Theoretical flaws in the gastric emptying breath test: why is it dubious?

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 Kel=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 Kel=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 Kel=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 Kel=0.60 closely reflects measurements obtained with scintigraphy, whereas, in absolute terms, the conventional breath test analysis does not.

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.

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.

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

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

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

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

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.

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.

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.

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.

Rabeprazole delays gastric emptying of a nutrient liquid

BACKGROUND

It is generally considered that gastric acid suppression delays gastric emptying of solid meals because gastric hypoacidity impairs peptic digestion and antral triturition. Rabeprazole is one of the most potent acid suppressants. We conducted this cross-over study to investigate if rabeprazole delays gastric emptying of liquid nutrients, for which peptic digestion is unnecessary.

METHODS

On two randomized occasions, 13 healthy male volunteers underwent the (13)C-acetate breath test following ingestion of a 300 kcal-liquid meal. On one occasion, they had received 20 mg rabeprazole for the preceding 2 days and 1 h before the test. On another, they took no pretreatment. Based on 4 h breath samples, the half (13)CO(2) excretion time (t(1/2b)) and the time of maximal excretion (t(max)) were calculated as overall measures of gastric emptying. In addition, time profiles of gastric emptying were generated using the Wagner-Nelson analytical method, which creates the gastric emptying curve as accurately as the scintigraphy.

RESULTS

Rabeprazole significantly prolonged t(max) but unchanged t(1/2b). The gastric emptying profiles showed that rabeprazole evoked a segmental slowing of gastric emptying during 0.5-1.25 h of post-meal ingestion.

CONCLUSIONS

Rabeprazole suppresses gastric emptying of a liquid nutrient 0.5 h after meal ingestion. We have speculated that: (i) rabeprazole delays gastric emptying via a mechanism other than acid-pepsin maldigestion; and (ii) rabeprazole may intensify the post-gastric feedback regulation system (>0.5 h of post-meal).

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.

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.

Assessment of the gastric emptying velocity by the 13C-octanoate breath test: deconvolution versus a Wagner-Nelson analysis

BACKGROUND

The dynamic change in gastric emptying on a minute-by-minute basis (gastric velocity) is evaluated by the 13C-octanoate breath test with deconvolution analysis. However, deconvolution is impractical, because it requires dual experiments to obtain 13CO2 excretion profiles following intraduodenal and oral administration of 13C-octanoate. We investigated whether the Wagner-Nelson method, used in drug absorption studies, can determine the velocity profile based on a single experiment as accurately as deconvolution, and whether the velocity assessed by the Wagner-Nelson method is sensitive enough to detect subtle changes in gastric emptying induced by butylscopolamine.

METHODS

Five male volunteers underwent a 4-h breath test twice, after intraduodenal administration of 20 ml normal saline containing 100 mg 13C-octanoate and after ingestion of a 320-kcal muffin containing 100 mg 13C-octanoate. Deconvolution determined the velocity profile by subtracting duodenal from oral data, and the Wagner-Nelson method produced it from only oral data. The velocity profiles were compared between the two methods. Another six male subjects underwent the breath test by ingesting a muffin twice, once with and once without 20 mg oral butylscopolamine. The velocity profiles generated by the Wagner-Nelson analysis and the conventional 13CO2 excretion curves were compared between the two occasions.

RESULTS

The two techniques yielded identical velocity profiles. The velocity profile detected a significant change in the emptying pattern induced by butylscopolamine (initial acceleration with subsequent deceleration), while the conventional breath curves failed to detect this change.

CONCLUSIONS

Velocity assessment by a Wagner-Nelson analysis can precisely describe altered gastric emptying, based on a single experiment.

Measurement of gastric emptying by the 13C-octanoate breath test--rationalization with scintigraphy

The (13)C-octanoate breath test has not achieved universal acceptance for the measurement of solid phase gastric emptying, largely because the results are not comparable with those from direct methods such as scintigraphy. To convert breath-test data to their scintigraphic equivalent scale corrections are applied which have been obtained from population studies, but there is no guarantee that these are applicable in all cases. We propose an alternative method applicable on an individual basis based upon a simple physiological model which does not require any change to the breath-test protocol. It is demonstrated by comparison with scintigraphy and the octanoate saliva test. Results from an existing dataset of simultaneous breath test, saliva test and scintigraphic determinations of solid phase gastric emptying from nine healthy subjects were re-analysed. The corrected breath tests gave gastric emptying curves which were shown to be not significantly different to those obtained from scintigraphy. The method provides a simple but effective way of generating gastric emptying curves from breath-test data that are directly comparable with direct measurement methods, which is advantageous since it allows the whole of the gastric emptying profile to be generated, not just values for the lag phase and half-emptying times.

Measurement of gastric emptying by octanoate metabolism

PURPOSE OF REVIEW

Since its introduction just over 10 years ago, there have been a number of studies that have used the octanoate breath test to assess gastric emptying. Although use of the method is on the increase (the number of gastric emptying studies published on PubMed using the octanoate breath test has doubled between the periods 1997-2000 and 2001-2004 compared with a drop of approximately 20% in the use of scintigraphy over the same periods), the methodology has not achieved universal acceptance, primarily because it can provide results comparable to established techniques only indirectly.

RECENT FINDINGS

Recent methods for overcoming this difficulty are reviewed, including modified methods for breath test interpretation and the application of the related saliva test. The latter promises to be useful as a non-invasive proxy for established techniques, such as scintigraphy, for further validation of the breath test. Recent applications of octanoate-based methods are briefly considered.

SUMMARY

A novel approach detailed in this review for breath test interpretation, where the bicarbonate pool is modelled as a single compartment, could prove useful for obtaining breath test gastric emptying parameters that are directly comparable with those obtained from the gold standard, gamma scintigraphy. In combination with the saliva test, this could add credence to use of the octanoate breath test as a clinically accepted diagnostic tool, in addition to its potential in research.

WAGNER-NELSON METHOD FOR ANALYSING THE ATYPICAL DOUBLE-PEAKED [13CO2] EXCRETION CURVE IN THE [13C]-OCTANOATE GASTRIC EMPTYING BREATH TEST IN HUMANS

1. In the [(13)C]-octanoic acid breath test, the time versus pulmonary [(13)CO(2)] excretion rate curve is analysed using mathematical curve-fitting techniques to calculate gastric emptying parameters. Thus, the goodness-of-fit highly influences the accuracy of the breath test. However, a double-peaked [(13)CO(2)] excretion curve, which occasionally develops owing to the presence of an interval of quiescent gastric emptying (the plateau phase), is likely to be fitted poorly. 2. In pharmacokinetics, the Wagner-Nelson method has been used to describe precisely the absorption kinetics of orally administered drugs and its reliability is independent of the nature of gastric emptying. A recent study has shown the potential of the Wagner-Nelson method to generate a realistic gastric emptying flow curve from [(13)CO(2)] excretion data. In the present report, we have demonstrated that the Wagner-Nelson method can visualize the plateau emptying phase responsible for the cases of double peaks. 3. Wagner-Nelson analysis applied to the breath test described precisely the characteristic emptying pattern of the two emptying phases being interrupted by the plateau phase. Conventional analysis for the breath test failed to detect the plateau phase. 4. The Wagner-Nelson method is a useful tool for analysing atypical double-peaking [(13)CO(2)] excretion curves.

Effect of cigarette smoking on gastric emptying of solids in Japanese smokers: a crossover study using the 13C-octanoic acid breath test

BACKGROUND

Cigarette smoking is associated with an increased risk of peptic ulcer and gastroesophageal reflux disease. Gastric emptying disorders may play a role in the development of these upper gastrointestinal diseases. Thus, studies examining a link between smoking and gastric emptying disorders have clinical relevance. This study was conducted to investigate the effect of smoking on gastric emptying of solids in Japanese smokers.

METHODS

The (13)C-octanoic acid breath test was performed in eight male habitual smokers on two randomized occasions (either sham smoking or actively smoking). The time vs (13)CO(2) excretion rate curve was mathematically fitted to a conventional formula of y (t) = m*k*beta*e(-k*t)*(1 - e(-k*t))(beta-1), and the parameters of k and beta were determined: under the crossover protocol, a larger (smaller) beta indicates slower (faster) emptying in the early phase, and a larger (smaller) k indicates faster (slower) emptying in the later phase. The half (13)CO(2) excretion time (t(1/2b) = -[ln(1 - 2(-1/beta))]/k) and the time of maximal (13)CO(2) excretion rate (t(max) = [lnbeta]/k) were also calculated. Between the two occasions, k, beta, t(1/2b), and t(max) were compared by the Wilcoxon signed-rank test.

RESULTS

After smoking, k was significantly increased. No significant differences were found in beta, t(1/2), and t(max) between the two occasions.

CONCLUSIONS

The increase in k suggests the acceleration of gastric emptying in the later phase. For the first time, this study has revealed that acute smoking speeds the gastric emptying of solids in Japanese habitual smokers.