Fig. 1
From: Validation of a method to assess emphysema severity by spirometry in the COPDGene study
Distribution of the COPDGene population according to CT derived metrics: total expiratory gas trapping (y-axis, %LAA-856exp) and functional gas trapping (x-axis, %fLDA). Data points are colored according to the corresponding ESI values calculated by spirometry (progressive range 0–10). Total expiratory gas trapping entails the air trapped in the lungs at the end of a forced expiration due to both conductive airway disease (functional gas trapping, %fLDA) and emphysematous parenchymal destruction, whose amount is represented by the ESI values