<prompt> Investigation to diagnosis of laryngopharyngeal refluxEsophageal pH monitoringDual probe impedance pH monitoringBarium esophagramScintigraphy  <response>: pH monitoring at the level of pharynx is not helpful because the acid refluxed is neutralised by the pharyngeal secretions Hence a dual bifurcated catheter measuring both pH and impedance is used across upper oesophageal sphincter thereby permitting detection of pharyngeal reflux Ref: Shackelford 8th edition Pgno: 222 