Pathophysiology of Restrictive Procedures

Abstract

There are three different types of restrictive surgical procedures for morbid obesity: vertical banded gastroplasty (VBG), adjustable gastric banding (AGB), and sleeve gastrectomy (SG). These procedures are currently realized via laparoscopy. The mechanism of VBG is related to the size of the gastric pouch and to the calibrated outlet. After a solid meal, patients describe a sensation of fullness and satiety or even epigastric or low-retrosternal discomfort, indicating pouch fullness; at this point the patient must stop eating. If eating continues, discomfort increases until voluntary or spontaneous regurgitation of the excess food occurs. Satiety is dependent on the thickness and consistency of the food eaten; hence patients who consume mainly liquids usually have less weight loss. Gastric motility may play a part in the rate of drainage of the gastric pouch, and excessive motility may be responsible for poor weight loss in some cases. The variability in weight loss after gastroplasty and other restrictive procedures highlights the fact that the final amount of weight loss depends on patient-controlled factors as well as on the surgical procedure. Following placement of laparoscopic AGB (LAGB), as soon as the patient ingests two spoonfuls the small gastric compartment above the band is filled and he or she experiences a feeling of fullness. Since it takes a long time for this compartment to empty because of the narrowed stoma, more food can be ingested only after substantial time has elapsed. The patient must therefore eat at a much slower pace, and this slower pace allows the satiety center to be stimulated. As the hunger sensation is no longer present, overall food intake is reduced. The major advantage of LAGB is the possibility to adjust the size of the outlet. Another hypothesis not confirmed as the mode of action of gastric banding was gut hormone modulation. The mechanism of action of laparoscopic SG (LSG) is not only the restriction obtained by resecting part of the body and the entire fundus of the stomach, leaving a small gastric tube of 100–150 ml. Hormonal changes following this procedure must also be considered. Ghrelin is a 28-amino-acid orexigenic peptide, secreted essentially by the fundus of the stomach, which stimulates feeding behavior and hunger. In LSG, the gastric fundus is resected and plasma ghrelin levels are expected to decrease following surgery. Another mechanism explaining weight loss after LSG could be the relationship between appetite and gastric emptying, as the gastric clearance seems to be improved.