Abstract
1288
Learning Objectives 1. Review the kinetics of gastric emptying of solids. 2. Present an expanded compartment analysis to include the kinetics of gastroesophageal reflux and esophageal hang up during the course of a gastric emptying study. 3. Show how to extract kinetic constants relevant to gastric physiology using the expanded compartment model and spreadsheets. 4. Present a stochastic model to account for pulsatile gastroesophageal reflux, and contrast this model with the classic deterministic equations of the expanded compartment model.
Gastric emptying of a radio-labeled solid meal is a useful test to diagnose diseases of gastric function. In the test serial static or dynamic images are used to compute kinetic parameters relevant to gastric physiology. The most general model is a modified exponential function (1): A(t) = (1 - (1-exp(-kt))α) Where A(t) is the fraction of activity left in the stomach at time t; k is a constant to describe gastric emptying; and α describes either a lag phase (α > 1) or accelerated emptying beyond exponential (α < 1). In the presence of gastroesophageal reflux or hang up this equation is inadequate to evaluate gastric physiology. Instead a new set of equations is necessary, and these can be constructed from a kinetic model based on an analysis that includes the esophagus, stomach, and bowel as compartments. These equations show that a single region of interest that includes the esophagus and stomach is adequate to extract gastric parameters when esophageal hang up is short-lived. However, when gastroesophageal reflux is present such region of interest is not enough. Moreover, to account for a pulsatile reflux it is necessary to replace the deterministic equations of the compartment model with stochastic equations that model the pulsations as a random variable.