High-pass filtering of the electrogastrogram

Compressed time and frequency recording of the electrogastrogram by individual wave detection

Electrogastrography (EGG) is a method for recording and analysis of the bioelectrical activity of the stomach, acquired by cutaneous electrodes. The problem of obtaining an EGG signal as free of artefact as possible has recently found some solutions. Good quality recordings of several hours duration can be acquired, often needed, especially if clinical applications are envisaged. Therefore, a next problem to be considered would be time-compressed presentation of the EGG signal without loss of relevant signal characteristics. Relative amplitude changes can be of clinical value, while frequency variations are traditionally regarded as more important. A method for simple compressed presentation of long term EGG recordings, without losing information about the real amplitude and/or frequency changes or transients, is presented. It makes use of detection of successive wave extrema in an EGG. Successive wave amplitudes and durations are measured and momentaneous frequencies are derived. Then a compressed two-trace plot is generated, representing amplitude and frequency variations with respect to time. The method is virtually insensitive to baseline drift, as only the peak amplitudes are detected and followed. A compression factor with respect to the traditional signal recording (1 cm min(-1) or 2 cm min(-1) paper speed) of 5 up to 15 per trace can be obtained.