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Use Of Autocorrelation To Improve The Three Dimensional Plot Of Transcutaneous Human electrogastrograms
Abstract
Transcutaneous human electrogastrograms (EGG) have been recorded for many years without significant improvement in their interpretation. The application of amplitude or power spectrum analysis is a powerful method to analyse EGG signals which have a relatively narrow frequency band and infralow fundamental frequencies (0.03-0.1 Hz) . Three dimensional plots are often used to represent the dynamics of the amplitude or power changes in the EGG signals vs. frequency and time. Because of the movement and respiratory artifacts three dimensional plots are not always clear enough to allow further interpretation of the results. In this paper we address that problem suggesting three dimensional plot of the autocorrelated EGG signals. The proposed method minimizes the influence of the artifacts and provides both repeatable results and good possibilities for interpretation.
Cutaneous recordings of gastric electrical activity (electrogastrography (EGG)) could become a valuable non-invasive tool for recognising gastric electrical abnormalities. Although signals obtained with internally implanted electrodes deliver quantitative information, this technique cannot be used for diagnostic purposes because of its invasive nature. On the other hand, the objectivity of electrogastrography is still in question. The aims of this work are to develop computer techniques for extracting quantitative information from digital electrogastrograms, and to evaluate quantitatively EGG recordings from healthy volunteers. The dynamics of all four EGG parameters are studied: amplitude, frequency, time shift between different channels, and waveform. Four separate two-dimensional computer plots are developed using specially designed digital signal-processing procedures. Each parameter is evaluated in a study of 20 healthy volunteers. Frequency is found to be the only EGG parameter that shows quantitative consistency and merit.
The recording of gastric myoelectrical activity by means of cutaneous electrodes attached to the external abdominal wall is
termed electrogastrography. Respiration and motion artefacts hamper the interpretation of electrogastrographic signals. Running
spectrum analysis, using the fast Fourier transform, seems to provide a concise spectral representation of electrogastrographic
data. In this paper the concept of running spectrum analysis is presented in detail using test signals consisting of frequency
modulated sine waves and actual recordings from dog and man. Especially the visual interpretable representation in appropriate
plots is emphasised and discussed. It is demonstrated that tachygastrias with a duration of the order of 30s can easily be
recognised in the spectra. In most cases the gastric frequency can be recognised in the spectra. It is concluded, therefore,
that running spectrum analysis has to be considered an attractive noninvasive method to study gastric myoelectrical activity
in dog and man.
A fast algorithm has been worked out for performing the Discrete Hartley Transform (DHT) of a data sequence of N elements in a time proportional to Nlog 2 N. The Fast Hartley Transform (FHT) is as fast as or faster than the Fast Fourier Transform (FFT) and serves for all the uses such as spectral analysis, digital processing, and convolution to which the FFT is at present applied. A new timing diagram (stripe diagram) is presented to illustrate the overall dependence of running time on the subroutines composing one implementation; this mode of presentation supplements the simple counting of multiplies and adds. One may view the Fast Hartley procedure as a sequence of matrix operations on the data and thus as constituting a new factorization of the DFT matrix operator; this factorization is presented. The FHT computes convolutions and power spectra distinctly faster than the FFT.
Interpretation of Computer Processed Electrical Signals from the Gastro-Intestinal Tract
- Y J Kingma
- M M Chambers
- K L Bowes
- C Bannister