Correspondence (letter to the editor): Diagnosis Is Difficult

The difficult diagnosis of chronic obstructive pulmonary disease (COPD) is full of traps for non-pulmonologists and is intellectually demanding in terms of its pathophysiology. For this reason, the authors deserve praise for attempting to explain this complex subject matter in as simple a way as possible. However, in my opinion, they did not succeed in doing this in Figures 3 and 4. The depicted ideal flow-volume curves are pathophysiologically shortened, as they do not relate to the absolute lung volume. This means that the influence of the increases in lung volume that cause dyspnea cannot be identified in persons with advancing disease. This insight was meant to be given by Figure 4, where the static volumes are intended to explain this problem. However, the sub-units in this figure hide any clue of how grotesquely high the total capacity is in pronounced obstruction, compared with the very low capacity in restriction. The figure legend “Note the similarity of the spirometrically measured volumes in restrictive disease and emphysema” is confusing, because this error could be avoided if the differences in total capacity were displayed.