This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
In an emphysematous patient with bullous leison which is the best investigation to measure lung volumes? 
Select and explain. 
A. Body plethysmography, B. Helium dilution, C. Trans diaphragmatic pressure, D. DLco
A: Body plethysmography
Answer: A: Body plethysmography 
Explanation: RV ,FRC,TLC cannot measured by spirometry. This are measured by using the helium dilution technique/ body plethysmographY. In patients with severe COPD,and with large bullae in paicular,body plethysmography is preferred because the use of helium may underestimate lung volumes. Reference:Davidson's Medicine -22nd edition,page no:675