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Gastric Motility Breath Test Background |
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It has
been estimated that symptoms of functional gastrointestinal
disorders, those without noticeable structural, infectious,
or biochemical cause, occur to some degree in nearly
one quarter of all individuals who are otherwise healthy
(1,2). Of those who seek treatment, many are diagnosed
with non-ulcer dyspepsia (NUD), endoscopy-negative gastroesophageal
reflux disease (GERD), and irritable bowel syndrome.
These functional disorders are often caused or exacerbated
by gastrointestinal motility disturbances or gastroparesis
(delayed gastric emptying). The non-specific nature
of symptoms often requires gastric emptying to be measured
objectively.
Gastric scintigraphy is currently the established procedure
for monitoring solid and liquid phase gastric emptying.
This technique monitors gastric emptying directly by
measuring the transit time of a radiolabeled test meal.
The test meal is labeled with a gamma emitting marker
prior to ingestion. A gamma camera positioned over the
abdomen monitors the change in signal as the test meal
is digested.
Breath tests employing stable isotopes offer an alternative
to scintigraphic techniques for the measurement of gastric
emptying. The 13C-octanoate breath test (OBT)
has been shown to measure solid phase gastric emptying
and correlates with scintigraphic emptying of an egg meal
(3). In this test, 13C-octanoate is mixed
into an egg and baked into a meal at the clinical site. Metabolic
Solutions has been active in developing a commercially
viable alternative to the 13C-octanoic acid
breath test. Widespread use of the OBT has not occurred
because it is not clinically
practical due to the inconvenience and lack of
uniformity of cooking the egg-based test meal and the
demanding time requirement for breath collection. Our
research efforts have resulted in a product we call the
Gastric Motility Breath Test (GMBT). The GMBT uses an
easy to prepare, low-fat muffin
meal along with Metabolic Solutions simple breath
collection system to provide a convenient and reliable
means to monitor solid phase gastric emptying. This
test is a significant advancement in promoting rapid and
successful diagnosis for individuals suffering from motility
disorders.
Principle of the Gastric Motility Breath Test
A muffin test meal is labeled with 13C-octanoate
and administered after an overnight fast. Octanoic acid
is a naturally occurring eight-carbon, medium chain fatty
acid (MCFA) typically found in butter as an ester.
MCFAs are absorbed by the small intestine and rapidly
transported to the liver bound to serum albumin. In the
liver, MCFAs freely enter the mitochondria where they
are oxidized to CO2. This process is depicted
below:
Gastric emptying is estimated by monitoring the appearance
of 13CO2 in breath subsequent to
ingestion and metabolism of 13C-octanoate.
Mathematical analysis of the 13CO2
appearance in breath reveals estimates of gastric emptying
parameters. The octanoic acid breath test is an
indirect measure of gastric emptying because the 13CO2
appearance curve reflects the sum influence of gastric
emptying, digestion, absorption, and metabolism. However,
the metabolic processing of octanoate is rapid and reproducible,
thus delays in emptying are due to differences in gastric
motility.
Limitations of Current Gastric Emptying Tests
There are significant limitations with scintigraphy that
prevent its frequent use. A scintigraphic examination
costs approximately $1000; requires access to expensive
equipment and highly trained personnel; and exposes patients
to ionizing radiation. In addition, due to the nature
of the test procedure, the instrument is only capable
of performing a few scintigraphies per day. As a
result, scintigraphy is impractical for monitoring the
course of treatment and is not an attractive diagnostic
option.
The GMBT has several advantages over scintigraphy:
- no radioactivity;
- the test can be administered at any location;
- only limited medical training is required
to administer the test;
- lower cost;
- it can be repeated as necessary to monitor
treatment, and
- the results are operator independent and
will not vary among locations.
Although the principle of the GMBT
is biochemically similar to the Octanoate Breath Test
described by Ghoos (3), it improves upon the original
concept because it replaces the egg meal with a standardized,
easy to prepare muffin meal. For the egg-based
tests, the yolk and egg white are first separated because
the tracer is only readily solubilized in the yolk.
The octanoic tracer is added to the yolk, which is then
beaten. The egg white is added back and again
beaten, followed by cooking by stove top/burner. In
comparison, the GMBT uses a standardized muffin meal
requiring just the addition of water to a powdered mix,
stirring of the contents, and microwaving for 1-2 minutes.
The GMBT has several advantages over the Octanoate Breath
Test with egg-based meal:
- standardization of the meal (eggs vary in
caloric content, size and composition)
- ease of preparation
- is operator independent
- standardized cooking conditions allows valid
inter-clinical site
comparisons
References
(1) Parkman, H.P., M.A. Miller and
R.S. Fisher. Sem. Nucl. Med. 1995; 25:289-305.
(2) Horowitz, M. and R.J.L. Fraiser. Scand. J. Gastroenterol.
1995; 30:7-16.
(3) Ghoos, Y.F., B.D. Maes, B. Geypens, G. Mys, M.I.
Hiele, P.J. Rutgeerts and G. Vantrappen. Gastroenterology
1993; 104:1640-1647. |
Metabolic Solutions, Inc., 460
Amherst Street, Nashua, NH 03063
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