BACKGROUND:~Background. COPD is a common chronic health condition. Because current medical treatments have minimal impact on disease progression, a strategy to prevent COPD-related disability would have important clinical and public health benefits.~DESIGN NARRATIVE:~The study will test a specific conceptual model of how disability develops in COPD. The aims are: (1) To evaluate the impact of respiratory impairment, especially pulmonary function impairment, on the risk of functional limitation in COPD. Using a control group, to elucidate the prevalence of respiratory impairment, functional limitation, and disability that is directly attributable to COPD. (2) In adults with COPD, to delineate the longitudinal effect of functional limitation on the risk of incident disability. The investigators hypothesize that development of functional limitation, and not pulmonary function impairment, is the major determinant of disability. (3) To determine the prospective impact of disability on the risk of future adverse health outcomes. The investigators will assemble a prospective cohort of 1200 randomly sampled adults with COPD who are members of a large regional health maintenance organization. A matched control group of 300 subjects will be recruited. Subjects will undergo a detailed physical assessment that measures respiratory impairment (e.g., pulmonary function) and functional limitation (e.g., lower extremity function, muscle strength, exercise performance, and cognitive function). Structured telephone interviews will ascertain disability outcomes at baseline and 18-month prospective follow-up. The investigators will also study the modulating effects of specific risk factors and protective factors on the progression from functional limitation to COPD-related disability, including psychological factors, environmental exposures, and health care process factors.
To test a conceptual model of how disability develops in chronic obstructive pulmonary disease (COPD).