Impact of age, sex, race, and functional complaints on hydrogen (H2) production

Meta-Analysis of the Composition of Human Intestinal Gases

BACKGROUND

Understanding intestinal gases volume and composition may contribute to diagnosing digestive diseases and the microbiome's status. This meta-analysis aimed to define the composition of human intestinal gases and changes associated with diet.

METHODS

Studies were identified by systematic research of the MEDLINE(Ovid), Scopus, and Cochrane databases. Studies that measured the concentration of intestinal gases in healthy adult humans were retrieved. The JBI critical appraisal tool was used to evaluate the risk of bias. The primary outcomes analysed were the concentration of the most prevalent colonic gases. Participants were divided into groups according to dietary fibre content.

RESULTS

Eleven studies were included. The following gases were identified in similar concentrations across all studies (mean ± standard deviation): nitrogen (65.1 ± 20.89%), oxygen (2.3 ± 0.98%), carbon dioxide (9.9 ± 1.6%), hydrogen (2.9 ± 0.7%), and methane (14.4 ± 3.7%). Differences according to the dietary fibre were observed, with a positive correlation between fibre and volume of gas produced, particularly in fermented gases (carbon dioxide, hydrogen, and methane).

DISCUSSION

The meta-analysis has found defined concentrations of the five most common gases present in human colonic gas. Limitations included heterogenic methodologies, a low number of participants, and few recent studies. These findings may be helpful in diagnostic applications where colonic gas volume and composition are crucial factors, including functional disorders, microbiome analyses, and bowel perforation diagnostics.

Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition

Chronic diarrhoea is a common problem, hence clear guidance on investigations is required. This is an updated guideline from 2003 for the investigations of chronic diarrhoea commissioned by the Clinical Services and Standards Committee of the British Society of Gastroenterology (BSG). This document has undergone significant revision in content through input by 13 members of the Guideline Development Group (GDG) representing various institutions. The GRADE system was used to appraise the quality of evidence and grading of recommendations.

Genetic test for lactase non-persistence and hydrogen breath test: is genotype better than phenotype to diagnose lactose malabsorption?

BACKGROUND

Adult-type hypolactasia is a widespread condition throughout the world, causing lactose malabsorption. The lactose breath test is a simple tool for diagnosis but the need for prolonged monitoring of hydrogen excretion has led to a genetic test proposal. The aim of this study was to compare the genetic test with the lactose breath test in order to give some insights into the clinical value of genetic testing.

METHODS

Thirty-two consecutive functional patients underwent lactose breath test and lactase genetic polymorphism analysis (C/T 13910 and G/A 22018). Intolerance symptoms after lactose load were also monitored.

RESULTS

All patients with positive lactose breath test showed homozygosis for both polymorphisms. Among the nine patients with a negative breath test result, six showed heterozygosis while three showed homozygosis. Intolerance symptoms were present in 16 homozygotic patients but also in one heterozygotic patient. The k value for the agreement between the genetic test and the lactose breath test was 0.74.

CONCLUSION

A positive genetic test for lactase non-persistence indicates whether lactase activity decline may represent a clinical problem for the patient, but does not give information on actual patient symptoms. On the contrary, this information is already available by combining the lactose breath test with intolerance symptom evaluation. Lactose absorption phenotype may be not yet evident until young adult age.

Hydrogen breath testing versus LCT genotyping for the diagnosis of lactose intolerance: a matter of age?

BACKGROUND

Two single nucleotide polymorphisms (-13910 C/T and -22018 G/A) upstream of the lactase gene (LCT) have been found to be associated with lactose tolerance in Europeans.

METHODS

In one hundred and twenty Austrian outpatients, who visited the physician's office for symptoms of irritable bowel syndrome (IBS), hydrogen breath testing (HBT) and LCT genotyping by polymerase chain reaction and reverse-hybridisation were performed in parallel.

RESULTS

The coincidence between a genotype suggesting lactase non-persistence (lactose intolerance) and a positive HBT result was almost perfect (97.4% for LCT-13910 C/T and 100% for LCT-22018 G/A). Between a genotype indicating lactase persistence (lactose tolerance) and a negative HBT result the coincidence was lower (72% and 71.4%, respectively). Among heterozygotes, there was a statistically significant increase in the proportion of positive HBT results with age. Both SNPs were in accordance in 117/120 (97.5%) patients.

CONCLUSION

Genetic analysis of LCT-13910 C/T and LCT-22018 G/A is a good indicator for the presence of lactose intolerance. Because age, as well as a number of secondary causes (e.g. celiac disease), can influence HBT results, it is useful to combine HBT and genetic analysis in the diagnostic assessment of IBS.

Lactose digestion capacity in Tokelauans: a case for the role of gene flow and genetic drift in establishing the lactose absorption allele in a Polynesian population

Throughout the Pacific, lactose absorption occurs at rates of 0-46%. Most authors explain the current rate of lactose absorption in the Pacific in terms of gene flow with Europeans. However, researchers have not been able to determine the exact historical circumstances of the introduction of the lactose absorption gene. The availability of genealogical material, historical information, and mal/absorption frequencies for Tokelau (a Polynesian population) presents a unique opportunity to examine the role of gene flow in establishing lactose absorption in Pacific isolates. In an earlier study, Cheer and Allen ([1997] Am. J. Hum. Biol. 93:1-34) determined lactose digestion capacities for 58 Tokelauans. In the current study, we constructed pedigrees for the same 58 individuals, using the Tokelau Island Migrant Study genealogies (Wessen et al. [1992]). Results indicated that 8 of 13 lactose-absorbing individuals have European ancestors, compared with only 4 of 35 lactose malabsorbers (Chi(2) = 15.75, P < 0.01). Six lactose-absorbing individuals have either American or Portuguese ancestors dating back to the mid-1800s. Historical data were used to establish the contribution of Portuguese and American genetic material to the Tokelau population following massive depopulation after the Peruvian slave raids of 1863. This study provides clear evidence for the role of a population bottleneck followed by gene flow and genetic drift in establishing lactose absorption in the Tokelau population. Furthermore, it is the first study of a Pacific population to directly link lactose absorption with gene flow.

Lactose intolerance

Lactose maldigestion has been under intensive research since its discovery in the 1960's. We know the prevalence of lactose maldigestion in a great number of countries and ethnic groups. However, there is often no provision made for the secondary type of maldigestion, and the study populations have sometimes been selected rather than picked at random. New methods for the measurement of lactose digestion have been developed, and its genetic mechanisms have received a great deal of attention during the last few years. However, in many studies the measurement and/or reporting of symptoms has quite often been overlooked. In this review, various topics related to lactose intolerance are discussed with a special emphasis on its symptoms.

No inhibition of gastro-intestinal propulsion after propofol- or propofol/ketamine-N2O/O2 anaesthesia. A comparison of gastro-caecal transit after isoflurane anaesthesia

BACKGROUND

Gastrointestinal motility may be considerably reduced by anaesthesia and or surgery resulting in postoperative ileus. Inhibition of propulsive gut motility is especially marked after an opioid-based technique. Little, however, is known of the gastrointestinal effects of the hypnotic propofol when given continuously over a longer period of time, which is the case in total intravenous anaesthesia (TIVA) and in intensive care sedation. We therefore set out to study the effects of a propofol-based nitrous oxide/oxygen anaesthesia (group PO) on gastro-caecal transit time. The results were compared with a propofol-ketamine technique (group PK) and an isoflurane-based anaesthesia (group I; each group n = 20).

METHODS

Gastro-caecal transit was determined by measurement of endexpiratory hydrogen concentration (ppm). Following gastral installation of lactulose at the end of the operation, the disaccharide was degraded by bacteria in the caecum, resulting in the liberation of hydrogen which was expired. A 100% increase in endexpiratory hydrogen concentration compared to the preinduction period was considered the end-point of gastro-caecal transit.

RESULTS

There was no significant difference with regard to gastro-caecal transit in the three groups of patients. In the propofol group mean gastro-caecal transit was 119 (+/- 50.6 SD) min, in the propofol-ketamine group it was 147 (+/- 57.4 SD) min, and in the isoflurane group transit time was 122 (+/- 48.6 SD) min.

CONCLUSION

The data suggest that propofol, even when given as a continuous infusion, does not alter gastrointestinal tract motility more than a standard isoflurane anaesthesia. The data may be particularly relevant to patients who are likely to develop postoperative ileus. They also suggest that in an ICU setting propofol does not alter gut motility more than a sedation technique with the analgesic ketamine.

D-xylose hydrogen breath tests compared to absorption kinetics in human patients with and without malabsorption

The D-xylose breath H2 test may be useful in characterizing intestinal absorptive function. Our aim was to determine whether breath H2 following D-xylose administration reflects the extent to which the D-xylose is absorbed by comparing it to a kinetic model of D-xylose absorption. Twenty-five subjects were studied. They ingested 15 g D-xylose on the first day and 25 g D-xylose on the third day. On the second day they received 10 g intravenous D-xylose along with 15 g oral lactulose. Multiple serum and urine samples were obtained for D-xylose content to calculate its rate constants and extent of absorption by multicompartmental analysis. Breath H2 determinations were obtained every 15 min for 3 hr following the 15 g D-xylose and lactulose ingestion. Peak breath H2 concentration correlated with extent of absorption (r = -0.787, P < 0.001), K0, the rate constant for nonabsorptive loss (r = 0.744, P < 0.001), and 5-hr urine content (r = -0.705, P < 0.001). Area under the breath H2 curve also correlated with these parameters: extent of absorption (r = -0.770, P < 0.001), K0 (r = 0.662, P < 0.001), 5-hr urine content (r = -0.629, P < 0.012). Peak D-xylose breath H2 to peak lactulose breath H2 showed no correlation with extent of absorption. The extent of absorption was higher with the 15-g dose than the 25-g dose in all patients tested (P < 0.01). (ABSTRACT TRANCATED AT 250 WORDS)

The effect of aging on oro-cecal transit time in normal subjects and patients with gallstone disease

To ascertain whether aging and/or cholelithiasis can influence oro-cecal transit time (OCTT), we studied a total of 70 subjects, i.e., 10 healthy young adult controls, 22 healthy elderly controls, 18 elderly cholelithiasis patients and 20 elderly subjects with a history of cholecystectomy for gallstones. OCTT was measured by means of the hydrogen breath test after administering a liquid meal of 10 g of lactulose in 200 mL of water, and collecting exhaled breath samples every 10 minutes for 200 minutes. Of all subjects in the group of patients with a history of cholecystectomy, 6/20 were non-hydrogen producers, and therefore were not included in the study. The OCTT was found to be significantly longer in healthy elderly controls, than in healthy young adult controls; the elderly subjects who had undergone cholecystectomy had a longer OCTT than the healthy elderly controls, while no difference was detected when compared to elderly patients with gallstones. In conclusion, OCTT seems to increase in healthy aging. Cholecystectomy also increases OCTT in the elderly, suggesting a link between intestinal motility and the biliary tract which may be of pathophysiological significance.

Detection of malabsorption of low doses of carbohydrate: accuracy of various breath H2 criteria

BACKGROUND

Although the accuracy of breath H2 testing to detect malabsorption of small (< 50 g) doses of carbohydrate has never been evaluated, studies suggest that its accuracy is limited by a high prevalence of "H2 nonproducers." The aim of this study was to determine the accuracy of H2 breath testing in the detection of malabsorption of 10 g of carbohydrate.

METHODS

In 55 healthy subjects, we determined the ability of breath H2 measurements to distinguish between the ingestion of 10 g of a nonabsorbable carbohydrate (lactulose) and two control meals, a nonabsorbable electrolyte solution or glucose (10 g).

RESULTS

The conventional criterion of a 20 ppm increase in breath H2 had 100% specificity but failed to identify lactulose malabsorption in 47% and 24% of subjects at 4 and 8 hours of testing. In contrast, a breath H2 of > 6 ppm at 5 or 6 hours had near perfect specificity and sensitivity. A sum of breath H2 at 5, 6, and 7 hours of > 15 ppm yielded perfect separation between lactulose and control solutions.

CONCLUSIONS

True "H2 nonproducers" are extremely rare. Using appropriate criteria, breath H2 testing provides a very accurate means of identifying malabsorption of low doses of carbohydrate.

Prevalence and consistency of low breath H2 excretion following lactulose ingestion. Possible implications for the clinical use of the H2 breath test

The clinical use of the H2 breath test is limited by the finding that a variable fraction of the population fails to excrete appreciable H2 during colonic carbohydrate fermentation. Therefore, we assessed the ability to increase breath H2 excretion in 371 patients (224 female, 147 male) by administering the nonabsorbable sugar lactulose. Following 12g of lactulose, 27% of 94 patients did not increase their breath H2 concentration over 20 ppm and were considered low H2 excretors. Ingestion of 20 g of lactulose in 277 patients yielded a frequency of low H2 excretors of 14%. Six of 10 patients that were low H2 excretors after 12g of lactulose increased their breath H2 levels over 20 ppm when tested with 20g. In 35 patients tested with the same amount of lactulose on two separate occasions, the subject frequently altered his or her H2 producing status over a period of a few weeks. Low H2 excretors had a significantly higher breath CH4 concentration, both fasting (22 +/- 34 ppm) and after lactulose (51 +/- 58 ppm) compared to the remaining patients (5 +/- 13 ppm and 16 +/- 40 ppm, respectively). While the mean age of low excretors (54 +/- 17 years) was significantly higher than the others (44 +/- 17 years), no difference was found for sex prevalence and stool pH. This study demonstrates that respiratory H2 excretion following lactulose ingestion is not consistent and suggests that the application of too restrictive criteria could lead to improper interpretation of the H2 breath test.

Symptom provocation in irritable bowel syndrome. Effects of differing doses of fructose-sorbitol

The role of fructose and sorbitol, when ingested together, in the aetiology of irritable bowel syndrome (IBS) is controversial. The aims of this study in IBS patients, therefore, were to compare differences in symptom provocation with various doses of fructose-sorbitol and to relate differences in the extent of colonic hydrogen production after each dose to such symptom provocation. Two different mixtures of fructose and sorbitol--20 g fructose plus 3.5 g sorbitol ('lower' dose) and 25 g fructose plus 5 g sorbitol ('higher' dose)--were administered to 15 patients with IBS and to 24 healthy controls. Breath hydrogen concentrations were determined at 10-min intervals for 3 h after ingestion of each mixture, and the presence and severity of a range of gastrointestinal symptoms were recorded on a standard form before, during, and after the study. Total symptom score in IBS patients, but not controls, was greater (p < 0.05) after the higher than after the lower dose of fructose-sorbitol mixture, and, for the higher dose, symptoms were significantly greater in IBS patients than in controls (p < 0.05). Moreover, the increase in total symptom score between the higher and lower dose mixtures was of a greater magnitude (p = 0.01) in IBS patients than in controls. No significant correlation was observed between the increase in symptom score and the increase in peak hydrogen concentration or the increase in integrated hydrogen response between lower and higher dose mixtures, although these latter increases were at times substantial.(ABSTRACT TRUNCATED AT 250 WORDS)

Combustible colonic gas levels during flexible sigmoidoscopy and colonoscopy

To what extent the standard preparation for sigmoidoscopy (phosphosoda enemas) makes the bowel safe for electrocautery is unknown. Sixty patients were prospectively evaluated to compare the presence of the combustible gases hydrogen and methane during colonoscopy and flexible sigmoidoscopy. Thirty patients underwent flexible sigmoidoscopy after phosphosoda enema preparation, and 30 patients underwent colonoscopy after a polyethylene glycol solution preparation. During colonoscopy, the concentrations of hydrogen and methane remained below combustible levels in all patients. Even segments of colon with significant fecal matter present did not have combustible levels of these two gases. However, at flexible sigmoidoscopy, combustible levels of hydrogen and methane were measured in 3 of 30 (10%) patients. Due to the risk of explosion, electrocautery should not be performed during routine flexible sigmoidoscopy after the standard phosphosoda enema preparation.

Reproducibility of measurements of trace gas concentrations in expired air

Measurement of the pulmonary excretion of trace gases has been used as a simple means of assessing metabolic reactions. End alveolar trace gas concentration, rather than excretory rate, is usually measured. However, the reproducibility of this measurement has received little attention. In 17 healthy subjects, duplicate collections of alveolar air were obtained within 1 minute of each other using a commercially available alveolar air sampler. The concentrations of hydrogen, methane, carbon monoxide, and carbon dioxide were measured. When the subject received no instruction on how to expire into the device, a difference of 28% +/- 19% (1SD) was found between duplicate determinations of hydrogen. Instructing the subjects to avoid hyperventilation or to inspire maximally and exhale immediately resulted in only minor reduction in variability. However, a maximal inspiration held for 15 seconds before exhalation reduced the difference to a mean of 9.6% +/- 8.0%, less than half that observed with the other expiratory techniques. Percentage difference of methane measurements with the four different expiratory techniques yielded results comparable to those obtained for hydrogen. In contrast, percentage differences for carbon monoxide measurements were similar for all expiratory techniques. When normalized to a PCO2 of 5%, the variability of hydrogen measurements with the breath-holding technique was reduced to 6.8% +/- 4.7%, a value significantly lower than that obtained with the other expiratory methods. This study suggests that attention to the expiratory technique could improve the accuracy of tests using breath hydrogen measurements.