PROTOCOL After an overnight fast volunteers will come to the endoscopy unit of the UZ Gasthuisberg, where the study will be performed. At the beginning of the study, the solid-state manometric catheter consisting of 36 manometry channels at 1cm intervals and 16 impedance channels (Medical Measurement Systems, Enschede, The Netherlands) will be placed transnasally under topical anesthesia and will be positioned along the esophagus. Manometry will measure pressure in the esophageal body, and the LES and the upper part of the stomach. The impedance channels are used to measure bolus movement. After the catheter is positioned in the esophagus the volunteer will remain in a bed, in semi-recumbent position for the entire study period. HRM and impedance will be recorded for approximately 2 hours.