Measuring functional performance in patients with COPD: a discussion of patient-reported outcome measures

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Abstract
Background: Chronic obstructive pulmonary disease (COPD) is a chronic condition and a major public health concern. Moreover, its prevalence is increasing. COPD commonly affects patient performance of daily activities that people perform in order to meet basic needs, fulfill usual roles, and maintain their health and well-being. What types of activities are affected and to what degree≟ How do these effects change over time? What impact, positive or negative, do various treatments have on the capacity of patients to perform activities? To address these questions, the concept of activity performance must be defined and appropriately measured. Methods: This paper presents a model of function that defines functional performance as distinct but related to physiological impairments and functional capacity. A systematic review of the literature was conducted to locate patient-reported outcome (PRO) instruments that have been used to capture functional performance in clinical studies of COPD and have been validated with patients with COPD. The content of each measure was reviewed to assess depth and breadth of coverage. Results: The systematic review yielded nine validated PROs used to capture functional performance in clinical studies of COPD: three are generic; six were designed specifically for use in patients with COPD. Variability in content coverage occurred across the PROs, with some sacrificing depth for breadth. Few of the PROs covered the full range of content as defined in the model. Limiting selected PROs to those that have been used with patients with COPD, while relevant to this population, may preclude other PRO instruments that can measure functional performance. The relevance of another instrument would, however, need to be confirmed with patients with COPD. Conclusions: Selection of endpoints and instruments for clinical studies of COPD and its treatment must be driven by a clear definition of concepts of interest and the relevance of content areas to patients. Some existing instruments may provide adequate coverage of endpoints or content areas under investigation. Others clearly will not.