Effects of posture on the physiology of gastric emptying: A magnetic resonance imaging study

Abstract

The stomach maintains the rate of gastric emptying despite radical changes in body position and intragastric distribution of gastric contents. In SP, hydrostatic pressure (modulated by gastric tone) dictates the gastric emptying. In UDP, gastric emptying also appears to be mediated by continuous adaptation of gastric tone. These findings provide support for the hypothesis that the mechanism of gastric emptying resembles a "pressure pump" rather than a "peristaltic pump". Institute of Diagnostic Radiology, University Hospital Zurich, Switzerland Abstract Objective. Gastric contents empty from the stomach despite frequent changes in body position. The mechanism that maintains gastric emptying independent of position is poorly understood. The aim of this study was to determine the effects of body position on gastric emptying and motor function. Material and methods. Twelve volunteers were investigated in seated position (SP) and upside-down position (UDP) after ingestion of 300 ml water. Magnetic resonance imaging provided a non-invasive assessment of gastric emptying and volumes, intragastric distribution and peristaltic function. Results. A marked difference in distal/proximal intragastric distribution between UDP and SP was present (7% versus 40%; pB/ 0.01). Gastric-emptying time was similar but emptying pattern was linear in UDP and exponential in SP. Peristalsis was slower in UDP than SP (2.75 versus 2.96 min (1 ; pB/ 0.01), but no correlation was found between peristaltic frequency and the rate of gastric emptying in either position. Postprandial volume response (gastric relaxation) was greater in UDP than SP (280 versus 250 ml; p B/ 0.05). A correlation was found between gastric relaxation and gastricemptying time in SP (r 2 0/0.46) but not in UDP. Conclusions. The stomach maintains the rate of gastric emptying despite radical changes in body position and intragastric distribution of gastric contents. In SP, hydrostatic pressure (modulated by gastric tone) dictates the gastric emptying. In UDP, gastric emptying also appears to be mediated by continuous adaptation of gastric tone. These findings provide support for the hypothesis that the mechanism of gastric emptying resembles a ''pressure pump'' rather than a ''peristaltic pump''.

Effect of meal volume and calorie load on postprandial gastric function and emptying: studies under physiological conditions by combined fiber-optic pressure measurement and MRI

“…MRI studies under physiological conditions and after pharmacological modulation of gastric activity have shown that the magnitude of this postprandial relaxation is closely associated with the gastric emptying rate of water and liquid nutrients (20,22). In contrast, the frequency and vigor of antral contractility did not affect this process (20,22,23,34). These findings suggest that gastric emptying is driven by tonic contraction of the gastric fundus, the so-called "pressurepump" hypothesis of gastric emptying (20).…”

Antral recirculation in the stomach during gastric mixing

“…A number of studies have been conducted to clarify the functions of the stomach, particularly focusing on the emptying of gastric contents in the duodenum via the pylorus (13,15,16,17,23). Because changing posture or the ingested volume alters the content location in the stomach, the effects of these parameters on gastric emptying have also been studied extensively (2,4,7,9,14,30). However, even with advances in medical imaging techniques (11,25), visualization of gastric flow is still a difficult task, in particular, with regards to studying gastric mixing in detail.…”

Microgravity Simulated by the 6° Head-Down Tilt Bed Rest Test Increases Intestinal Motility but Fails to Induce Gastrointestinal Symptoms of Space Motion Sickness

“…Of note, no changes in gastric emptying could be detected using a 13 C breath test. Since 13 C breath test compares well with the gold-standard scintigraphy [3,5,7,8,23,32], especially for healthy individuals ( [11] and many other studies), our results exclude marked changes in gastric emptying upon HDT [31,35].…”