We are afraid the implementation of the present study results in the clinical setting might be limited. In fact, the main reason for measuring lung volumes in subjects with COPD is to determine the presence and degree of lung hyperinflation. To the radiologist, hyperinflation of the lungs implies an increase in total lung capacity (TLC) because this is the lung volume at which chest radiographs are normally obtained. In a clinical context, however, hyperinflation implies an abnormal increase in the volume of gas in the lungs at the end of tidal (functional residual capacity [FRC]) or maximal (residual volume [RV]) expiration.2 Moreover, hyperinflation is sometime inferred from an increase in the RV/TLC (Motley index) and the FRC/TLC ratios, commonly used as a surrogate of air trapping. Unfortunately, the authors do not mention any of these other parameters in their study. This is, in our opinion, a major concern because TLC in COPD patients varies as a function of the prevalent phenotype (increased in emphysema, often normal in chronic bronchitis); therefore, it cannot be used routinely to address pulmonary hyperinflation in COPD. Conversely, RV and FRC are strongly related to the severity of airflow obstruction.