Gastroesophageal reflux disease (GERD) is a very common condition affecting up to 30% of adults. To date, therapy consists of powerful acid suppression with proton pump inhibitors (PPI). Nevertheless, only 60-70% of GERD patients report complete symptom relief with this therapy. As the mechanisms underlying symptom perception in PPI resistant patients are not fully understood, there is currently no adequate therapy available.

It is becoming increasingly clear that reflux, especially in the postprandial period, occurs from a reservoir of acid floating on top of the meal: the so-called "acid pocket". In this study, we aim to investigate further the acid pocket by determining its exact position and chemical contents between healthy volunteers, GERD patient who respond well and bad to PPI therapy and GERD patients with barrett's esophagus.

A costume made multi-pH-impedance manometry catheter will be placed in the esophagus and clipped to the Z-line. Patients then will be given a standardized meal and the position of the acid pocket will be measured. After two hours the pocket will be aspirated through a gastric catheter. Then, patients will be allowed to return home and the study will be continued for another 22 hours.

The special catheter will be removed at the end of the study. Collected acid pockets will be used to analyze content and perform permeability experiments.

Data of the 24-hour experiment will be used to evaluate the position of the acid pocket and number of reflux episodes.

Inclusion Criteria:

• signed informed consent
• older than 18 years
• fit to criteria of 'study population' (HV, PPI responder, PPI non-responder, Barrett)

Exclusion Criteria:

• pregnancy