Function of the gastric band
Positioning the band horizontally (horizontal gastroplasty) at the beginning of the stomach (cardiac) separates it into a small pouch and the large main stomach. The pouch exit is referred to as a gastrostoma. It prevents the premature passage of food portions, radically reduced in size due to the limited volume of the small pouch, thus limiting the stomach’s massive intake capacity. On one hand, reduced food intake is achieved by the reduction of meal portions and the mechanically obstructed passage into the main stomach, and on the other, by the following mechanism: by stimulating stretch receptors in the stomach wall by filling the pouch, "stomach full" is signalled to the brain by afferent (towards brain) signals not yet fully understood. These signals will then be processed by the brain as "satiation." Stretching of the pouch can only occur if the so-called oesophageal sphincter (muscle-augmented part of the oesophagus right above the stomach entrance) is sufficiently functional, meaning it closes tightly enough to avoid regurgitation (reflux of food mush from the stomach to the oesophagus). With mechanical restrictions alone, the patient would keep on eating until vomiting. If the lower oesophageal muscle is too weak, the regurgitations and lack of a sensation of satiety may cause a "substitute stomach" to be created by progressive dilatation (extension) of the oesophagus, with a similar clinical indication as achalasia (comparable to cardiospasm). Over time this is observed in only a few patients.
Since sensation of satiety is a subjective factor, it may be perceived at different levels after surgery just as it is before surgery. Often patients will have to learn to deal with it after the band has been inserted. If the sensation of satiety is insufficient, the patient may be conditioned to recognise the right time to stop by the repeated unpleasant experience of vomiting. According to its functional principle and to prior experience in gastroplasty, the pouch size should be as small as possible (15ml), to keep meal sizes small and to avoid stretching of the pouch. By its general functional principle the gastric band requires intact mastication, and thus a flawless denture, since insufficiently chewed food will not pass the gastrostoma.
Remarkable progress has been made in the adjustability of the gastrostoma size, which is guaranteed at any given time, and thus control over food intake by a reservoir (injection reservoir, port system) positioned either on the abdominal wall or the costal arch, which is connected to the band via a catheter. Utilising a specific puncture needle, the reservoir may be punctured through the patient’s skin and inner diameter of the stomach band can be adjusted by injecting liquid (fig. 7). The gastric band is only tightened after a period of osseous integration (6 weeks) has passed, and then it is done in several steps. The band is adjusted in relation to the individual weight progress and according to meal sizes. If for example the stoma should shift, unrelated surgery should become necessary, or a pregnancy occurs, etc., the gastric band can be opened very easily.
- Fig.7: Constricting the gastric
band (adjusting)
Salt solution is injected into the reservoir with a syringe (A). Thus the band’s "balloon" is filled and the inner diameter reduced.