This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardio thoracic surgery  , Subject name: Anatomy
Investigation to diagnosis of laryngopharyngeal reflux 
Select and explain. 
A. Esophageal pH monitoring, B. Dual probe impedance pH monitoring, C. Barium esophagram, D. Scintigraphy
B: Dual probe impedance pH monitoring
Answer: B: Dual probe impedance pH monitoring 
Explanation: 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