Electrogastrography : signal analytical aspects and interpretation

Electrogastrography is defined as the recording of the myoelectrical activity of the smooth muscles of the stomach by means of cutaneous electrodes attached to the abdominal skin. The recorded signal is called ~n electrogastrogram. On October 14, 1921, Walter Alvarez attached two electrodes to the abdominal skin of a 'little woman' and connected the leads to a very sensitive string galvanometer. The abdominal skin was so thin that gastric peristalsis was easily visible. The repetition frequency of the sinusoidal configuration of the recorded potential variations, being 0.05 Hz, corresponded to the repetition frequency of the gastric waves passed by, proving the gastric origin of the electrical signal. Alvarez stated: 'The first human electrogastrograms are here presented' (Alvarez, 1922). However, he never succeeded in deriving electrogastrograms from other persons. All the same he may be considered to be the pioneer in the study of myoelectrical and mechanical behaviour of the stomach endowed with great prophetic gifts. Most of his observations predominantly made from recordings derived with electrodes attached to the serosal wall of the stomach in test animals (which he denoted also electrogastrograms) command great respect since in our eyes only primitive equipment was available. From literature it seems that little progress has been made concerning the myoelectrical activity of the stomach until the sixties. About that time, when improvements in electronics made recordings much easier to perform, an enormous increase in interest in this topic occurred, resulting in a vast amount of publications. Many of the findings of Alvarez have been rediscovered by other investigators. The reason for this conspicuous interest arose from the growing notion that the myoelectrical activity of the stomach plays a dominant role in controlling gastric functions, more or less similar to the electric activity originating in the sino-atrial node does in the heart. It was felt to be reasonable at that time to expect that gastric motility disorders would be accompanied by a disturbance of the electrical activity and that the electrical activity would therefore be of a diagnostic significance

Onderzoek naar veldwerk bij aardrijkskunde in het vmbo

Deze bijdrage geeft een korte tussenstand van een promotieonderzoek naar veldwerk aardrijkskunde in het vmbo. Na een beknopte bespreking van belangrijke literatuur over veldwerk worden enkele resultaten van een vragenlijst over veldwerk onder aardrijkskundedocenten gepresenteerd. De focus ligt echter op een van de eerste stappen van een ontwerponderzoek waarbij samen met vmbo docenten aardrijkskunde getracht is veldwerk zo op te zetten dat er meer diepgang in het leren van leerlingen plaats vindt