healthy human volunteers

1. Dietary fibre, such as pectin, delays gastric emptying and may enhance post-prandial glucose tolerance. Agar, which is high in fibre content, is widely used in the traditional Japanese diet. Although long-term diet therapy with agar decreases fasting plasma glucose levels in diabetes, knowledge is lacking about the acute effects of agar on gastric emptying and the post-prandial glycaemic profiles. The present study was designed to investigate the acute effects of agar. 2. Ten healthy male volunteers were studied on three occasions with three different test meals (450 kcal/500 mL): (i) a fibre-free meal; (ii) a meal with 2.0 g agar; or (iii) a meal with 5.2 g pectin. On each occasion, participants underwent a [(13)C]-acetate breath test along with serial blood sampling. To quantify gastric emptying, the half [(13)CO(2)] excretion time (t((1/2)b)) and the time for maximal [(13)CO(2)] excretion rate (t(lag)) were determined. The post-prandial glycaemic response was expressed as an incremental change from the fasting value at each sampling time. Data were analysed using repeated-measures analysis of variance (anova), followed by a post hoc paired Student's t-test with Bonferroni adjustment. 3. The time-course for respiratory [(13)CO(2)] excretion differed significantly among the three test meals (P = 0.0004, anova). Compared with the control meal, [(13)CO(2)] excretion was significantly lower following consumption of the agar meal (between 40 and 105 min post-prandially; P < 0.025, Student's t-test) and the pectin meal (between 40 and 180 min post-prandially; P < 0.025, Student's t-test). Among the three meals, significant differences were found in t((1/2)b) (P = 0.002, anova) and t(lag) (P = 0.011, anova). Compared with the control meal, the agar and pectin meals exhibited a significantly prolonged t((1/2)b) (P = 0.007 and P < 0.0001, respectively, Student's t-test) and t(lag) (P = 0.006 and P = 0.002, respectively, Student's t-test). Neither the agar nor pectin meal affected the post-prandial glucose profile. 4. In healthy adults, agar and pectin delay gastric emptying but have no impact on the post-prandial glucose response.

The Wagner-Nelson method makes the [13C]-breath test comparable to radioscintigraphy in measuring gastric emptying of a solid/liquid mixed meal in humans

1. Scintigraphy is the gold standard for measuring gastric emptying, but the use of radioactive isotopes can produce substantial irradiation. The [(13)C]-acetate/octanoic acid breath test is widely used as a non-radioactive alternative. 2. The half [(13)CO(2)] excretion time (T1/2b) is closely correlated with the scintigraphic half-emptying time (T1/2s). However T1/2b, is consistently remote from T1/2s, because the distribution of [(13)CO(2)] into the bicarbonate pool delays the respiratory excretion of the [(13)C] marker, which has already been emptied from the stomach. The time for the distribution process should be adjusted to diminish the discrepancy between the results of the scintigraphic and breath tests. 3. The Wagner-Nelson method provides an accurate profile of drug absorption. We have recently applied the Wagner-Nelson method to breath testing to adjust the time for [(13)CO(2)] distribution. In the present study, the [(13)C]-breath test with Wagner-Nelson analysis was compared with scintigraphy. 4. Six female volunteers simultaneously underwent scintigraphy and the breath test on two occasions, either to measure gastric emptying of the liquid phase (16 kcal) or for that of the solid phase (214 kcal). Time-percentage gastric retention curves were generated by scintigraphy and the breath test with Wagner-Nelson analysis. The half-emptying times were determined by interpolation from the scintigraphic curve (T1/2s) and the Wagner-Nelson curve (T1/2WN). T1/2b was calculated by conventional curve-fitting techniques. 5. For liquid and solid emptying, the gastric retention curves generated by the Wagner-Nelson method were comparable to the scintigraphic retention curves. For the liquid, T1/2b was significantly longer than T1/2s (93.8 +/- 7.3 vs 14.2 +/- 9.3 min, respectively; P < 0.0001), as was also observed for the solid phase (147.8 +/- 34.4 vs 35.3 +/- 11.2 min, respectively; P < 0.0001). In contrast, no significant differences were found between T1/2WN and T1/2s for the liquid (13.5 +/- 5.0 vs 14.2 +/- 9.3 min, respectively; P = 0.734) and the solid (45.8 +/- 10.2 vs 35.3 +/- 11.2 min, respectively; P = 0.051) phase. 6. In conclusion, Wagner-Nelson analysis makes the [(13)C]-breath test comparable to scintigraphy.