Assessment of gastric accommodation and gastric emptying using 3D- and Duplex ultrasonography

Abstract

The stomach plays a crucial role in the digestion process. It is therefore not surprising that inadequate function of the stomach may induce upper abdominal symptoms, which are highly prevalent in the western society. Over the years the secretory function and more recently the grinding function of the stomach have been studied extensively and the capacity of the stomach to store and to transport food from the proximal to the distal stomach received growing attention. The mechanical process underlying this typical function is termed gastric accommodation and is described as the response that provides the reservoir function by lowering gastric tone and thereby affecting intragastric distribution of the meal. The tone of the proximal stomach is adjusted in such a way that antral filling is kept constant until the meal has emptied from the stomach. The distal part, so-called antrum, of the stomach is responsible for the grinding of the food to a particle size of about 2 mm. When food particles reach this size gastric emptying is initiated in a pulsatile rather than a constant fashion. To date, it is not entirely clear which factors contribute to the initiating of the accommodation response after meal ingestions. The gold standard for measuring gastric accommodation is the barostat, however it involves placement of an intragastric bag, which might influence gastric physiology. This thesis describes two non-invasive methods, 3D ultrasonography and Duplex ultrasonography to measure gastric volume and gastric emptying. First of all it has been demonstrated that the barostat technique influences normal physiology. Postprandial the barostat bag causes dilatation of the antrum, due to meal displacement without influencing early gastric emptying. This antral dilatation is likely to induce exaggerated proximal gastric relaxation. Furthermore, we have demonstrated that 3D ultrasonography is a feasible non-invasive technique to measure gastric volumes and demonstrates a distinct overlap with barostat data in healthy subjects and functional dyspepsia. Secondly we have shown that the gastric antrum plays an important role in the generation of gastrointestinal symptoms in healthy volunteers and patients with functional dyspepsia. Fullness is related to antral volume and area rather than proximal volume and therefore the gastric antrum may play a key role in normal appetite regulation. Using Doppler ultrasonography we have demonstrated that gastric emptying of a low-and high-caloric liquid nutrient occurs both during peristaltic and nonperistaltic antral activity. Furthermore only low gradients are necessary tot generate transpyloric flow. All results presented provide new insights in the physiology and pathophysiology of gastric motor and sensory behavior and addresses a new technique and point of view in the challenge to unfold the mystery of the pathophysiological mechanisms that lead to functional dyspepsia.