In an emphysematous patient with bullous leison which is the best investigation to measure lung volumes?

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