Fig. 1.

Comparison of the effects of free air and bagged air on the upper esophageal sphincter (UES) in unthoracotomized animal. We found that injection of air in the proximal stomach caused the transient upper esophageal sphincter relaxation (TUESR), but injection of two times that volume of bagged air had no effect on the UES. Therefore, the stimulus for activation of TUESR is gas escape from the stomach and not gastric distension. Note also the rapid increase in gastric perfusion pressure (*) associated with the TUESR. TH, thyrohyoideus; CP, cricopharyngeus; CT, cricothyroideus.