Am J Physiol Gastrointest Liver Physiol 296: G709–G716, 2009.
First published December 18, 2008; doi:10.1152/ajpgi.90318.2008.
Every slow-wave impulse is associated with motor activity
of the human stomach
Michael Hocke,1 Ulrike Schöne,1 Hendryk Richert,2 Peter Görnert,2 Jutta Keller,3 Peter Layer,3
and Andreas Stallmach1
1
Clinic of Internal Medicine II, Department of Gastroenterology, Hepatology and Infectious Diseases, Friedrich Schiller
University Jena, 2Innovent Jena, Germany; and 3Israelitic Hospital, Academic Hospital University of Hamburg,
Hamburg, Germany
Submitted 2 May 2008; accepted in final form 8 December 2008
electrogastrography; pacemaker; magnetic marker; magnetic monitoring; 3D-MAGMA
the stomach include secretion,
digestion, storage, mixing, and emptying of nutrients. To
achieve this, control mechanisms are required to coordinate
gastric secretion and motility. Efferent signals from the central,
spinal, and enteric nervous system determine gastric contractility. Modified muscle cells, the interstitial cells of Cajal, also
play an important role for gastric motility: They are believed to
produce the slow waves (24, 29), which are spontaneous
depolarizations and repolarizations of the membrane potential
of these cells that occur with a frequency of 3 cpm (counts per
minute). It is believed that the depolarizations associated with
slow waves by themselves are subthreshold and do not suffice
PHYSIOLOGICAL FUNCTIONS OF
Address for reprint requests and other correspondence: M. Hocke, Clinic of
Internal Medicine II, Dept. of Gastroenterology, Hepatology and Infectious
Diseases, Friedrich-Schiller-Univ. Jena, Erlanger Allee 101, D-07747 Jena,
Germany (e-mail: [email protected]).
http://www.ajpgi.org
to induce muscle contractions (8, 13, 54). Instead, additional
neural signals are needed to increase the membrane potential
above this threshold and to induce spike-wave activity, which
is associated with muscle contraction. Spike-wave activity
occurs irregularly but depends on the frequency of the slow
waves. However, because of their irregular appearance, it is
impossible to record spike waves by using detectors with
surface electrodes (10, 50). Thus it is generally accepted that
the recording taken by electrogastrogram (EGG) reflects slowwave activity but not occurrence of stomach contractions (8,
13, 54).
In 2003 a high-resolution three-dimensional magnetic detector system called 3D-MAGMA was developed by Richert (39).
This new system allows precise localization of a small magnetic marker and determination of its three-dimensional orientation inside a human body. When we used this system in a
preliminary study we recorded periodical movements of the
magnetic marker at a frequency of 3 movements per minute
(mpm) as long as the marker was in the stomach. These
movements were by far too small to be detected by conventional methods for evaluation of gastric motility such as manometry (12), X-ray imaging (49), or MRI (27). Since the
frequency of the marker movements was identical with the
frequency of gastric slow waves, it is intriguing to hypothesize
that each gastric slow wave does induce a motor response that
is not strong enough to be detected by conventional methods.
To test this hypothesis, we compared occurrence of gastric
slow waves and of slight movements of a magnetic marker
inside the stomach of healthy volunteers using the 3D-MAGMA
system.
PATIENTS AND METHOD
Twenty-one healthy volunteers (11 men and 10 women) participated in the study. Mean age of the women was 35.8 ⫾ 11.6 yr, and
of the men it was 40.4 ⫾ 13.6 yr. In all volunteers informed, written
consent was obtained, and all studies were performed according to the
Declaration of Helsinki. The study was evaluated and approved by the
ethical board of the Friedrich Schiller University Jena.
For recording of slow-wave activity, electrogastrographies (EGG;
Medtronic, Minneapolis, MN) were performed (47). Our system
consists of four channels for the electric signals plus one channel to
filter out artifacts such as muscle movements. The signal channels
were positioned at the abdominal surface in projection above the
larger curvature of the stomach, channel 1 over the fundic region to
channel 4 over the antral region, as shown in Fig. 1.
The costs of publication of this article were defrayed in part by the payment
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0193-1857/09 $8.00 Copyright © 2009 the American Physiological Society
G709
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Hocke M, Schöne U, Richert H, Görnert P, Keller J, Layer P,
Stallmach A. Every slow-wave impulse is associated with motor
activity of the human stomach. Am J Physiol Gastrointest Liver
Physiol 296: G709 –G716, 2009. First published December 18, 2008;
doi:10.1152/ajpgi.90318.2008.—Using a newly developed high-resolution three-dimensional magnetic detector system (3D-MAGMA),
we observed periodical movements of a small magnetic marker in the
human stomach at the typical gastric slow-wave frequency, that is 3
min⫺1. Thus we hypothesized that each gastric slow wave induces a
motor response that is not strong enough to be detected by conventional methods. Electrogastrographies (EGG, Medtronic, Minneapolis, MN) for measurement of gastric slow waves and 3D-MAGMA
(Innovent, Jena, Germany) measurements were simultaneously performed in 21 healthy volunteers (10 men, 40.4 ⫾ 13.6 yr; 11 women,
35.8 ⫾ 11.6 yr). The 3D-MAGMA system contains 27 highly sensitive magnetic field sensors that are able to locate a magnetic pill inside
a human body with an accuracy of ⫾5 mm or less in position and ⫾2°
in orientation at a frequency of 50 Hz. Gastric transit time of the
magnetic marker ranged from 19 to 154 min. The mean dominant
EGG frequency while the marker was in the stomach was 2.87 ⫾ 0.15
cpm. The mean dominant 3D-MAGMA frequency during this interval
was nearly identical; that is, 2.85 ⫾ 0.15 movements per minute. We
observed a strong linear correlation between individual dominant
EGG and 3D-MAGMA frequency (R ⫽ 0.66, P ⫽ 0.0011). Our
findings suggest that each gastric slow wave induces a minute contraction that is too small to be detected by conventional motility
investigations but can be recorded by the 3D-MAGMA system. The
present slow-wave theory that assumes that the slow wave is a pure
electrical signal should be reconsidered.
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Because EGG recording was always best in channel 3 (located
above the upper antrum), data from this channel were used for further
evaluation. To avoid motion artifacts, which necessitate cleaning of
the EGG signal, volunteers were asked to lie without any movement
on a diagnostic bed during the whole recording. The data were
measured at a frequency of ⬃104 Hz, filtered, averaged, and recorded
with a frequency of 1 Hz. No changes to the commercial EGG system
were made for data collection.
The magnetic monitoring system 3D-MAGMA (Innovent, Jena,
Germany) (40, 41) was used for the investigations. It contains 27
highly sensitive magnetic field sensors (anisotropic magneto resistive)
that are arranged contact free above the abdomen of the volunteer (see
Fig. 2). The system measures the magnetic field of a small permanent
magnetic capsule and calculates, by using all sensor signals, its
three-dimensional position and orientation. The method uses nonlinear optimization algorithms similar to the well-described Magnetic
Tracking System (43) and Magnetic Marker Monitoring (51–53).
The capsule, shown in Fig. 3, comprises a magnetic core and a
bioinert polymer shell (outer diameter 6 mm, overall length 18 mm,
density ⬃2 g/cm3). Such a capsule moves, driven by the natural
peristalsis, through the complete gastrointestinal tract. Because of the
weight of the capsule, the capsule is positioned close to the inner
stomach wall after ingestion. We confirmed this endoscopically in two
different volunteers in the preexperimental phase. Accordingly, we
are sure that the signals from the marker reflect the movement of the
stomach wall.
Fig. 2. Sensor system above the abdomen of a volunteer. Each of the three
modules contains 9 magnetic field sensors in 3 groups (position marked by the
triangles). Data from all sensors allow calculating 3D position and orientation
of the magnetic marker.
Fig. 3. Magnetic marker with polymer shell, length: 18 mm, diameter: 6 mm,
density: 2 g/cm3.
The 3D-MAGMA system allows the tracking of a single capsule in
three-dimensional space with high accuracy in position and orientation at a measurement frequency of up to 50 Hz. It can be used in a
normal clinical environment without any special precautions.
The accuracy of the marker detection relies on the available
magnetic field strength at the sensors positions induced by the capsule.
This available magnetic field is strongly dependent on the distance
between capsule and magnetic field sensors and is given in the range
of 10⫺8 to 10⫺5 T. In Fig. 4 the accuracy of the measured position
within a plane 150 mm below the sensors is shown. Within the whole
gastrointestinal tract the maximum position error is less than ⫾5 mm
(resolution: ⬍1 mm) and the orientation error is less than ⫾2°
(resolution: ⬍0.5°).
The magnetic field induced by the capsule does not interfere with
human tissue or any other devices within the measurement volume as
long as these devices do not contain any magnetizable components.
Fig. 4. Measured lateral accuracy of the 3-dimensional magnetic detector
(3D-MAGMA) system. Within the dark area the deviation of the true marker
position is within ⫾5 mm whereas in the lighter areas the deviation of the
marker position can increase up to 15 mm. The measurement demonstrates that
in a range from at least 30 ⫻ 30 cm2 the accuracy for detecting the magnetic
marker is excellent. The sensors were positioned 150 mm above the measured
area. Each sensor triplet is represented by a triangle. Measurements were done in
comparison to an optical 3D measurement system (Easytrack 500, Atracsys).
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Fig. 1. Position of the signal channels in a human model.
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Fig. 5. Path of a capsule through a volunteer’s intestinal tract.
The overall duration of this measurement was 2 h 20 min. The
measurement started with the capsule inside the esophagus, the
transit through the stomach took 1 h 10 min. Beginning from
the duodenum the capsule moved ⬃2.4 m with an average
velocity of 3.4 cm/min. The position of the magnetic sensor
triplets in their modules are shown as triangles.
Table 1. Parameters for evaluation provided by the
3D-MAGMA system
3D position and orientation
of the marker
Path
Path length
Local travel velocity
Travel and stopping times
Frequency patterns
Power of movement
3D-MAGMA measures and stores twice per
second the three-dimensional position and
the orientation of the magnetic marker (x,
y, z, ␸, ␽).
3D-MAGMA shows the 3D path of the
marker through the volunteer’s intestinal
tract (position of stomach, duoenum, and
large intestine are anatomically fixed).
Knowing the 3D path, the system calculates
partial or overall path lengths.
Using the positions and the time, the
software calculates local and overall
velocity.
Digestive motility shows active and passive
phases. Therefore the software calculates
travel times and travel pauses.
3D-MAGMA calculates for every position,
for arbitrary periods, and for the whole
measurement the FFT patterns. For this
study we used the FFT of the orientation
changes.
Real part of the Fourier analysis shows the
intensity of movement.
3D-MAGMA, 3-dimensional magnetic detector system; FFT, fast Fourier
frequency.
recorded EGG data. Thus comparison of electrical activity of the
stomach and mechanical movement of the capsule is easy to perform.
Because of the high sensitivity of the 3D-MAGMA system it is
possible to reveal even very weak movements by evaluating alterations of capsule orientation. Figure 6 shows typical orientation
changing of a capsule inside the stomach of a healthy volunteer. The
changes of the orientation mostly were larger than 10° and could
easily be evaluated. Because of the fact that the change of orientation
of the marker is much more reliable than the movement in a threedimensional space, we used these data for our analysis. It should be
mentioned that we were able to find the same frequencies in the
markers position in three-dimensional space; however, because of
small changes of the marker position, these frequencies were too
inconstant to use for the comparison with the EGG signal.
Measurements always took place in the morning between 8 and 12
AM and all subjects had been fasting for at least 8 h.
At first, the EGG electrodes were placed on the abdominal surface
as described above after cleaning the area with Softasept N (Braun
Melsungen) alcoholic solution. Then the recordings were started only
if a clear, artifact-free signal was obtained. After that the volunteer
was placed on the diagnostic bed under the magnetic field sensor
system and was asked to swallow the magnetic pill with 70 ml of
water and to avoid movements. Figure 7 shows a volunteer during the
measurement procedure. The measurement ended with the passage of
the magnetic pill through the pylorus, which was observed online and
Fig. 6. Typical measurement of orientation deviation of the 3D-MAGMA
capsule inside the stomach. The orientation of the capsules changes typically
in the range of more than 10° because of the stomach wall movement. The
frequency of ⬃3 min⫺1 can be seen quite clearly. Sometimes these changes
can be found in the range of up to 60°!
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The simultaneously used EGG electrodes are made out of nonmagnetic metal and plastics.
Figure 5 shows a typical recorded path of a capsule inside a
volunteer’s gastrointestinal tract.
Muscle movements of the stomach or the small intestine as well as
electrophysiological phenomena of the intestine are able to induce a
magnetic field by themselves. However, this field has a strength of
only ⬃10⫺12 T (5) and cannot be recorded by the 3D-MAGMA
system. Thus the calculated movements of the magnetic pill can be
seen as real movements and do not interfere with any other effects. To
illustrate this, we performed additional experiments with the capsule
outside the body of a healthy volunteer as described below.
The 3D-MAGMA system provides several parameters for evaluation (Table 1).
For this study we measured at a frequency of 50 Hz and used the
filtered and averaged data for evaluation at a frequency of 2 Hz.
With the 3D-MAGMA software it is possible to mark stomach and
duodenum and to calculate most important local parameters automatically as most frequently appearing frequency, covered path, capsule
velocity, and power. It is also possible to evaluate simultaneously
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Table 2. EGG and 3D-MAGMA data in healthy volunteers
3D-MAGMA (mpm)
EGG (cpm)
2.85
0.15
2.5
3
2.9
2.87
0.15
2.7
3.3
2.9
Mean
SD
Minimum
Maximum
Median
A typical example of both recordings (3D-MAGMA and electrogastrography (EGG)) is shown in Fig. 8 using the fast Fourier transformation into a
pseudo-3D running spectrum graph. The graphs display the frequency (x-axis)
and amplitude (y-axis) of signals recorded over time (z-axis). It can be clearly
shown that the dominant frequency detected by the 3D-MAGMA system (2.8
mpm, Fig. 8A) is identical with the dominant EGG frequency (Fig. 8B).
was clearly visible in every person by using the real-time position
graphic of the marker on the computer screen of the 3D-MAGMA
system.
As explained above, the 3D-MAGMA recordings reflect movements of the marker when placed intragastrically. To prove that there
are no interferences of the magnetic signal with environmental or
physiological electrical signals, we performed parallel measurements
of the EGG signal and the 3D-MAGMA signal with the magnetic
marker outside of a healthy volunteer (the marker was placed at the
abdomen without and with direct contact to the abdominal wall) and
after ingestion of the magnetic marker in four different people.
Combined EGG and 3D-MAGMA measurements as described
above were repeated in four healthy volunteers four times on different
days to evaluate intra- and interindividual variability of the measurements.
All data obtained from EGG measurements and the magnetic
markers orientation information from the 3D-MAGMA system during
Fig. 8. Fast Fourier transformation over a period
of 15 min using the raw data of electrogastrography (EGG; A) and 3D-MAGMA (B), both with
normalized amplitudes. C.P.M., counts per minute.
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Fig. 7. Measurement system for investigation of the magnetic marker transit
through the human digestive system.
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residence of the marker in the stomach was used for analysis by fast
Fourier transformation (FFT). To achieve comparable results, we used
the inbuilt 3D-MAGMA FFT function for analyzing both EGG and
3D-MAGMA data. To visualize frequency abnormalities more easily,
a so-called pseudo-three-dimensional running spectrum graph was
derived from the FFT calculation in every person as shown in Fig. 8.
This kind of displaying the results is routinely used for analyzing
EGG signals because it is easy to detect frequency abnormalities such
as bradygastria or tachygastria.
The statistical analysis was performed using the program GraphPad
Instat3. Relevant data obtained in all volunteers over a period of at
least 19 min are given as mean, standard deviation, median, minimum,
and maximum. The intraindividual and interindividual variation coefficient was also calculated. The Pearson correlation analysis was
used to evaluate linear correlations between 3D-MAGMA data in
movements per minute and EGG data in counts per minute. A P
value ⬍ 0.01 was considered significant.
RESULTS
The mean gastric transit time of the marker was 62.4 ⫾ 40.5 min.
The shortest transit time was 19.13 min, the longest 154.1 min.
In our group of healthy volunteers the mean frequency of the
movement of the magnetic marker was 2.85 ⫾ 0.15 mpm while
the marker was placed in the stomach. The mean frequency of
the slow-wave activity recorded by using the EGG was 2.87 ⫾
0.15 cpm (Table 2). EGG and 3D-MAGMA data did not differ
between male and female subjects and did not depend on the
age of the volunteers.
Fig. 10. Fast Fourier transformation of EGG
and 3D-MAGMA frequency with the marker
on top of a volunteer with direct contact to the
abdominal wall. Dotted line, EGG signal with
dominant frequency of 2.8 cpm; dashed line,
3D-MAGMA frequency with a dominant frequency in the range of 11–14 movements per
minute (mpm) (respiration).
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Fig. 9. Correlation of 3D-MAGMA and EGG data (R ⫽ 0.66, P ⫽ 0.0011).
A typical example of both recordings (3D-MAGMA and
EGG) is shown in Fig. 8 using the FFT into a pseudo-threedimensional running spectrum graph. The graphs display the
frequency (x-axis) and amplitude (y-axis) of signals recorded
over time (z-axis). It can be clearly shown that the dominant
frequency detected by the 3D-MAGMA system (2.8 mpm, Fig.
8A) is identical with the dominant EGG frequency (Fig. 8B).
Overall, there was a strong linear correlation between the
dominant frequencies of the 3D-MAGMA signals and the
dominant frequencies of the EGG in all 21 volunteers as shown
in Fig. 9 (r ⫽ 0.66, P ⫽ 0.0011). EGG data of one healthy
volunteer showed a particularly high frequency of gastric slow
waves (3.3 min⫺1), which clearly exceeded the 95th percentile
calculated for our group of healthy volunteers. When this
outlier was excluded, the linear correlation between EGG and
3D-MAGMA data became even more obvious (R ⫽ 0.8265,
P ⱕ 0.0001).
Exclusion of interference of 3D-MAGMA recordings with
physiological electrical signals. When the magnetic marker
was placed on the abdominal wall of a volunteer, only the
respiration frequency could be detected with the 3D-MAGMA
system (11–14 mpm), whereas the simultaneously performed
EGG showed the expected dominant frequency of ⬃3 cpm plus
the respiration artifacts (2.8 cpm and 11–14 cpm, Fig. 10).
Measurements obtained in the same subject after ingestion
of the magnetic marker into the stomach immediately showed
parallel dominant frequencies of 2.6 cpm in the EGG signal
and 2.6 mpm in the 3D-MAGMA signal (Fig. 11). Similar
results were also obtained in the other three volunteers in
whom these experiments were performed.
Moreover, compared with the EGG signal, the motion signal
from the magnetic marker was much clearer without showing
other disturbing frequencies. This is due to the fact that the
gastric slow-wave activity detectable at the abdominal skin
interferes with multiple electrical phenomena such as heart
action and muscle activity of the breathing muscles whereas
the movement of the magnetic marker in the stomach is
obviously not interfered by environmental or physiological
magnetic signals.
Intra- and interindividual variability of 3D-MAGMA measurements. To test intra- and interindividual variability of the
measurements, parallel 3D-MAGMA and EGG studies were
repeated in four healthy volunteers four times on different
days. For the 3D-MAGMA data the intraindividual variation
coefficient was 3.55% and the interindividual variation coefficient was 6.35%, reflecting a very good, high reproducibility.
Data are given in Table 3.
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Fig. 11. Parallel dominant frequency of EGG
signal (dotted line) and 3D-MAGMA signal
(dashed line) after ingestion into the stomach in
1 healthy volunteer. The second peak of the
dotted line corresponds to the breathing frequency that can be seen regularly in the EGG
signal.
DISCUSSION
Table 3. Interindividual and intraindividual variation coefficients of 3D-MAGMA data obtained in 4 healthy volunteers in 4
measurements on different days
Subject
1
2
3
4
Interindividual
Mean
SD
Variation coefficient (%)
1st
2nd
3rd
4th
Mean
SD
Variation Coefficient (%) Variation Coefficient (%)
Measurement Measurement Measurement Measurement Intraindividual Intraindividual
Intraindividual
Interindividual
3.0
2.8
3.0
2.5
3.0
2.9
3.1
2.7
3.0
2.9
2.9
2.6
3.0
2.8
2.7
2.7
3.0
2.9
2.9
2.6
0
0.1
0.2
0.1
2.8
0.2
8.4
2.9
0.2
5.8
2.9
0.2
6.1
2.8
0.1
5.1
2.9
0.1
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0
3.5
6.9
3.9
6.35
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The findings of our present study suggest that small movements of an intragastric magnetic marker occur in close correlation with and at the same frequency as gastric slow-wave
activity in healthy humans. From these findings we conclude
that, in contrast to previous assumptions, every gastric slow
wave is indeed followed by a tonic muscle contraction that may
be too small and/or too slow to be recorded by conventional
measuring techniques.
For our study we used the 3D-MAGMA system, which has
been developed and successfully applied as a reliable, cheap,
and side effect-free method to describe the transit of a marker
through the human gastrointestinal tract in vivo. The latest
release of this system allows measurements over a long period
of time and has a high resolution (detects marker movements
⬎5 mm in a three-dimensional space and alterations of marker
orientation ⬎2°). Thus this system is able to record movements
within the gastrointestinal tract in vivo that cannot be detected
with the help of currently available diagnostic methods because
they are too small and/or too slow.
Since the strength of the magnetic field induced by the
intragastric marker and recorded by the 3D-MAGMA system
exceeds the strength of magnetic fields caused by physiological
events such as muscle activity by several orders of magnitude,
it is physically impossible that the 3D-MAGMA signal interferes with such events. To illustrate the absence of interference
we compared 3D-MAGMA and EGG signals in four healthy
subjects while the marker was outside the body and after
ingestion of the marker. As expected, only respiration-driven
3D-MAGMA frequency could be detected when the magnetic
marker was placed on top of the abdomen of a volunteer with
direct contact to the abdominal wall whereas the simultaneously performed EGG demonstrated normal slow-wave ac-
tivity overlaid by respirational artifacts. By contrast, measurements obtained in the same subject after ingestion of the
magnetic marker into the stomach immediately showed parallel
dominant frequencies in both recordings (Fig. 11). This illustrates that the 3D-MAGMA recordings of marker movements
do not interfere with physiological or environmental magnetic
signals. Moreover, repetitive measurements in a subset of
healthy volunteers demonstrated a high reproducibility of 3DMAGMA measurements with low intra- and interindividual
variability (Table 3).
These findings underline the reliability of the main results of
our study: our data demonstrate that gastric slow waves recorded by EGG and small movements of an intragastric marker
recorded by the 3D-MAGMA system occur at the same frequency in fasting healthy volunteers. Thus, in contrast to
previous assumptions, every gastric slow wave appears to be
physiologically associated with a gastric contraction.
One possible explanation would be that the relationship
between the slow wave-generating interstitial cells of Cajal and
the smooth muscle cells of the stomach is much more complex
than currently assumed (7, 14, 25). Hypothetically, two different patterns of contraction of gastric smooth muscle cells may
exist, a minor contraction controlled by slow-wave activity and
a major contraction that needs additional neurohormonal stimulation and is controlled by spike-wave activity. Although
numerous manometric studies have not been able to identify
such a phenomenon (6, 8, 46), its existence has already been
proposed by Collard and Romagnoli (11), who performed
intraluminal manometry in patients with esophageal replacement by a remodeled (tubelike) and denervated stomach. Because of the small diameter of the remodeled stomach luminal
pressure transduction of gastric contractions is much better
than under physiological circumstances (11). In this model, the
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EGG never reached clinical acceptance. The main reason for
this was the bad correlation of EGG results with manometric
(8) or scintigraphic (3) studies. However, our observation that
gastric slow waves are directly correlated with a motor response in healthy humans may shed a new light on the
relevance of EGG studies for the understanding of gastric
physiology and gastric motor disorders. In particular, the combination of EGG and highly sensitive motility measurements
such as 3D-MAGMA may offer new insights into gastric
physiology and pathophysiology and may become a meaningful diagnostic device for important diseases such as gastroparesis, postsurgical conditions, and functional dyspepsia.
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authors observed gastric microwaves (⬍9 mmHg) and macrowaves (⬎9 mmHg) and could clearly demonstrate that the
microwaves persisted during phase I of the interdigestive
motor complex, which is conventionally defined as a period
without any contractions. Moreover, studies using a balloon
placed intragastrically (into the antrum) that were performed
by Hightower and colleagues (22, 23, 33) more than 50 years
ago had already suggested that human gastric motility shows a
fundamental basic rhythm with low-amplitude gastric contractions occurring at a frequency of ⬃3 min⫺1. However, in
contrast to our study, previous studies did not perform simultaneous EGG and motility measurements so that according to
our knowledge our study is the first to establish the association
between gastric slow-wave activity and occurrence of minute
contractions.
Theoretically, ingestion of the magnetic marker with small
amounts of water might have influenced fasting gastric motility. However, most manometric studies showed no influence of
the manometric tube and of water perfusion on fasting motility
(4, 9, 36), although tube diameter was usually much bigger
than our magnetic marker. According to one study, even a
barostat device with an intragastric balloon did not affect
gastrointestinal motility unless the balloon was inflated (34). In
addition, we were able to observe the typical resting phase of
the magnetic marker in the upper stomach after ingestion and
typical phase III-associated movements that led to evacuation
of the marker out of the stomach (20, 32). Thus interdigestive
gastric motor patterns of our healthy volunteers appeared to be
normal and unaffected by experimental procedures.
Assessment of gastric motility and gastric emptying is important for the diagnosis of gastric motor disorders, such as
gastroparesis, functional dyspepsia, and postsurgical conditions. These disorders are characterized by changes in gastric
motor function that may vary from hyper- to hypomotility,
impaired postprandial accommodation, and altered coordination of antroduodenal motility. Recognition of these characteristics may contribute to a better understanding and might offer
development of targeted treatment options. However, to date
measuring gastric motility has been restricted by the limitations
inherent in hitherto available measurement techniques.
Functional gastrointestinal disorders are an underestimated
problem in clinical practice (17). Data of countless new diagnostic systems led to the impression that disturbances of
normal gastrointestinal motility could be a major pathomechanism (31). However, precise recording of these motility disturbances is still an unsolved problem. Radiopaque markers are
used for this purpose (2, 18, 48). However, the method is
limited by the necessity to use X-rays and, thus, is not applicable for real-time measurements. To overcome the problem,
more advanced techniques were developed such as the detection of plastic tablets with a metal core by use of a metal
detector (15), the detection of 99mTc- or 111In-coated tablets by
using a double-headed gamma camera (37), or even the detection of magnetic tablets by MRI (16, 44, 45).
Numerous studies have been performed since 1980 using the
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EGG mostly physiological experiments were described (1, 19,
42), later on several investigators tried to find out clinical
relationships (26, 28, 33). Despite good technical solutions and
reliable measurements of the cutaneous EGG compared with
the EGG systems using implantable electrodes (21, 30, 38), the
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