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Keywords:

  • gastric accommodation;
  • SPECT;
  • barostat;
  • MRI;
  • ultrasound;
  • nutrient drink test

Abstract

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Abstract Gastric accommodation is considered important in the pathophysiology of several upper gastrointestinal disorders including functional dyspepsia. The gold standard for its measurement is the barostat-balloon study which requires intubation. The aim was explore the reliability and performance characteristics of the techniques proposed for measurement of gastric accommodation. We undertook a literature search using MEDLINE with a broad range of key words. The accommodation reflex and its control are briefly described, based on human data. The performance characteristics of the intragastric barostat, transabdominal ultrasound, magnetic resonance imaging, single photon emission computed tomography, and satiation drinking tests are described. For each technique, we summarize the following: principle, validation studies, advantages, disadvantages, and potential applications. Three-dimensional methods to measure gastric volume non-invasively are promising and among the best validated to date. Simpler techniques would be of considerable appeal for clinical and research studies, but further validation is necessary before satiation drinking tests can be used as surrogates for more sophisticated measurements of gastric accommodation.


Introduction

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In the last 2 decades, a wide array of research techniques to evaluate gastric motility and sensation has been introduced. Some are currently applied in clinical practice, e.g. electrogastrography, manometry and scintigraphic gastric emptying.1 No single test currently available is capable of measuring all parameters of gastric motility simultaneously (gastric emptying, gastric accommodation, antral motility).

Because of reports of an association between dyspeptic symptoms and reduced gastric accommodation, there is a growing interest in measuring the accommodation reflex: the gastric barostat technique was the first method and it is generally regarded as the gold standard for quantifying gastric post-prandial relaxation. However, the invasive nature of this procedure makes its use in clinical practice limited. Thus, a comfortable yet sensitive and reproducible alternative is needed.

Several volumetric imaging techniques [ultrasound, magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT)] and two non-imaging assessments (satiety drinking test, water load test) have been proposed. This paper reviews these techniques and their potential in research and clinical practice. Advantages, validation experiments to date, drawbacks and pitfalls will be discussed through a critical objective review of literature.

Review methodology

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The authors undertook a search using Medline using the following search words: accommodation, barostat, stomach relaxation, stomach volume, gastric sensation, nutrient drink test, water load test, satiety, satiation, and the combinations: SPECT and stomach, MRI and stomach. The results of the studies whose primary aim was to validate and to describe the performance of the individual techniques are reported. In addition, data from selected papers assessing gastric accommodation within the protocol of drug trials are shown whenever these data added information on the validity of the testing techniques to measure gastric accommodation.

The accommodation reflex: definition and physiology

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Gastric accommodation is a vagally mediated reflex that occurs post-prandially, results in reduction of tone, and provides a reservoir for the meal. This relaxation allows ingestion of a considerable volume load without a significant rise of intragastric pressure or induction of upper gastrointestinal symptoms such as distension, bloating, early satiety or vomiting. Relaxation mainly involves the proximal stomach region. However, volume increase also occurs in the distal stomach.2

The reflex can be triggered by nutrient infusion in the oropharynx, stomach or small intestine.3 The accommodation reflex has two components: receptive relaxation, which occurs within seconds of gastric distension and is possibly inducible by oropharyngeal stimulation alone, and adaptive relaxation, a slower response that may be modulated by specific nutrients.4 Although the two phases of the response may be physiologically separate, a standard accommodation response, as recorded by gastric barostat or imaging methods, does not differentiate these two phases. The factors controlling food-induced relaxation are incompletely understood. Even simple questions such as the relationship of the magnitude of the response to different caloric densities, or to different composition or different volumes of equicaloric meals are unanswered.

The physiology of the accommodation response has been extensively studied in animal models5,6 and in humans. It involves a vagovagal reflex pathway influencing the balance maintained by cholinergic excitatory drive and non-adrenergic non-cholinergic (NANC) inhibitory input. The afferent signal is generated by activation of stretch-sensitive mechanoreceptors in the stomach wall and by activation of osmo- and chemo-receptors in the stomach and duodenum.7 This stimulus activates a vagovagal reflex loop. The efferent NANC signal has been proved to involve nitric oxide (NO) as a principal transmitter at the neuromuscular junction.8,9 Co-transmission by vasoactive intestinal polypeptide (VIP) was suggested but never demonstrated by means of experiments with VIP agonists or antagonists10 in humans.

Gastric tone is also modulated by sympathetic stimuli: a direct effect modulated by post-junctional α1-adrenoceptors on non-sphincter smooth muscle, and an indirect effect on cholinergic nerve terminals mediated by pre-junctional α2-adrenoceptors. A study examining the effect of clonidine (α2-agonist) and nitroglycerin (NO donor) as monitored by intragastric barostat balloon (Fig. 1) has shown that both nitrergic and sympathetic stimuli modulate the accommodation response.11 Similarly, by using l-NMMA to inhibit nitrergic mechanisms,12 others demonstrated the importance of NO in mediating gastric relaxation.

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Figure 1. Relaxatory effect of clonidine and nitroglycerin on proximal gastric tone compared with placebo in the fasting period and the preserved accommodation response after meal ingestion. Tracings obtained using gastric barostat technique (Reproduced with permission from Ref. 11).

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A link from gastric accommodation to functional dyspepsia

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Why should gastric accommodation be evaluated? Impaired gastric accommodation has been associated with upper gastrointestinal symptoms including early satiety, bloating, epigastric pain, weight loss, nausea, functional (or non-ulcer) dyspepsia,13,14 diabetic gastroparesis, 15 rumination syndrome,16 and prior surgery including fundoplication,17 vagotomy and partial gastrectomy.18

This impaired response was extensively studied in up to 40% of cases of functional dyspepsia.13,19,20 Other pathophysiological findings in this disorder are delayed gastric emptying, visceral hypersensitivity, abnormal gastroduodenal coordination and central nervous system (CNS) dysfunction. A technique that allows measurement of gastric accommodation with sufficient validity, sensitivity and reliability would be very useful in the evaluation of patients with endoscopy-negative upper gut symptoms.

Measurement of the reflex response to feeding

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The following techniques will be discussed: intragastric barostat bag technique, imaging tests such as abdominal ultrasound, MRI and SPECT, and non-imaging methods, specifically satiety/nutrient drinking and water load tests.

Intragastric barostat studies

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This method is regarded as the gold standard to which all other techniques need to be compared for validation. Due to patient discomfort and special expertise required, this method never impacted clinical practice except in a few academic, tertiary centres.

Principle

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This involves transesophageal introduction of a polyethylene balloon, compliant up to 1.0–1.2 L, in the gastric fundus. The balloon is connected to a barostat device via a double-lumen polyvinyl tube and is distended until an intrabag volume of 30 mL is reached19,21 or until respiratory variation is noted.18 This implies that the balloon is in apposition with the gastric wall and reflects movement of the diaphragm. This pressure is known as the minimal distending pressure (MDP). Arbitrarily, MDP + 1 mmHg is accepted as the baseline pressure. Other groups arbitrarily apply 2 mmHg above the pressure at which respiratory variation is first recorded. The barostat keeps the balloon in apposition with the gastric wall, and it allows isobaric volume fluctuation of the balloon. Volumes can thus be measured as the intraballoon pressure fluctuates with changes in gastric tone.

Validating studies

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To prove that the procedure is reliable, Tack et al. tested the reproducibility of the volume response measured on two separate occasions in health and dyspepsia.22 The results were evaluated using the Bland–Altman method (Fig. 2). This is a very useful and important study, and the only one published to date. It addresses reproducibility of barostat measurements of gastric accommodation post-meal. Nevertheless, there are some pitfalls in the interpretation of the results, which are worthy of further discussion.

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Figure 2. Bland–Altman plot, comparing the difference of measurements recorded on two separate occasions with the mean of the two measurements. Individual data for nine healthy subjects and 13 dyspeptics are presented. Coefficient of variation was 19% (4) and 43% (12) for healthy controls and dyspeptic subjects, respectively (Reproduced with permission from Ref. 22). Reproducibility is considered significant if the scatter (quantified by the standard deviation SD) of the differences in volume response remains limited (small SD).

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The plot (Fig. 2) reveals an intra-individual mean difference of approximately 100 mL, which is considerable given the fact that the median relaxation in disease is approximately 140 mL in this cohort22 and 190 ± 24 mL in other publications from the same authors.19 In addition, the plot presents no cut-off value to determine whether the intra-individual deviation (scatter) is significant and acceptable for clinical use.

The reported inter-individual coefficient of variation is greater in dyspepsia compared with controls, but this difference in coefficient is mainly due to the volume difference for these two groups, whereas the scatter remains just as large in the dyspepsia group and the control group (Fig. 2). Therefore, the reproducibility of the barostat test is actually not very favourable for intra- or inter-individual studies. The sample size needed for a study using this technique is fairly large. In fact, assuming a standard deviation of 75 mL, the number of patients per group referred to show a 25% difference in accommodation response (25% of 190 = 45 mL) is 45 per group for a parallel group study and 24 for a cross-over study.

Another way of developing and validating a test is to determine if it can distinguish normal from disease state with sufficient power, or to demonstrate results that would be predicted for certain perturbations. For gastric accommodation, this can be shown by comparing data from healthy controls and dyspeptic patients. Mearin et al.23 were among the first to study the accommodation reflex in health vs dyspepsia. They found no difference in compliance between the two groups. Tack et al. successfully demonstrated a significant decrease of the volume response for dyspeptics (n = 40) compared with controls (190 ± 24 mL vs 337 ± 18 mL).19 Note the pooled standard deviation for patients and controls is approximately 140 mL, and the difference in post-meal volume in the two groups was 147 mL. In contrast to Mearin et al., Tack et al. had sufficient power to detect the change in volume in 40 dyspepsia patients relative to 35 controls. Post-hoc sample sizes required were 16 per group.

With regard to pharmacological perturbations, the barostat technique has revealed predictable results (e.g. Tack et al. proved that l-NMMA impairs accommodation12 and Thumshirn et al. demonstrated the involvement of nitrergic and adrenergic factors by means of clonidine and nitroglycerin).11

Advantages

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The gastric barostat is still the reference method for quantifying gastric accommodation in response to a meal. It has been extensively used and validated by demonstration of effects of disease and perturbations in numerous protocols at many tertiary referral centres. However, reliability is relatively poor.

Disadvantages

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The technique is invasive and uncomfortable or stressful for many subjects, and this may bias measurements of tone and sensation. The lack of consistent reproducibility is a pitfall in interpreting barostat study results. The balloon may alter intragastric distribution of the meal; the direct stimulus imposed by the balloon itself on the stomach wall results in exaggeration of antral relaxation.24

Transabdominal ultrasound studies

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Ultrasonography has already been used to record gastric emptying,25 antral motility and transpyloric flow.26 Its usefulness for measuring the accommodation reflex is under investigation.27

Principle

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Conventional ultrasonographic imaging is employed to measure two sections of the stomach area: one section in a sagittal plane is used to calculate proximal gastric area (PGA, Fig. 3A); and a second section in an oblique frontal plain provides the proximal gastric diameter (PGD, Fig. 3B). According to the authors, multiplying the parameters gives a geometric estimate of proximal gastric volume (PGA × PGD = aV).27 Comparing fasting and post-prandial measurements allows indirect measurement of the accommodation response.

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Figure 3. Ultrasound sections used to estimate proximal gastric volume. (A) Proximal gastric area measured in a sagittal plane (area from top fundus margin to 7 cm aborad). (B) Proximal gastric diameter in a frontal oblique plain (maximal diameter in this section) (reproduced with permission from Ref. 27).

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Validating studies

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In a first protocol, inter- and intra-observer agreement were evaluated for quantifying PGA and PGD after ingestion of a mixed liquid meal.27 The Bland–Altman analysis showed moderate day-to-day variation. Correlation coefficients were 0.91 (PGA) and 0.84 (PGD) for the inter-observer agreement; 0.96 (PGA) and 0.74 (PGD) for intra-observer agreement. Day-to-day variation of the method was estimated as the coefficient of variation of all measurements and ranged between 0.06 and 0.18.

The method has been used to document impaired accommodation in functional dyspepsia and diabetes. In dyspepsia, both the PGA and the PGD were abnormal in patients compared with controls.28 In diabetes, there was a significant difference relative to controls only in the PGA dimension.29

The effect of pharmacological perturbations and comparison with the results expected from previous literature were tested with sumatriptan (a 5-HT1-receptor agonist), a substance known to relax the gastric fundus.19 Sumatriptan increased gastric measurements of PGA and PGD.30 It should be stressed that no data comparing ultrasound measurements to barostat are available. None of the papers provide plots of the approximate volume (aV =PGA×PGD).

Advantages

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The technique is potentially widely available as ultrasound is applied in different disciplines of medicine. It is inexpensive, non-invasive, and does not involve the use of harmful material or ionizing radiation. Simultaneous assessment of gastric emptying, antral motor function, transpyloric flow and gastric accommodation is possible.

Disadvantages

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Technical difficulties are presented by intragastric gas and anatomic obstructions (costal margin) that narrow the image window. The technique requires experience and is highly user-dependent. Guided three-dimensional imaging of gastric emptying is described in the literature, but evaluation of accommodation remains to be validated.31,32

Potential applications

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Reliability and accuracy of the method need further evaluation before implementation in a clinical setting would be appropriate. Further studies are mandatory and need to be cross-validated by other centres.

Magnetic resonance imaging

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This safe and very accurate technique is able to image the entire stomach with great detail. Theoretically, it should be possible to assess several gastric properties in one investigation (anatomy, gastric emptying, gastric motility, secretion, intragastric meal distribution).

Principle

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After ingestion of a test meal labelled with gadolinium as an MRI marker, images of the stomach region are acquired, typically using a Spin Echo T1-weighted imaging sequence. The inherent characteristics of the MRI technique allow three-dimensional reconstruction of the stomach, enabling total gastric volume measurements during fasting and post-prandially. The ratio of these measurements quantifies the accommodation response.

Validation studies

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While several papers have documented use of MRI to measure intragastric dilution and emptying33,34 or intragastric distribution of medication and gastric emptying,35–37 none of the studies has assessed MRI for measuring gastric accommodation.

One paper by de Zwart et al. compares assessment of gastric volume during fasting with MRI or barostat measurement, but fails to investigate the volume response of the stomach post-prandially.38 Moreover, as also shown with SPECT, the volumes measured with the two techniques differ significantly as the barostat measures only the proximal stomach whereas MRI records entire stomach volume. The volumes correlate well (P < 0.05). MRI was also able to record volume effects induced by glucagon (known to relax the stomach) and erythromycin (known to contract the stomach) (Fig. 4). Studies on the accommodation response after food ingestion are eagerly awaited.

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Figure 4. Dynamic alterations in intragastric volume over time as assessed with MR (solid line) and the barostat (dashed line), effect of glucagon (relaxes the stomach) and erythromycin (contracts the stomach) (reproduced with permission from Ref. 38).

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Advantages

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The MRI technique is safe, non-invasive and does not involve the use of ionizing radiation. Images have high resolution and three-dimensional reconstruction is possible. Simultaneous assessment of multiple parameters of gastric physiology is possible (anatomy, motility, intragastric distribution, secretion).

Disadvantages

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The MRI equipment is still not widely available for GI investigators. The cost of imaging is very high and imaging in an upright position is possible only in very few centres. However, preliminary MRI data suggest that there is no difference in the measurement of gastric relaxation in response to a liquid and solid meal between the sitting and the left lateral decubitus positions.39

Potential applications

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This method seems very promising and is patient-friendly. Nevertheless, reliability and validity of the method in health and disease need further testing before MRI can be considered a useful tool to measure gastric accommodation.

Single photon emission computed tomography

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The use of 99mTc imaging in gastroenterology is well known (e.g. for the diagnosis of Meckel's diverticula, a congenital malformation containing ectopic gastric mucosal tissue). This application is based on the unique capability of both parietal (oxyntic) and non-parietal (mucous) cells to take up and excrete 99mTc-pertechnetate from the circulating blood pool.40 The use of SPECT to quantify the gastric accommodation response was first proposed and further validated by the Mayo group.

Principle

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After intravenous administration of the pertechnetate radiomarker in a dose of 10–20 mCi, tomographic images in an axial plane are acquired using a large field-of-view dual-head gamma camera system. Three-dimensional reconstruction of data is performed using commercially available computer software (Analyze PC 2.5). Measuring total gastric volume during fasting and post-prandial periods enables an estimation of the accommodation response to food ingestion (expressed as volume difference or as volume ratio).

Validating studies

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As producing the three-dimensional images requires the observer to manually remove any extraneous structures that had not been removed by the software system (e.g. upper duodenum, kidneys), intra- and inter-observer reproducibility were tested.2 For observer reproducibility, the CVinter was 13% during fasting and 12% post-prandially; CVintra was 9% during fasting and 8% post-prandially. These results indicate that the analysis technique, rather than the test itself, is reproducible.

Comparison of SPECT data with barostat was performed after ingestion of a liquid test meal (Ensure®, Ross, Columbus, OH, USA).21 As expected and also demonstrated with MRI, total gastric volumes measured by SPECT were larger than intragastric volumes obtained by the barostat bag, which only documents proximal stomach volume changes. Mean volumes of post-prandial to fasting volumes measured by SPECT and barostat, respectively, were highly comparable (P = 0.6; R2 = 0.7) (Fig. 5).

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Figure 5. Correlation of post-prandial accommodation ratios, as measured by SPECT (reproduced with permission from Ref. 21).

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In order to assess whether SPECT is able to distinguish normal from abnormal, Kim et al. compared gastric volume post-prandial to fasting ratios from healthy controls with ratios from patients with idiopathic non-ulcer dyspepsia.41 The results indicated that 41% of the patients had an impaired volume response to food ingestion, the same proportion as evidenced by Tack et al. using the barostat.19 The experiment showed that post-prandial volumes exceeded the fasting volumes plus the 300 mL meal by mean values of 300 mL in controls and 210 mL in dyspeptic subjects, allowing the stomach to accommodate the meal, swallowed air and gastric secretions. Overall, the dyspeptic group had significantly lower post-prandial volume changes (P < 0.001 for the post-prandial to fasting ratio).

Similar experiments were performed for impaired accommodation post-fundoplication, yielding significantly lower accommodation ratios compared with healthy controls (P < 0.003).21 This was, in part, due to higher fasting gastric volumes relative to controls (P < 0.005). These results were extended to other groups (e.g. diabetes, rumination syndrome) in a recent publication of 214 patients.20

In order to evaluate whether SPECT is capable of confirming pharmacological perturbations of gastric motor function as predicted from previous literature, a protocol was developed to evaluate the effects of i.v. erythromycin (increases proximal gastric tone) and sublingual isosorbide dinitrate (NO donor, relaxes proximal stomach).42 Isosorbide relaxed fasting stomach volume compared with controls (P < 0.05), but there was no significant difference post-prandially (plateau effect: maximum relaxation was already obtained after the meal). Erythromycin reduced the post-prandial volume response (P < 0.05) but had no significant effect on the fasting volume (floor effect). Delgado-Aros et al. used SPECT to illustrate the relaxing effect of glucagon-like peptide 1 (GLP-1) on the gastric fundus,43 as Schirra et al. had already demonstrated using the barostat method.44

Advantages

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Single photon emission computed tomography allows three-dimensional imaging of the stomach, enabling measurement of total gastric volume. Data on large numbers of male and female adult volunteers have been provided in the literature.21 The method has systematically been proved to be sensitive, and the procedure is non-invasive. Reproducibility is the subject of ongoing studies. In several studies,22 the standard deviation of the change in gastric volume post-meal is 75 mL, and the mean change in volume is 450 mL. The sample sizes required to show a 25% difference in volume is nine per group for a parallel-group design (e.g. disease vs controls, drug vs placebo) and six for a cross-over design study. With a sample size of 45 per group (which would be needed with the barostat), SPECT imaging could detect an effect size of 10% (rather than 25% with barostat) in a parallel-group design. Similarly, for a cross-over study of 24 participants (which would be needed to show an effect size of 25% with the barostat), the effect size demonstrable with SPECT would be 10%. These data suggest that SPECT imaging is a more sensitive method to detect differences in gastric volume change due to disease or perturbation.

Disadvantages

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The main problem is the use of radioactive isotopes. The equipment is not widely available and sophisticated software is needed to perform the three-dimensional reconstruction. Measurements can only be obtained in the supine position, eliminating the influence of gravity, which is a drawback shared with MRI. Unlike the studies with the barostat balloon, gastric sensation cannot be assessed by SPECT alone; hence, the latter has to be combined with a water/nutrient drinking test to evaluate symptoms and sensation.

Potential applications

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With further validation of the method, SPECT will be a very useful tool in the clinical setting where SPECT cameras are available for diagnostic use.

Satiation drinking test

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In the methods discussed above, accommodation testing quantified the volume response to food ingestion, either by measuring proximal gastric volume (barostat, ultasonography) or by computing total gastric volume (MRI, SPECT). A recently published paper by Tack et al. proposes evaluating the rate at which satiety is reached in a subject as a surrogate for gastric accommodation.45 One has to question whether such a method that is critically dependent on sensation and psychological state relative to perception of a food load can truly be used to evaluate gastric volume in a multi-dimensional disorder like functional dyspepsia, which is associated with sensory, motor and psychological disturbances.

Principle

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A peristaltic pump fills two beakers at a rate of 15–30 mL min−1 with a liquid meal (Nutridrink®, Ensure®, Nutricia, Zoetermeer, The Netherlands). Subjects are requested to maintain oral intake at the filling rate. At 5-min intervals, they score their satiation level on a visual analogue scale that combines verbal descriptors on a scale graded 0–5 (1 = threshold, 5 = maximum satiety).

The amount of kcal ingested at maximum satiety is proposed as a surrogate for the magnitude of the gastric accommodation response. In a variation of the procedure, others ask subjects to drink 100 mL of water every minute.

Validating studies

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Boeckxstaens et al. published the first paper to investigate whether a drinking test (nutrient or water) would be a sensitive, non-invasive alternative for barostat studies.45 They found no difference in drinking capacity between dyspeptics with a normal accommodation response and those with impaired accommodation as assessed by the barostat. Furthermore, they found no significant relationship between drinking capacity and fundic accommodation, and they concluded that drink tests are not valid alternatives for barostat measurements and cannot predict pathophysiological mechanisms underlying functional dyspepsia.

In a recently published paper, Tack et al. reevaluated the method, using the procedure already described, and reached very different conclusions.45 They studied dyspeptics vs controls (P < 0.0001) and compared results of the nutrient drink test with previous data from barostat experiments (Fig. 6). It should be noted that barostat studies and drinking tests cannot be performed simultaneously.

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Figure 6. Relationship between the end point of the satiety drinking test and the size of meal-induced accommodation, determined by gastric barostat in healthy controls (n = 25) and in patients with functional dyspepsia (n = 37) (reproduced with permission from Ref. 45). Note the rather sigmoid presentation of the data (dashed line, drawn manually by us) as opposed to the linear regression presented in the original paper. This suggests that, for dyspeptic patients (the patient group to which such a test would be applied), there is no clear linear relationship between accommodation volume and kcal to maximum satiation. Thus, a narrow range of kcal intake to induce satiety (400–650 kcal) is associated with a very large range of meal-induced accommodation (0–330 mL). Similarly, for an accommodation in the narrow range of 180–280 mL, the associated kcal intake to satiation ranges from 400 to 1300 kcal. These data question the validity of using the satiety test as a surrogate for gastric meal accommodation.

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Correlation figures for controls and dyspeptics as a whole group, and for patients only were presented (r = 0.76, P < 0.001; and r = 0.71, P < 0.001; respectively). The correlation for healthy controls was not reported, but the data plotted clearly show that there is no correlation. Considering the distribution of data of dyspeptics (full dots), a dyspeptic who ingested, for example 500 mL before reaching satiety, could have a meal-induced accommodation between 0 and 300 mL. This range seems quite broad, especially if one considers that a volume response of 64 mL is the cut-off value for normal in the same laboratory. Thus, there is poor relation between volume tolerated and accommodation for these subjects. The data for dyspeptics seem to follow a sigmoid distribution rather than a linear relationship (Fig. 6).

Tack et al. also found a significant increase in amount of kcal ingested at maximum satiety with sumatriptan and this was associated with proximal gastric relaxation.45 Erythromycin had the opposite effect.

However, these pharmacological perturbations are quite sizeable, and it is still unclear whether this technique can actually function as a non-invasive method to quantify differences in gastric accommodation in disease relative to health, which may be relatively small. Comparison with other, more established and validated techniques (barostat, SPECT) is imperative, as is a thorough assessment of the reproducibility and reliability of this method. The impact of psychological bias and the influence of upper gastrointestinal symptoms on the surrogate marker for volume also need further study.

Advantages

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The satiety drinking test is simple, non-invasive and the cost is low, making it widely available.

Disadvantages

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Drawbacks are the subjective nature of the procedure and the possible influence of sensory and psychological factors. Reliability and validity have not been sufficiently demonstrated.

Potential applications

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The satiety drinking test is a very interesting technique for evaluating post-prandial sensation and symptoms, although its use for quantifying volume responses of the stomach remains questionable.

Principle

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The technique of water load testing in gastric accommodation studies was also first published by Boeckxstaens et al.46 Two techniques were described. The 5-min water load (5 WL) test requires the subject to drink tap water ad libitum over a 5-min period. An alternative approach demands ingestion of water at a rate of 100 mL min−1 until reaching the point of fullness. The volume of water consumed is measured in both approaches. The basic concept is thus identical to the satiety drinking test.

Validating studies

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Jones et al. studied this technique extensively, investigating the reproducibility of the 5 WL test on three occasions, separated by at least 2 weeks.47 Volumes to fullness between first and second tests were highly correlated (r = 0.77, P < 0.0001), but these measurements were not reproducible between the first and the third test. Controls seemed to ingest significantly more water than dyspeptic patients (P < 0.005). However, several dyspeptics had a tolerance of 0–100 mL, which suggests this was an unrepresentative tertiary referral patient group in whom visual perception bias and psychological disturbances influenced volume ingested. Hence, it is unlikely that the water load test could serve as a surrogate for gastric volume estimation.

Advantages

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Water load testing is simple, non-invasive, and the cost is low, making it widely available.

Disadvantages

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Reproducibility of the method is questionable. As with the satiety drinking test, the potential influence of symptoms and psychological factors appears significant.

Potential applications

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As Jones et al. suggest, insufficient evidence exists to support the routine use of the water load test in clinical practice. It may be a better measure of personal and psychological characteristics than an actual measure of gastric motor function!

Summary and a look to the future

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While gastric barostat studies have been the gold standard in this field to date, the invasive nature of the procedure and the potential for artefact introduced by the intragastric balloon create the need for a new approach. Ultrasound was the first technique, but its reliability and validity continue to be explored.

Methods to measure total gastric volume by means of three-dimensional reconstruction of the stomach followed. This is presently the most direct and accurate way to estimate the volumetric change with accommodation. MRI has an advantage over SPECT as it avoids the use of ionizing radiation. Nevertheless, consistent evidence for validity of the method in the literature is only available for SPECT imaging. The volume-based methods assess volume change, but cannot evaluate muscle tone change. These techniques are based on the assumption that volume change ‘tracks‘ tone change because pressure is maintained quite stable by gastric wall relaxation and emptying and by venting through the belch reflex.

Simpler techniques assume that the volume intake of water or a liquid meal reflects the volume of the stomach. Apart from questions concerning reliability and validity, it is unclear whether matching satiation (a parameter that is clearly subject to a multitude of environmental and personal psychological influences) to a volumetric parameter is valid. Drinking tests seem to have greater potential in the evaluation of gastric sensation and symptom generation after the ‘stress’ of food ingestion. Thus, MRI and SPECT seem to have the greatest potential for quantifying gastric accommodation, although further validation remains mandatory, especially for MRI (Table 1).

Table 1.  Comparison of measured end points, disadvantages and drawbacks for the different techniques
TechniquesEnd point(s) measuredAdvantagesDrawbacks
Intragastric barostat studiesProximal gastric volume at clamped pressure Compliance SensationValidated Current standardInvasive, uncomfortable Non-physiologic (balloon) Poor reliability
UltrasoundTwo-dimensional Proximal gastric area Proximal diameter Three-dimensionalNon-invasive, no radiation Low cost, available Also measures gastric emptyingUser-dependent Technical difficulties
Single photon emission computed tomographyTotal and regional gastric volume3-D estimation Well validated Non-invasiveRadiation Subjects in supine position Expensive, not widely available
Magnetic resonance imagingTotal and regional gastric volume3-D estimation Non-invasive, no radiation Describes gastric anatomy and motilitySubjects in supine position Expensive, not widely available No data on reliability
Nutrient/water drinking testsGastric ‘filling’ capacity and sensationSimple Available, low costNo evidence for reliability Sensation a suitable surrogate for volume?

In the future, we expect further validation of the imaging modalities, MRI and SPECT application in pharmacodynamic studies and ultimately in clinical practice. The measurement of gastric accommodation and sensation with validated, reliable and non-invasive tests has the potential to impact the management of idiopathic and secondary dyspepsia in adults and adolescents.

Acknowledgments

  1. Top of page
  2. Abstract
  3. References

This study was supported by grants RO1-DK54681 and K24-DK02638 to Dr Camilleri from National Institutes of Health.

References

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