Recent Advances in Gastric Function Testing
acid) or a proteinaceous alga (Spirulina) to label the solid component of a test meal.20,21
The substrate labeled with 13C is absorbed in the duodenum,
metabolized in the liver, and exhaled from the lungs as 13CO2, which can be measured by isotope ratio mass spectrometry or laser infrared spectroscopy. This test assumes that gastric emptying is the
rate-limiting step in the absorption and metabolism of the 13C-labeled substrate (see Figure 1). In healthy volunteers, measuring
breath 13CO2 every 15 minutes over three hours there was excellent correlation (r = 0.88) in gastric emptying comparing scintigraphy (GES) and Spirulina breath testing. Sensitivity for breath testing was measured at 86% and specificity of 80% to detect delayed gastric emptying22 (see Figure 2).
Stable isotope breath testing shows promise as a convenient alternative to GES for measuring gastric emptying. This is especially true for facilities that do not have access to gamma cameras or in situations where radiation should be avoided, such as in pregnancy or in children. Samples can be collected in the clinic or by the bedside, preserved, and then sent to a laboratory for analysis. However, breath testing may not be accurate in patients with diseases of the liver or pancreas, where substrate metabolism may be the rate-limiting step rather than gastric
emptying. Similarly, patients with chronic lung disease may alter 13CO2 excretion. Stable isotope breath tests can only measure global gastric emptying whereas GES can assess both global as well as regional differences in emptying. Currently, breath testing is not US Food and Drug Administration (FDA) approved for measurement of gastric emptying and there is a lack of a commercially available standard meal, which prevents more widespread clinical use. Finally, further studies are required to determine the accuracy and reproducibility of breath testing in patients with markedly abnormal gastric emptying. However, stable isotope breath testing may become a convenient alternative to assess meal-related gastric emptying for clinicians.
SmartPill
The SmartPill (SP) GI Monitoring System is an FDA-approved device that measures gastric emptying time (GET) and can simultaneously assess motility parameters in the stomach, small bowel, and colon. SP is a non-invasive, non-digestible wireless capsule that travels through the GI tract and measures luminal pH, pressure, and temperature, which is then transmitted to a receiver that captures the data. Gastric emptying is signaled by an abrupt rise in pH (>3 pH units) from gastric baseline as the capsule passes from the acidic gastric antrum to the more alkaline duodenum. SmartPill empties with the phase III MMC, which indicates completion of the post-prandial phase and return to the fasting condition, or with high amplitude antral contractions.23
It is important to
note that a solid meal may empty before indigestible solids, such as SP (see Figure 3). A GET <5 hours is considered normal and can help to differentiate between healthy and gastroparetic subjects. SP has been shown to highly correlate with GES (r = 0.73) and demonstrated sensitivity of 87% with specificity of 92%. SP can also provide specific (gastric, small bowel, and colonic) transit times as well as whole gut transit times24
(see Figure 4).
In addition, SP can measure motility parameters in the stomach, small bowel, and colon in healthy and symptomatic subjects.25,26
Parameters including number of contractions (Ct) and motility index (MI) US GASTROENTEROLOGY & HEPATOLOGY REVIEW
Figure 3: Relationship Between Gastric Emptying Scintigraphy and Gastric Emptying Time of the Wireless Motility Capsule
A 100
10 20 30 40 50 60 70 80 90
0 0.0 0.5 1.0 1.5 2.0 B 100
10 20 30 40 50 60 70 80 90
0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Elapsed time (h)
Correlations of gastric emptying time (GET) to A gastric emptying scintigraphy (GES)–two hours at r = 0.63; (b) GES–four hours at r = 0.73, with respective regression lines and 95% confidence interval bars. For both scintigraphic and GET measurements, n = 125. Times >360 minutes were capped at 360 because of the introduction of another meal. Vertical dashed lines in B represent the cut-offs used to determine abnormal gastric emptying by scintigraphy. Note meal emptying measured by GES may occur after GET. Reproduced with permission from Kuo B, et al., 2008.47
defined as Ln (sum of pressure amplitudes * number of contractions + 1) can be analyzed 60 minutes before and 40 minutes after GET to determine gastric and small bowel motility, respectively. Sixty healthy subjects with GET <5 hours were compared with 33 gastroparetic patients with GET >5 hours using SP, which showed gastroparetics had statistically lower gastric and SB motility parameters. The gastric Ct cut- off was 29 and the SB Ct cutoff was 36 with a specificity of 95%.26
Thus,
SP has the ability to discriminate between normal and impaired motility in the stomach and small bowel.
SP is already FDA approved for measurement of gastric pH, GET, and whole gut transit times and offers an alternative to GES. The single largest advantage of SP over other modalities is that it can measure emptying and contractile parameters in the stomach, small bowel, and colon to allow for investigation of regional as well as global dysfunction of the GI
19 4.0 4.5 5.0 5.5 2.5 3.0 3.5 Elapsed time (h)
0 1 2 3 4 5 6 7
6.0 4.0 4.5 5.0 5.5
0 1 2 3 4 5 6 7
6.0
% of meal remaining
% of meal remaining
pH
pH
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