A Pulmonary Function Study Is Performed on a 68-Year-Old Man

A pulmonary function study is performed on a 68-year-old man suspected of having emphysema.The physician requests that the study be performed to measure FRC.
Upon completion of both the helium dilution and body plethysmography it is found that the FRC obtained via body plethysmography is higher than that obtained via helium dilution.What is the probable explanation for the difference in obtained FRC values?

A) Body plethysmography overestimates FRC.
B) Helium dilution measures only the true FRC.
C) Body plethysmography measures only gas that is in communication with unobstructed airways while helium dilution measures all gas in the chest.
D) Body plethysmography measures all gas in the chest while helium dilution measures only gas that is in communication with unobstructed airways.