Factors that influence induction of gastroesophageal reflux in normal human subjects

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Abstract
Findings from recent studies indicate that transient relaxation of the lower esophageal sphincter (LES) is an important contributory mechanism to spontaneous episodes of gastroesophageal reflux (GER) in normal subjects as well as in patients with reflux esophagitis. Our study aim was to evaluate the interrelationship between reduction of LES pressure and elevation of intraabdominal pressure in the induction of GER in healthy subjects. Seven volunteers were studied supine after gastric loading with 0.1 N HCl. A pH probe recorded acid GER. Leg raising (LR) or abdominal compression (AC) were used as stress maneuvers to increase intraabdominal pressure, either alone or in combination with stimuli that concurrently lowered LES pressure, namely multiple rapid swallows (RS) or intraesophageal balloon distention (BD). Each individual stimulus and stimulus combination was tested three times, giving a total of 24 test maneuvers per subject. The test maneuvers elicited 2–12 GERs in each subject. The GER incidence for single maneuvers was: AC, 0%; LR, 0%; RS, 19%; and BD, 24%. LR in combination with RS or BD did not increase the incidence of GER above that induced by RS or BD alone. In contrast, AC concurrent with RS and BD increased the incidence of GER to 52% and 81%, respectively. For all test conditions, a prerequisite for the occurrence of GER was a fall in LES pressure to a minimal value of 3 mm Hg or less. GER never occurred when LES pressure was ≥4 mm Hg, even during intervals of increased intraabdominal pressure. We conclude that (1) virtually complete absence of LES pressure is an essential prerequisite for the induction of GER; (2) during intervals of negligible LES pressure, elevation of intraabdominal pressure increases the prevalence of GER;and (3) LR by normal subjects induces a substantial increase in the abdominal pressure but does not increase GER, probably due to a pinch-cock effect of the diaphragmatic hiatus on the intrahiatal esophageal segment.