A physical model of the intrathoracic stomach.

To determine whether duodenogastric reflux into the thoracic stomach could be caused by the transmission of negative intrapleural pressure fluctuations into the gastric lumen, a physical model is described and an equation calculated Pm + Pa - Pmb - (Sv.Pmb.Vmb/Pm) = Ppl - Sv.Vmb where Pm is intragastric pressure, Pa is atmospheric pressure, Pmb is end-expiratory gastric base pressure, Vmb is corresponding gastric volume, Sv is stiffness of gastric wall, and Ppl is intrapleural pressure. The validity of the model is demonstrated in six anesthetized mongrel dogs (18-31 kg) in which a thoracic stomach was constructed. The transmission of the intrapleural pressure fluctuations across the gastric wall proved to be greatly influenced by the gastric stiffness. The latter parameter varied from 0.05 to 1.97 cmH2O/ml, corresponding with a pressure transmission of 100 and 60%, respectively. Because high degrees of gastric stiffness are only present for large gastric volumes or when gastric peristalsis is present, it is concluded that, in general, the intrapleural pressure fluctuations are transmitted into the thoracic stomach. For this reason, respiratory efforts may play an important role in inducing duodenogastric reflux into the thoracic stomach.