Anand P. Tamhankar, Jeffrey H. Peters, Giuseppe Portale, Chih-Cheng Hsieh, Jeffrey A. Hagen, Cedric G. Bremner, Tom R. DeMeester, University of Southern California, Los Angeles, CA

Aim: Proton pump inhibitors are the mainstay of medical management in gastroesophageal reflux disease. Though they provide symptomatic relief, reflux may persist. We hypothesize that omeprazole does not reduce the total amount of gastroesophageal reflux, but simply alters its pH characteristics. Methods: Six asymptomatic volunteers had combined 24hr impedance-pH monitoring before and after seven days of omeprazole (20mg bid). All subjects had a normal barium esophagogram, motility and 24 hr pH studies. Multichannel intraluminal impedance was used to identify reflux episodes, which were classified as acid (pH < 4), weak acid (pH > 4, but drop >1 pH unit) and non-acid (pH > 4 & drop <1 pH unit) by pH measurements five cm above the lower esophageal sphincter (LES). The duration of the reflux episodes was measured at the same level by impedance. A gastric pH sensor located 10cm below the LES was used to verify the action of omeprazole. Data were compared using Wilcoxon matched pairs test and Fisher's exact test. Results: Impedance detected a total of 116 reflux episodes before and 96 after omeprazole treatment. The median number of reflux episodes per subject was similar before and after omeprazole therapy (18 vs 16, p=0.4). The total duration of reflux episodes was also similar (1637 seconds before vs 2548 seconds after omeprazole, p=0.5). The median duration of reflux episodes per subject was again similar (287.6 vs 220.1 seconds, p=0.5). However, the proportion of acid reflux episodes was reduced from 62.9% before to 2.1% after omeprazole (p<0.0001). Following omeprazole therapy, the proportion of non-acid reflux episodes increased (14.6% to 76%, p<0.0001) corresponding to the reduction of acid reflux episodes, while the proportion of weak acid reflux episodes did not change (22.4% to 21.8%, p=1.0). The combined proportion of non-acid and weak acid reflux episodes increased from 37.1% to 97.9% (p<0.0001). Conclusions: Combined 24 hour impedance-pH monitoring showed that omeprazole treatment does not impact the number of reflux episodes or their duration. Omeprazole does convert acid reflux to less acid reflux. These findings have a profound impact on our understanding of the treatment of gastroesophageal reflux disease.