Measurement of gastric emptying by octanoate metabolism

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

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

Development and validation of a gas chromatography-mass spectrometry method to analyze octanoate enrichments at low concentrations in human plasma

A new method for accurately analyzing octanoate enrichment in plasma was developed and validated. Samples were derivatized directly in plasma by transesterification with isobutanol and were analyzed by gas chromatography-mass spectrometry (GC-MS). This method was developed to analyze the precursor enrichment in a stable isotope tracer protocol. Glyceryl tri[1,2,3,4-¹³C₄] octanoate, a stable isotope-labeled medium-chain triglyceride (MCT), was orally administered in combination with (1) exclusively MCT or (2) a combination of protein, carbohydrates, and MCT to investigate the metabolic route of oral MCT under various conditions. Accurate analysis of octanoate enrichment in plasma at concentrations as low as 0.43 μM (lower limit of quantification, LLOQ) was performed. This is an improvement of about twenty times for the LLOQ for analysis of the enrichment of octanoate when compared with the gold-standard method for fatty acid analysis (methyl esterification). Moreover, we found that' with this gold-standard method, study samples were easily contaminated with (unlabeled) octanoate from other sources, leading to biased, incorrect results. The precision and linearity obtained using the new method were good (coefficient of variation intraday < 9.1%, interday < 9.3%, R² of the calibration curve > 0.99). The sensitivity was sufficient for analyzing samples obtained using the stable isotope protocol. This new method is more sensitive than methyl esterification and it minimizes the risk of contamination. Graphical abstract.

Acid-base changes after fluid bolus: sodium chloride vs. sodium octanoate

Objectives

This study aims to test the hypothesis that fluid loading with sodium chloride (150 mmol Na and 150 mmol Cl) or sodium octanoate (150 mmol Na, 100 mmol Cl, and 50 mmol octanoate) would lead to different acid–base changes.

Design

We performed a double-blind crossover experimental study.

Setting

The study was done at a University Physiology Laboratory.

Subjects

Eight Merino ewes were used as subjects.

Measurements and main results

We randomly assigned animals to a rapid intravenous infusion (1 L over 30 min) of either normal saline (NS) or sodium octanoate solution (OS). We collected blood samples at 0.5, 1, 2, 4, and 6 h after the start of the infusion for blood gas analyses and biochemistry. We calculated strong ion difference apparent (SIDa), effective strong ion difference, and strong ion gap (SIG). Animals in the NS group developed metabolic acidification immediately after fluid administration (pH 7.49 to 7.42, base excess 3.0 to -1.6 mEq/L), while the OS group did not (pH 7.47 to 7.51, base excess 1.1 to 1.4 mEq/L; P < 0.001). Additionally, the OS group had higher SIDa (36.2 vs. 33.2 mEq/L) and SIG (7.4 vs. 6.2 mEq/L) at the end of the infusion.

Conclusions

Our findings provide further evidence that acidification induced by intravenous fluid loading is dependent on fluid composition and challenges the paradigm of the so-called dilutional acidosis.

Electronic supplementary material

The online version of this article (doi:10.1186/2197-425X-1-4) contains supplementary material, which is available to authorized users.

Dyspeptic symptoms and delayed gastric emptying of solids in patients with inactive Crohn's disease

Background

Patients with Crohn’s disease (CD) have been shown to present dyspeptic symptoms more frequently than the general population. Some of these symptoms could be related to motility disorders to some degree. Then, we propose to investigate whether gastric emptying of solids in patients with inactive CD is delayed and to determine the relationships between gastric emptying and dyspeptic symptoms in inactive CD.

Methods

Twenty-six patients with inactive Crohn’s disease, as defined by a Crohn’s Disease Activity Index (CDAI) < 150, underwent a gastric emptying test by breath test using ¹³C octanoic acid coupled to a solid meal and answered a validated questionnaire (The Porto Alegre Dyspeptic Symptoms Questionnaire) to assess dyspeptic symptoms. Patients with scores ≥ 6 were considered to have dyspepsia. The control group was composed by 19 age- and sex-matched healthy volunteers.

Results

Patients with CD had a significantly longer t 1/2 and t lag (p<0.05) than the controls. CD patients with dyspepsia had significantly (p<0.05) prolonged gastric emptying when compared to patients without dyspeptic symptoms. When the individual symptom patterns were analyzed, only vomiting was significantly associated with delayed gastric emptying (p<0.05). There was no difference between the subgroups of patients with respect to gender, CDAI scores, disease location, clinical behavior (obstructive/obstructive) or previous gastrointestinal surgery.

Conclusion

Delayed gastric emptying in inactive Crohn’s disease patients seems to be associated with dyspeptic symptoms, particularly vomiting, even without any evidence of gastrointestinal obstruction.

Effects of postgastric 13C-acetate processing on measurement of gastric emptying: a systematic investigation in health

Uniform postgastric processing of the gastric emptying (GE) marker 13C-acetate (Ac) is an unverified assumption behind its widespread application to measure GE. This study assessed the postgastric processing of Ac administered by intraduodenal (i.d.) infusion simulating different physiological conditions. 13CO2 in breath was assessed in three groups of six volunteers after i.d. administration of A: Different caloric densities (0.75/1.5/3 kcal min(-1) in a 200 mL meal at constant 1 mg Ac min(-1) simulating a physiological range of nutrient delivery rates; B: different tracer delivery rates (0.5/1.0/2.5 mg Ac min(-1) simulating delayed, normal and increased GE; C1: a 500 mL meal resulting in same marker and caloric delivery compared to protocol A; C2: 50 mL water bolus injections of 12.5/25/50/100 mg Ac and C3 bolus injections of 50 mg Ac in 50/100/200 mL water in randomized order. A: 13CO2 excretion was independent of caloric load (P = 0.59). B: The dynamic of 13CO2 excretion was modulated by tracer elimination which was in turn dependent on the speed of tracer delivery, i.e. with faster deliveries resulting in lower 13CO2 recovery during infusion (P < 0.001). C: Increasing Ac doses resulted in decreased 13CO2 recovery (P < 0.001) over the first hour. 13CO2 recovery kinetics was independent of the volume delivered. This study shows 13C-acetate absorption and metabolism is independent of the volume and caloric delivery of test meals. The 'lag' in estimates of GE derived from 13CO2 breath tests is due to a postgastric, dose-dependent delay to 13CO2 elimination. This can be corrected for in analytical derivations of GE parameters based on 13C-acetate breath test measurements.

The stable isotope ketoisocaproic acid breath test as a measure of hepatic decarboxylation capacity: a quantitative analysis in normal subjects after oral and intravenous administration

BACKGROUND AND AIMS

There is no generally accepted kinetic evaluation method for the stable isotope [(13)C]ketoisocaproic acid (KIC) breath test. Differences found in the results between women and men are contradictory.

METHODS

Oral and intravenous breath tests using 1 mg/kg stable isotope-labelled KIC were performed in healthy male and female volunteers. A power exponential function was fitted to the mass spectrometric data of breath (13)CO(2) enrichment, allowing mathematical analysis of time-to-peak-excretion, half-excretion time, percent label recovery and parameters describing the shape of the curve. Body composition was determined using bioelectrical impedance analysis.

RESULTS

After oral administration, total label recovery after 3 h was about 22% and was not different between men (n=7) and women (n=8). The time to maximal label excretion was 0.67 +/- 0.12 h in men and 0.9 +/- 0.32 h in women (P=0.028) and the excretion curve showed an initially slower rise in women compared with men. Adjusting for lean body mass or body water abrogated the sex differences. Total label recovery after intravenous administration was about 9%, suggesting that the substrate was rapidly catabolized in the muscle compartment after intravenous administration.

CONCLUSIONS

The modified power exponential function described allows standardized estimates of the KIC breath test results. When corrected for body composition, there are no differences in breath test results between men and women. The comparison between oral and intravenous results provides robust evidence that the KIC breath test measures predominantly hepatic and not muscle decarboxylation and is thus a highly specific liver function test.

Recent advances in the interpretation of the (13)C octanoate breath test for gastric emptying

The (13)C octanoate breath test for gastric emptying has still not achieved its full potential in clinical practice, largely because of uncertainty in how to relate its results to those of more established techniques, such as gamma scintigraphy. Here we briefly review the test and then go on to discuss recent advances in its validation and interpretation.

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.

Effect of a cellulose-containing weight-loss supplement on gastric emptying and sensory functions

CM3, a highly cross-linked cellulose in capsule form, expands in the stomach to a size several fold of its original volume. It is purported to induce a prolonged feeling of satiation and a delay in gastric emptying, thus promoting weight loss. We examined whether CM3 delays gastric emptying (using the stable isotope (13)C-octanoic breath test) and whether it influences subjective feelings of appetite sensations (using visual analog scales, VASs). We performed a double-blind randomized placebo-controlled crossover trial in 19 moderately obese but otherwise healthy subjects (mean age 55 +/- 9 years, BMI 31.1 +/- 4.6 kg/m(2)). The subjects were treated with six capsules of CM3 or matching placebo 30 min before a standardized solid meal. Breath collection and VASs were performed over 4 h every 15 min and 30 min, respectively. Half-excretion time of (13)CO(2) in breath, indicating gastric emptying half time, was the primary outcome parameter. The study was powered to detect a change in gastric emptying of 20-30 min. Mean (13)CO(2) half-excretion time changed from 2.3 +/- 0.4 to 2.4 +/- 0.33 h (mean difference +6 min, 95% confidence interval (CI) -3 to +15 min; P = 0.17). Appetite sensations (hunger, satiation, fullness, prospective food consumption, desire to eat something sweet, salty, savory, or fatty) changed over time during the course of the postprandial phase but were not influenced by CM3 (repeated measures ANOVA). In obese subjects, acute administration of the weight-loss supplement CM3 does not delay gastric emptying and does not influence subjective appetite sensations.

Retention, fixation, and loss of the [13C] label: a review for the understanding of gastric emptying breath tests

A [13C]-breath test is a promising method for measuring gastric emptying. The methodological relevance is based on a close correspondence between gastric emptying of [13C]-acetate/octanoate (input) and pulmonary excretion of [13CO2] (output). Despite the close input-output correspondence, the pulmonary output is quite remote from the gastric input: the pulmonary output is delayed compared to the gastric input, and the total recovery of [13CO2] in the breath is incomplete. This review focuses on the kinetics of [13C]-acetate/octanoate in the body and suggests that (1) the delayed pulmonary output results from temporal retention of [13CO2] in the well-perfused tissues (heart, brain, etc.), (2) the incomplete recovery results from incorporation of the label into metabolic products (ketone bodies, amino acids, etc.) or from fixation of [13CO2] in the low-perfused tissues (bone, skeletal muscle, etc.), and (3) knowledge on the retention is the key to appropriate interpretations of breath test results. Recognition of these kinetic aspects is essential for appropriate interpretations of these breath test results.

Frequent feeding delays the gastric emptying of a subsequent meal

To assess the suitability of the 13C-octanoic acid breath test for measuring gastric emptying in circumstances other than the post-absorptive state, a preliminary study was performed where 6 hourly spaced isoenergetic meals preceded the determination of gastric emptying of a subsequent 2 MJ meal. Emptying was measured in three individuals on four separate occasions, with a reproducibility of 8%. A crossover study was then conducted to test the hypothesis that meal frequency can modulate the gastric emptying of a subsequent meal, with the potential to influence appetite regulation. Sixteen subjects were fed to energy balance, receiving food either as 2 isoenergetic meals 3 h apart or 6 isoenergetic meals fed hourly. Gastric emptying of a subsequent 2 MJ meal was investigated. Visual analogue scales were used throughout to assess appetite. The maximum rate of gastric emptying was unchanged but the onset of emptying was delayed by the more frequent feeding pattern. There was no significant difference in subjective appetite before or after the test meal. In conclusion, short-term increases in feeding frequency delayed the gastric emptying of a subsequent meal, but significant effects on post-meal appetite could not be demonstrated.

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

1. The [(13)C]-acetate breath test (ABT) quantifies gastric emptying as the half [(13)CO(2)]-excretion time (T(1/2b)), but T(1/2b) differs from the scintigraphic half-emptying time (T(1/2s)). The aims of the present study were to accurately determine the half-emptying time by ABT with Wagner-Nelson analysis (T(1/2WN)), to compare T(1/2WN) with T(1/2s) and to validate the Wagner-Nelson strategy in ABT. 2. For a comparative study, eight volunteers simultaneously underwent ABT and scintigraphy. Anterior images were acquired and breath samples were collected every 15 min for 4.0 h after ingestion of a 200 kcal liquid meal labelled with 37 MBq [(99m)Tc]-colloidal sulphur and 100 mg [(13)C]-acetate. For the validation experiment, another six volunteers underwent ABT, on two randomized occasions, using the 200 kcal liquid meal with 100 mg [(13)C]-acetate. On either of the two occasions, a gel-forming agent was stirred into the meal to intentionally delay gastric emptying by increasing meal viscosity. Breath samples were collected at regular 15 min intervals for 4 h post ingestion. 3. The Wagner-Nelson equation for ABT is F(t) = (A(breath)(t) + C(t)/0.65)/A(breath)(infinity), where F(t) is a fractional dose of the [(13)C] label emptied, C(t) is the [(13)CO(2)] excretion (% dose/h), A(breath)(t) is the area under the C(t) curve (% dose) and A(breath)(infinity) is the ultimate [(13)CO(2)] recovery in breath (% dose). The percentage gastric retention was estimated as 100 x (1 - F(t)). The time plots of scintigraphic activity and 100 x (1 - F(t)) were fitted to y(t) = 100 x e(-Kxt), K values were estimated mathematically for each plot by regression analysis and T(1/2s) and T(1/2WN) were calculated as (ln2)/K. The time versus pulmonary [(13)CO(2)] excretion plots were fitted to z(t) = m x k x beta x e(-kt)(1 - e(-kxt))(beta-1), where m, k and beta are constants; T(1/2b) was calculated as -(ln(1 - 2(-1/beta))]/k. 4. Values of T(1/2WN) were closer to T(1/2s) than T(1/2b), although T(1/2WN) and T(1/2b) yielded significant under- and overestimation of T(1/2s), respectively. The high viscosity meal significantly prolonged T(1/2WN) and T(1/2b); T(1/2WN) could detect the delayed transit of the viscous meal more sensitively than T(1/2b). 5. The Wagner-Nelson method improves the accuracy of the ABT.