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Black-Box Gastrointestinal Tract-Needs and Prospects of Gaining Insights of Fate of Fat, Protein, and Starch in Case of Exocrine Pancreatic Insufficiency by Using Fistulated Pigs. Nutrients 2017; 9:nu9020150. [PMID: 28212351 PMCID: PMC5331581 DOI: 10.3390/nu9020150] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 02/13/2017] [Indexed: 11/16/2022] Open
Abstract
Exocrine pancreatic insufficiency (EPI) results in the maldigestion and malabsorption of nutrients. The digestive processes in humans and other monogastric species like rat and pig are characterized by a predominantly enzymatic digestion within the small intestine and microbial fermentation located in the hindgut. For protein, it is doctrine that only prececally absorbed amino acids can be transferred to the amino acid pool of the host, while postileal absorption of nitrogen-containing compounds occurs mainly in the form of ammonia, being a burden rather than a benefit for the organism. The pig is an established animal model for humans to study digestive processes. As digestion is markedly impaired in case of EPI the use of an appropriate animal model to study the effects of this disease and to optimize treatment and dietetic measures is of special interest. By using an animal model of experimentally-induced EPI allowing differentiating between digestive processes in the small as well as in the large intestine by use of ileo-cecal fistulated animals, marked effects of EPI on prececal digestion of starch and protein could be shown. The data indicatethat estimation of digestibility of nutrients over the entire digestive tract results in a distinct overestimation of enzymatic digestion of starch and protein. Therefore, this model clearly shows that protein and starch digestion are significantly reduced in case of EPI although this cannot be detected on a fecal level. As postileal fermentation of starch is associated not only with energy losses but also with intensive gas production, this is of special interest to minimize meteorism and improve wellbeing of patients.
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Gregory PC, Hoffmann K, Kamphues J, Möeler A. The Pancreatic Duct Ligated (Mini)pig as a Model for Pancreatic Exocrine Insufficiency in Man. Pancreas 2016; 45:1213-26. [PMID: 27623555 DOI: 10.1097/mpa.0000000000000674] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Modern therapy of pancreatic exocrine insufficiency (PEI) using pancreatic enzyme replacement therapy (PERT) has largely been very effective and has greatly helped in improving the nutritional status of patients with PEI and in increasing the life expectancy in cystic fibrosis. It is believed that the use of predictable large animal models could play an important role in assessing and developing new therapies. This article reviews the pancreatic duct ligated (adult) minipig as a chronic model of total PEI, with a detailed look at the influence of PEI and response to PERT on prececal compared to fecal digestibility, to directly investigate effects on protein and starch digestion and absorption. In addition, the piglet with PEI is reviewed as a model for PEI in young patients with the aim of further improving the therapy and nutritional status of young patients with cystic fibrosis.
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Affiliation(s)
- Peter Colin Gregory
- From the *Abbott Laboratories GmbH; and †Institute for Animal Nutrition, University of Veterinary Medicine Hannover, Foundation, Hannover, Germany
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3
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Atteinte digestive (pancréatique et intestinale) de la mucoviscidose : approche physiopathologique. Arch Pediatr 2012; 19 Suppl 1:S20-2. [DOI: 10.1016/s0929-693x(12)71103-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Abstract
The present study was aimed to improve and simplify the 13C-mixed TAG (13C-MTG) breath test while keeping it acceptable for the patient. Healthy volunteers (ten women and eight men) were examined on four occasions, receiving in a random order 300 mg 13C-MTG: (1) contained in two wafers; (2) administered with a 50 g wheat roll; as well as given with either (3) 10 or (4) 30 g butter, spread onto a 50 g wheat roll, as the test meal, respectively. Samples of expiratory air were taken for 6 h postprandially for the mass spectroscopic measurement of 13CO2 enrichment. After intake of the sole 13C-MTG, the cumulative 13C recovery in breath air (AUC) appeared to be unsatisfactory, as after 6 h it did not exceed 10 %. Application of the substrate with the 50 g wheat roll did not bring about any improvement in this parameter. The addition of the unlabelled fat to the test meal dramatically increased the cumulative 13C recovery. However, we found higher values for the momentary 13C recovery and AUC with 10 g butter compared with 30 g. It can be concluded that: (1) addition of unlabelled fat is indispensable to obtain a proper course of the breath 13C elimination during the conduct of the 13C-MTG breath test and (2) it is possible to apply a considerably smaller amount of the unlabelled fat than has previously been recommended for this test.
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Barclay AR, Morrison DJ, Weaver LT. What is the role of the metabolic activity of the gut microbiota in inflammatory bowel disease? Probing for answers with stable isotopes. J Pediatr Gastroenterol Nutr 2008; 46:486-95. [PMID: 18493202 DOI: 10.1097/mpg.0b013e3181615b3a] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The pathogenesis of inflammatory bowel disease remains obscure. However, there has been increasing interest in the role of the gut microbiota, focusing in particular on the "unculturable majority" of luminal and mucosal bacteria, which until recently have been difficult to study owing to the technical challenges of identification and elucidating function. Bacterial components and metabolites have been implicated in signalling to host immune systems and regulating inflammatory responses. Although the rapid expansion in techniques of molecular microbiology has increased our understanding of bacterial diversity, the tools to assess bacterial metabolic activity, and to link the 2, lag behind. Stable isotope probing is a powerful technique to link the metabolic activity and diversity of "unculturable" bacteria through isotopic labelling of biomarkers such as DNA and RNA. Progression of current stable isotope probing methodology with high-resolution oligonucleotide 16s rRNA probe technology and high precision liquid chromatographic isotope ratio mass spectrometry may facilitate application in human microbial ecology. Progress towards stable isotope probing use in vivo, in concert with other advances in bacterial metabolome analysis, will lead to the development of a dynamic picture of the metabolic activity and diversity of intestinal bacteria in inflammatory bowel disease. Such insights will, over time, lead to fuller understanding of inflammatory bowel disease pathogenesis and the development of targeted therapies to reverse the "dysbiosis" that precedes disease relapse.
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Affiliation(s)
- Andrew R Barclay
- Department of Child Health, Division of Developmental Medicine, University of Glasgow, UK.
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Braden B, Lembcke B, Kuker W, Caspary WF. 13C-breath tests: current state of the art and future directions. Dig Liver Dis 2007; 39:795-805. [PMID: 17652042 DOI: 10.1016/j.dld.2007.06.012] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2007] [Revised: 06/14/2007] [Accepted: 06/28/2007] [Indexed: 12/11/2022]
Abstract
13C-breath tests provide a non-invasive diagnostic method with high patient acceptance. In vivo, human and also bacterial enzyme activities, organ functions and transport processes can be assessed semiquantitatively using breath tests. As the samples can directly be analysed using non-dispersive isotope selective infrared spectrometers or sent to analytical centres by normal mail breath tests can be easily performed also in primary care settings. The 13C-urea breath test which detects a Helicobacter pylori infection of the stomach is the most prominent application of stable isotopes. Determination of gastric emptying using test meals labelled with 13C-octanoic or 13C-acetic acid provide reliable results compared to scintigraphy. The clinical use of 13C-breath tests for the diagnosis of exocrine pancreatic insufficiency is still limited due to expensive substrates and long test periods with many samples. However, the quantification of liver function using hepatically metabolised 13C-substrates is clinically helpful in special indications. The stable isotope technique presents an elegant, non-invasive diagnostic tool promising further options of clinical applications. This review is aimed at providing an overview on the relevant clinical applications of 13C-breath tests.
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Affiliation(s)
- B Braden
- John Radcliffe Hospital, Headley Way, OX3 9DU Oxford, UK.
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Fridge JL, Conrad C, Gerson L, Castillo RO, Cox K. Risk factors for small bowel bacterial overgrowth in cystic fibrosis. J Pediatr Gastroenterol Nutr 2007; 44:212-8. [PMID: 17255834 DOI: 10.1097/mpg.0b013e31802c0ceb] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
OBJECTIVES The purpose of this study was to determine the prevalence of small bowel bacterial overgrowth in patients with pancreatic-insufficient cystic fibrosis (CF) compared with age-matched controls and to identify potential risk factors for small bowel bacterial overgrowth. PATIENTS AND METHODS Fifty patients, 25 pancreatic-insufficient CF study patients (mean age, 17 y) and 25 gastrointestinal clinic control patients (mean age, 15 y), completed a glucose-hydrogen breath test after an overnight fast. Study patients completed a quality-of-life questionnaire modified from the Cystic Fibrosis Questionnaire. The medical history of each patient was compared with breath test results. A positive breath test was defined as a fasting hydrogen > or =15 ppm or a rise of > or =10 ppm hydrogen over baseline during the test. RESULTS The prevalence of positive breath tests was higher in the CF study group (56%) than in the control group (20%) (P = 0.02). The mean fasting hydrogen levels of patients in the study and control groups were 22 and 5 ppm (P = 0.0001). The mean questionnaire scores were not significantly different between breath test-positive and -negative study patients. The use of azithromycin was associated with an increased risk of a positive breath test. Use of laxatives and inhaled ipratropium was associated with a decreased risk of a positive breath test. CONCLUSIONS Patients with CF were more likely to have elevated fasting hydrogen levels compared with controls. This suggests a high prevalence of small bowel bacterial overgrowth in CF patients. Medications commonly used by CF patients may influence intestinal health.
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Affiliation(s)
- Jacqueline L Fridge
- Division of Gastroenterology, Children's Hospital and Research Center Oakland, Oakland, CA 94609-1809, USA.
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Zhong L, Furne JK, Levitt MD. An extract of black, green, and mulberry teas causes malabsorption of carbohydrate but not of triacylglycerol in healthy volunteers. Am J Clin Nutr 2006; 84:551-5. [PMID: 16960168 DOI: 10.1093/ajcn/84.3.551] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND In vitro studies suggest that extracts of black, green, and mulberry teas could interfere with carbohydrate and triacylglycerol absorption via their ability to inhibit alpha-amylase, alpha-glucosidase, sodium-glucose transporters, and pancreatic lipase. OBJECTIVE We measured breath hydrogen and 13CO2 to investigate the ability of an extract of black, green, and mulberry tea leaves to induce malabsorption of carbohydrate and triacylglycerol in healthy volunteers. DESIGN In a crossover design, healthy adult volunteers randomly ingested test meals with a placebo beverage or a preparation containing an extract of black (0.1 g), green (0.1 g), and mulberry (1.0 g) teas. One test meal contained 50 g carbohydrate as white rice, 10 g butter, and 0.2 g [13C]triolein, and the beverages contained 10 g sucrose. The calorie content of the second test meal consisted entirely of lipid (30 g olive oil and 0.2 g [13C]triolein). Breath-hydrogen and 13CO2 concentrations were assessed hourly for 8 h, and symptoms were rated on a linear scale. RESULTS With the carbohydrate-containing meal, the tea extract resulted in a highly significant increase in breath-hydrogen concentrations, which indicated appreciable carbohydrate malabsorption. A comparison of hydrogen excretion after the carbohydrate-containing meal with that after the nonabsorbable disaccharide lactulose suggested that the tea extract induced malabsorption of 25% of the carbohydrate. The tea extract did not cause triacylglycerol malabsorption or any significant increase in symptoms. CONCLUSION This study provides the basis for additional experiments to determine whether the tea extract has clinical utility for the treatment of obesity or diabetes.
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Affiliation(s)
- Litao Zhong
- NatureGen Inc, San Diego, CA, Minneapolis, MN 55417, USA
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Stellaard F, Elzinga H. Analytical techniques in biomedical stable isotope applications: (isotope ratio) mass spectrometry or infrared spectrometry? ISOTOPES IN ENVIRONMENTAL AND HEALTH STUDIES 2005; 41:345-61. [PMID: 16543190 DOI: 10.1080/10256010500384333] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
An overview is presented of biomedical applications of stable isotopes in general, but mainly focused on the activities of the Center for Liver, Digestive and Metabolic Diseases of the University Medical Center Groningen. The aims of metabolic studies in the areas of glucose, fat, cholesterol and protein metabolism are briefly explained, as well as the principle of breath testing and the techniques to study body composition and energy expenditure. Much attention is paid to the analytical considerations based upon metabolite concentrations, sample size restrictions, the availability of stable isotope labelled substrates and dose requirements in relation to compound-specific isotope analysis. The instrumental advantages and limitations of the generally used techniques gas chromatography/reaction/isotope ratio mass spectrometry and gas chromatography/mass spectrometry are described as well as the novelties of the recently commercialised liquid chromatography/combustion/isotope ratio mass spectrometry. The present use and future perspective of infrared (IR) spectrometry for clinical and biomedical stable isotope applications are reviewed. In this respect, the analytical demands on IR spectrometry are discussed to enable replacement of isotope ratio mass spectrometry by IR spectrometry, in particular, for the purpose of compound-specific isotope ratio analysis in biological matrices.
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Affiliation(s)
- Frans Stellaard
- Laboratory of Pediatrics, Center for Liver, Digestive and Metabolic Diseases, University Hospital Groningen, Hanzeplein 1, 9713 GZ, Groningen, The Netherlands.
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Jonderko K, Kasicka-Jonderko A, Syrkiewicz-Trepiak D, Błońska-Fajfrowska B. Feasibility of a breath test with a substrate of natural 13C-abundance and isotope-selective non-dispersive infrared spectrometry: a preliminary study. J Gastroenterol Hepatol 2005; 20:1228-34. [PMID: 16048571 DOI: 10.1111/j.1440-1746.2005.03920.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
Abstract
BACKGROUND AND AIMS Isotope-selective non-dispersive infrared spectrometry (NDIRS) is a cheaper alternative to isotope ratio mass spectrometry (IRMS). We checked on the efficiency of NDIRS to perform a breath test with naturally (13)C-enriched maize starch. METHODS Fifty-six healthy volunteers were examined. After a basal fasted sample of their expiratory air was collected, the subjects ate a test breakfast of 50 g (CF50 group, n = 9) or 100 g (CF100 group, n = 47) cornflakes with 175 g yoghurt. For 6 h thereafter, exhaled air was collected every 30 min for the NDIRS measurement of (13)CO(2) concentration. RESULTS The time-course of the curves of (13)CO(2) concentration resembled those obtained previously with IRMS. A dose-response to the amount of ingested cornflakes was observed--the maximum postprandial net increment in (13)CO(2) was statistically significantly higher in the CF100 than CF50 group: 4.78 +/- 0.13 versus 3.12 +/- 0.17 per thousand (P < 0.001), whereas the time needed to reach the maximum did not differ after the intake of 50 g (233 +/- 13 min) or 100 g (248 +/- 9 min) cornflakes. The 5-h area-under-the-curve of cumulative (13)CO(2) net recovery (AUC(60-360)) was statistically significantly greater after ingestion of 100 g compared to 50 g cornflakes (97.6 +/- 2.2 versus 61.7 +/- 2.2 micromol, P < 0.001) and it also exhibited a stable between-subject variability. CONCLUSION The obtained proof of technical feasibility of a breath test with the use of naturally (13)C-enriched starch and NDIRS provides background for future research on the clinical usefulness of this method for a non-invasive assessment of the pancreatic exocrine function.
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Affiliation(s)
- Krzysztof Jonderko
- Department of Basic Biomedical Science, School of Pharmacy, Medical University of Silesia, PL-41-205 Sosnowiec, Poland.
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Kalnins D, Corey M, Ellis L, Durie PR, Pencharz PB. Combining unprotected pancreatic enzymes with pH-sensitive enteric-coated microspheres does not improve nutrient digestion in patients with cystic fibrosis. J Pediatr 2005; 146:489-93. [PMID: 15812451 DOI: 10.1016/j.jpeds.2004.10.063] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
OBJECTIVES To assess the efficacy of combining unprotected powder enzymes and oral enteric-coated microsphere (ECM) and to ECM alone in treating nutrient maldigestion in patients with cystic fibrosis. STUDY DESIGN Patients were randomly assigned into 2 consecutive, 2-week phases; ECM alone, and ECM plus unprotected powder enzymes. Fecal fat, energy, and nitrogen output were compared with intake at the end of each phase. Two-tailed, paired t tests were performed to compare outcomes. RESULTS The mean age of the 14 patients (3 girls) was 5.7 +/- 3.2 years (range, 1.9 to 13.4 years). There was no significant difference in percent malabsorption of fat (15.6% vs 18.2%), energy (13.3% vs 13.4%), or nitrogen (11.8% vs 11.3%) between phases. CONCLUSIONS The addition of powder enzymes to ECM did not improve nutrient maldigestion compared with ECM alone.
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Affiliation(s)
- Daina Kalnins
- Division of Respiratory Medicine, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8
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Symonds EL, Kritas S, Omari TI, Butler RN. A combined 13CO2/H2 breath test can be used to assess starch digestion and fermentation in humans. J Nutr 2004; 134:1193-6. [PMID: 15113969 DOI: 10.1093/jn/134.5.1193] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Ingestion of starch from corn (naturally enriched with (13)C) should produce (13)CO(2) after small intestinal digestion and (13)CO(2) and H(2) from colonic fermentation. This study used a combined (13)CO(2)/H(2) breath test to assess the digestion and fermentation of resistant starch and to show that the test could detect changes in digestibility due to cooking. Volunteers consumed 40 g digestible cornstarch with water (n = 8), or 40 g resistant cornstarch in liquid (n = 12) or cooked into a pancake (n = 4). Interval breath sampling was performed and analyzed for (13)CO(2) and H(2). Ingestion of resistant starch produced a double-peaked (13)CO(2) excretion curve. The first increase in (13)CO(2) occurred at the same time as excretion from digestible starch (55 +/- 9 and 68 +/- 9 min, respectively), which was due to small intestinal digestion. The second increase in (13)CO(2) was accompanied by an increase in H(2) excretion (432 +/- 15 and 428 +/- 48 min, respectively), which was indicative of colonic bacterial fermentation. Cooking resistant starch increased its degree of digestion from 36 to 72%. The (13)CO(2)/H(2) breath test can be used to estimate digestion and fermentation of starches in different physiologic and pathologic conditions.
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Affiliation(s)
- Erin L Symonds
- Gastroenterology Unit, Women's and Children's Hospital, North Adelaide, and Department of Physiology, University of Adelaide, Adelaide, South Australia.
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Ritz MA, Fraser RJ, Di Matteo AC, Greville H, Butler R, Cmielewski P, Davidson G. Evaluation of the 13C-triolein breath test for fat malabsorption in adult patients with cystic fibrosis. J Gastroenterol Hepatol 2004; 19:448-53. [PMID: 15012784 DOI: 10.1111/j.1440-1746.2003.03310.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
Abstract
BACKGROUND AND AIMS A simple non-invasive test not requiring the use of radioactive isotopes is required to assess fat malabsorption in adult cystic fibrosis (CF) patients. Breath tests using substrates labeled with 13C meet these conditions. The 14C-triolein breath test is sensitive and specific for measuring fat malabsorption, but involves radiation exposure. The aim of this study was to examine the utility of a test using a 13C label and to determine whether pancreatic replacement therapy would return the test to the values of a normal control group. METHODS 13CO2 recovery was assessed after an overnight fast in six adult patients with CF, both with and without pancreatic enzyme replacement therapy (PERT) in the usual dose for a light snack, in a randomized order, on different days. Studies were also performed in eight healthy volunteers after oral ingestion. Subjects drank 50 mL of a liquid meal mixed with 200 microL 13C-triolein and breath samples were collected by blowing through a straw into collection tubes every 30 min for 6 h. The effect of gastric emptying was assessed by comparison of oral ingestion with intraduodenal infusion. Intra-individual variability was assessed in nine volunteers by repeating the breath test after drinking the test meal on a separate day. RESULTS Compared with healthy subjects there was virtually no recovery of 13CO2 in CF patients without PERT. The median (interquartile range) cumulative percentage dose recovery (cPDR) at 6 h was 3% (0-8) in CF patients compared with 28% (22-41) in healthy controls (P < 0.01). Fat absorption was normalized (37%) (36-43) after ingestion of PERT. Gastric emptying delayed the peak in 13CO2 recovery, but there was no difference in the cPDR at 6 h. There was no difference in recovery between days 1 and 2. CONCLUSIONS The 13C-triolein breath test is a simple and reproducible method to measure fat malabsorption. The test provides a screening technique for fat malabsorption in adult CF patients and may be useful for monitoring the lowest effective dose of PERT.
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Affiliation(s)
- Marc A Ritz
- Gastrointestinal Unit, Royal Adelaide Hospital, Adelaide, South Australia, Australia
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Christian MT, Amarri S, Franchini F, Preston T, Morrison DJ, Dodson B, Edwards CA, Weaver LT. Modeling 13C breath curves to determine site and extent of starch digestion and fermentation in infants. J Pediatr Gastroenterol Nutr 2002; 34:158-64. [PMID: 11840033 DOI: 10.1097/00005176-200202000-00010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
BACKGROUND The colon salvages energy from starch, especially when the capacity of the small intestine to digest it is limited. The aim of this study was to determine the site and relative extent of starch digestion and fermentation in infants. METHODS Thirteen infants (10 male and 3 female infants), median age 11.8 months (range, 7.6-22.7 months), were fed a starchy breakfast containing 13C-labeled wheat flour after an overnight fast. Duplicate breath samples were obtained before breakfast and every 30 minutes for 12 hours. Breath 13CO2 enrichment was measured using isotope ratio mass spectrometry, and results were expressed as percentage dose recovered (PDR) for each 30 minutes. The PDR data were analyzed and mathematically modeled assuming either a constant estimate of CO2 production rate or adjusted for physical activity. RESULTS Mean +/- SD cumulative 13C PDR (cPDR) at 12 hours was 21.3% +/- 8.4% for unadjusted data and 26.5% +/- 11.6% for adjusted data. A composite model of two curves fit significantly better than a single curve. Modeling allowed estimation of cPDRs of small intestine (17.5% +/- 6.5% and 22.7% +/- 9.3% for unadjusted and adjusted data, respectively) and colon (4.6% +/- 2.9% and 6.3% +/- 5.4%). CONCLUSIONS Modeling of 13CO2 enrichment curves after ingestion of 13C-enriched wheat flour is an attractive means to estimate the contribution of the upper and lower gut to starch digestion and fermentation.
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