To the Editors:
Because forced expiratory volume in 1 s is a poor descriptor of chronic obstructive pulmonary disease (COPD) heterogeneity [1], interest has emerged regarding the identification of clinically relevant COPD phenotypes [2, 3]. We recently reported the usefulness of applying mathematical models (i.e. principal component and cluster analyses) to multiple variables for the identification of clinical phenotypes in a cohort of COPD subjects [4]. These original analyses allowed the description of four COPD groups, which we called “clinical COPD phenotypes” [4]. This terminology was based on the classical definition of “phenotype”, referring to the observable characteristics (including respiratory manifestations and comorbidities) of patients. Recently, a panel of experts proposed the following modified definition for clinical COPD phenotypes: “a single or combination of disease attributes that describes differences between individuals with COPD as they relate to clinically meaningful outcomes (symptoms, exacerbations, response to therapy, rate of disease progression, or death)” [2 …
