Application to biomedical signals - Practical Biomedical Signal Analysis Using MATLAB - page 218

The contemporary EMG diagnosis is largely based on the disease-specificdiffer-
ences in MUAP shapes which cannot be detected even by the most sophisticated
methods of sEMG detection and processing due to the information loss caused by
volume conduction. We can conclude therefore that at the moment surface EMG
cannot replace needle EMG in diagnostic applications. However, sEMG is able to
provide additional information, e.g., on MU size and topography or conduction ve-
locity, which is complementary to the routine EMG diagnostic techniques [Merletti
et al., 2008]. One of the most important advances in the sEMG field is the increas-
ing possibility of extracting individual MUAPs from non-invasive recording. With
the improvements in sensor design and further development of processing methods
high resolution surface EMG may become in the near future a widespread tool for
investigation of muscle function at the individual unit level.
4.4 Gastro-intestinal signals
An electrogastrogram (EGG) is a recording of electrical activity of stomach; an
electroenterogram (EEnG) is a recording of both stomach and intestine electrical
activity. EEnG in humans is recorded from three or more Ag-AgCl electrodes placed
on the abdominal surface. Similarly, magnetogastrogram (MGG) is a record of the
magnetic field generated by the electric field of the stomach; and magnetoenterogram
(MEnG) corresponds to the magnetic field generated by the gastro-intestinal tract.
EGG and EEnG reflect the electrical activity of the smooth muscles of the gastro-
intestinal tract, which drive the peristaltic movements. The patterns of electrical ac-
tivity of EEnG consist of slow wave and superimposed action potentials generated
by pacemakers—the interstitial cells of Cajal. The frequencies of slow waves change
along the gastro-intestinal tract. They are respectively: in stomach—0.03-0.07 Hz,
in large intestine 0.01-0.03 Hz, in ileum 0.07-0.13 Hz, in jejunum 0.13-0.18 Hz, in
duodendum 0.18-0.25 Hz. In Figure 4.58 spectra presenting rhythms of different
parts of the gastro-intestinal tract and their time fluctuations are shown.
The gastric and intestinal slow wave is present even during quiescent periods.
When smooth muscle contraction occurs, spike potentials phase locked to it appear.
Abnormality in the rhythmic electrical activity generation is called gastric dysrhyth-
mia. In EGG the deviations from normal rhythm (3 cycles/minute) include brady-
gastria and tachygastria. Bradygastria involves a decreased rate of electrical activity
in the stomach, below 2 cycles/minute for at least 1 minute. Tachygastria is con-
nected with an increased rate of electrical activity above 4 cycles/minute for at least
1 minute. Dysrhythmic activities in the gastro-intestinal tract may lead to a variety of
disorders such as gastroparesis, functional dyspepsia, and gastro-oseophageal reflux
disease.
Although the first human EGG was recorded by Alvarez more than 80 years
ago [Alvarez, 1922], the lack of standardized methodology in terms of electrode