Upper Gastrointestinal Tract
Figure 1: Comparison of Gastric Emptying t½ Time by Scintigraphy and 13C octanoic Acid Breath Test using a Generalized Linear Model
Three sample data
160 140 120 100 80 60 40
1 2
y=x line r=0.86 SD∆ 40 60 80 100
=10 minutes (-23 to 17)
120 140 160 t by breath test (minutes)
160 140 120 100 80 60 40
1 2
y=x line
colloid-labeled egg sandwich serves as the test meal in most centers and emptying is measured at zero, one, two, and four hours.13
Abnormal
Regional emptying can also be assessed to evaluate fundal and antral function, which can help explain symptoms, especially in the setting of normal global function.14
issue, as the coefficient of variation is almost 15%.15
gastric emptying is defined as >10% of the meal remaining at four hours.11
However, reproducibility remains an Also, some centers
measure emptying for a period of 90 minutes and use a computer-generated curve to predict gastric emptying rates, such as half-emptying time (t1/2). However, if emptying has not reached 50%, the extrapolated value for t1/2 may not be reliable.16
r=0.80 SD∆ 40 60 80 100
=10 minutes (-27 to 29)
120 140 160 t by breath test (minutes)
Three-sample data at baseline, 90, and 180 minutes (right) showed a good correlation of gastric emptying t1/2 time between the scintigraphy and the breath test, as did three-hour data (left). The slope of the regression line for t1/2 approximated the line of identity (y = x line), and standard deviation of differences was 10 minutes. Reproduced with permission from Lee JS, et al., 2000.46
Figure 2: Schematic Design Depicting Stable Isotope Breath Test to Measure Gastric Emptying
Finally, exposure to
radiation may not be desirable in certain patient populations. Gastroduodenal manometry evaluates gastric and duodenal contractile activity as well as amplitude and patterns of contractions. This is performed in stationary settings for five- to eight-hour periods or in an ambulatory fashion over 24 hours. Recordings performed over 24 hours may be able to provide a more complete understanding of pathophysiology as this can capture migrating motor complexes and also correlate abnormal contractile patterns with symptoms.6
Certain 13CO2 exhaled from lungs 13
C-labelled substrate
manometric findings may correlate with specific disease states. For example, in gastroparesis, gastroduodenal manometry may show a decrease in the frequency or amplitude of antral contractions while phase III contractions may begin in the duodenum rather than the antrum. Gastroduodenal manometry can also help to differentiate between neuropathic versus myopathic diseases. Myopathic disorders, such as amyloid or scleroderma, are characterized by abnormally low amplitude contractions. Neuropathic disorders, on the other hand, produce normal amplitude contractions but have abnormal propagation, including loss of intestinal phase III contractions, random bursts, and loss of conversion to the fed pattern after meal ingestion.17
is rarely used, as this test is invasive, uncomfortable for the patient, and not readily available to most clinicians.
C-substrate metabolized in liver and pancreas
13
Gastric emptying is rate limiting step
Stable non-radioactive isotope 13C is bound to substrate (octanoic acid or Spirulina), absorbed rapidly in the duodenum, metabolized in the liver, and exhaled as 13CO2 from the lungs, which can be measured by isotope mass spectroscopy. Gastric emptying is normally the rate-limiting step. However, rates of gastric emptying may not be accurate in diseases of the liver or pancreas, where substrate metabolism may be the rate-limiting step. Similarly, chronic lung diseases may also cause abnormal rates of gastric emptying.
investigating gastric motor and sensory functions, objective evidence is gathered to help with the understanding of non-specific symptomatology.
Current Standard Tests
Standard tests employed to understand the physiology and pathophysiology of gastric motility include scintigraphic emptying, gastroduodenal manometry, electrogastrography (EGG), and barostat studies. Gastric emptying scintigraphy (GES) is the gold standard currently for evaluation of gastric emptying. A 99mTc sulfur
18
Electrogastrography (EGG) measures gastric myoelectric activity or slow waves by affixing cutaneous electrodes to the anterior abdomen. An EGG is defined as abnormal when myoelectric activity occurs more than 30% of the time and/or when ingestion of a meal does not have a corresponding increase in signal amplitude. This correlates to some degree with delayed gastric emptying of solids. However, correction of these dysrhythmias seen by EGG has not been shown to improve symptoms and remains mostly a research tool.18
gold standard for measuring gastric accommodation and involves introduction of a balloon into the fundus to measure intraballoon volume or pressure. It also can quantify gastric sensation by correlating symptoms with volume or pressure. However, gastric barostat is invasive, uncomfortable for patients, time-consuming, and requires skilled operators. Furthermore, it is only performed in certain centers and remains primarily a research technique.19
However, gastrouodenal manometry
Gastric barostat is the
Because of issues with
invasiveness, poor tolerability, exposure to radiation, and inaccessibility of testing centers, several novel techniques are being developed to investigate gastric function that can improve upon these modalities.
Stable Isotope Breath Tests
Stable isotope breath tests were developed as a convenient method to measure gastric emptying. The stable non-radioactive isotope, 13C, can be bound to a substrate, either a medium-chain triglyceride (octanoic
US GASTROENTEROLOGY & HEPATOLOGY REVIEW
t by scintigraphy (minutes)
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t by scintigraphy (minutes)
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