Induction of lower esophageal sphincter (LES) dysfunction during use of the negative pressure body ventilator

Pressure measurements were recorded in the esophagus, stomach, and at the lower esophageal sphincter (LES) of 16 normal volunteers before, during, and after a period of negative pressure mechanical ventilatory assistance in an Emerson tank respirator. Esophageal pH was simultaneously measured in eight of these 16 volunteers. In 50%, the normal LES to stomach pressure gradient (which prevents reflux) was abolished during mechanical assistance of inspiration. In another 25%, it was substantially reduced, but not eliminated. The occurrence of reflux, as assessed by the level of decrease in esophageal pH, correlated significantly with the change in LES pressure. There was no evidence for gastric insufflation as a mechanism of reflux. The majority of normals studied in the tank respirator showed evidence for reflux, the mechanism seeming to be induction of lower esophageal sphincter dysfunction.