 The pH-MII device in use for this study Comfortec pH-MII Sandhill Scientific is a nasogastric probe with seven rings, composed by six dipolar impedance channels and one antimony electrode responsible for pH detection and placed in the middle of the distal impedance dipole. Due to these characteristics, pH-MII is able to measure the esophageal height reached by refluxate and to identify the direction of esophageal bolus movements, thereby distinguish between a retrograde flow reflux and an anti-retrograde flow swallow. 