From COPD epidemiology to studies of pathophysiological disease mechanisms: challenges with regard to study design and recruitment process: Respiratory and Cardiovascular Effects in COPD (KOLIN).

: Chronic obstructive pulmonary disease (COPD) is a largely underdiagnosed disease including several phenotypes. In this report, the design of a study intending to evaluate the pathophysiological mechanism in COPD in relation to the specific phenotypes non-rapid and rapid decline in lung function is described together with the recruitment process of the study population derived from a population based study. : The OLIN COPD study includes a population-based COPD cohort and referents without COPD identified in 2002-04 ( = 1986), and thereafter followed annually since 2005. Lung function decline was estimated from baseline in 2002-2004 to 2010 (first recruitment phase) or to 2012/2013 (second recruitment phase). Individuals who met the predefined criteria for the following four groups were identified; group A) COPD grade 2-3 with rapid decline in FEV and group B) COPD grade 2-3 without rapid decline in FEV (≥60 and ≤30 ml/year, respectively), group C) ever-smokers, and group D) non-smokers with normal lung function. Groups A-C included ever-smokers with >10 pack years. The intention was to recruit 15 subjects in each of the groups A-D. : From the database groups A-D were identified; group A  = 37, group B  = 29, group C  = 41, and group D  = 55. Fifteen subjects were recruited from groups C and D, while this goal was not reached in the groups A ( = 12) and B ( = 10). The most common reasons for excluding individuals identified as A or B were comorbidities contraindicating bronchoscopy, or inflammatory diseases/immune suppressive medication expected to affect the outcome. : The study is expected to generate important results regarding pathophysiological mechanisms associated with rate of decline in lung function among subjects with COPD and the in-detail described recruitment process, including reasons for non-participation, is a strength when interpreting the results in forthcoming studies.