Discovery of a "Magenstrasse" and other Gastric Curiosities with a Lattice Boltzmann Model of the Human Stomach

Abstract

Mechanically, the stomach is a controlled pump that empties viscous heterogeneous liquid content from a bag (the fundus) through a sphincteric valve (the pylorus) by slow squeeze of fundic muscle. In addition, however, periodic peristaltic contraction waves travel towards the pylorus in the lower stomach (antrum), elevating pressure locally, presumably to periodically enhance emptying. My medical collaborators measured antral contractions with concurrent manometry and MRI in vivo; we analyzed the data to show that, as each antral contraction wave approaches the pylorus the pylorus momentarily closes, right when an open pylorus would have allowed a surge of fluid flow into the intestines! This is a curiosity. To study in more detail the consequences of the curious phasic relationship between the passage of antral contraction waves and pyloric opening, we applied a lattice Boltzmann computational fluid dynamics model with moving boundary conditions and a stomach geometry model parameterized using time-resolved MRI. Analysis lead to the discovery of a second curiosity the antral contraction waves produce a narrow path of emptying, or “Magenstrasse” (German for “stomach road”) that directs content from the top of the stomach to the pylorus in relatively short time with little mixing. This discovery might explain a well-known observation in pharmaceutics, that the response time of a drug after ingestion is extremely variable. (If a drug capsule opened in the stomach off the Magenstrasse, it would take over an hour for drug particles to empty into the intestine and drug to enter the circulatory system, while if release occurred on the Magenstrasse, activation time would be quick!) The fluid dynamics underlying this seemingly simple organ turns out to be surprisingly interesting.

JAMES BRASSEUR

University of Colorado Boulder