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Background: 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.

Method: The OLIN COPD study includes a population-based COPD cohort and referents without COPD identified in 2002–04 (n = 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 FEV₁ and group B) COPD grade 2–3 without rapid decline in FEV₁ (≥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.

Results: From the database groups A–D were identified; group A n = 37, group B n = 29, group C n = 41, and group D n = 55. Fifteen subjects were recruited from groups C and D, while this goal was not reached in the groups A (n = 12) and B (n = 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.

Conclusion: 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.

The Global Lung Function Initiative (GLI) has recently published international reference values for diffusing capacity of the lung for carbon monoxide (DLCO). Lower limit of normal (LLN), i.e. the 5th percentile, usually defines impaired D-LCO. We examined if the GLI LLN for D-LCO differs from the LLN in a Swedish population of healthy, never-smoking individuals and how any such differences affect identification of subjects with respiratory burden. Spirometry, D-LCO, chest high-resolution computed tomography (HRCT) and questionnaires were obtained from the first 15 040 participants, aged 50-64 years, of the Swedish CArdioPulmonary bioImage Study (SCAPIS). Both GLI reference values and the lambda-mu-sigma (LMS) method were used to define the LLN in asymptomatic never-smokers without respiratory disease (n=4903, of which 2329 were women). Both the median and LLN for D-LCO from SCAPIS were above the median and LLN from the GLI (p<0.05). The prevalence of D-LCO <GLI LLN (and also <SCAPIS LLN) was 3.9%, while the prevalence of D-LCO >GLI LLN but <SCAPIS LLN was 5.7%. Subjects with D-LCO >GLI LLN but <SCAPIS LLN (n=860) had more emphysema (14.3% versus 4.5%, p<0.001), chronic airflow limitation (8.5% versus 3.9%, p<0.001) and chronic bronchitis (8.3% versus 4.4%, p<0.01) than subjects (n=13 600) with normal D-LCO (>GLI LLN and >SCAPIS LLN). No differences were found with regard to physician-diagnosed asthma. The GLI LLN for D-LCO is lower than the estimated LLN in healthy, never-smoking, middle-aged Swedish adults. Individuals with D-LCO above the GLI LLN but below the SCAPIS LLN had, to a larger extent, an increased respiratory burden. This suggests clinical implications for choosing an adequate LLN for studied populations.

Background: Interstitial lung abnormalities (ILA) are incidental findings on chest computed tomography (CT). These patterns can present at an early stage of fibrotic lung disease. Our aim was to estimate the prevalence of ILA in the Swedish population, in particular in never-smokers, and find out its association with demographics, comorbidities and symptoms.

Methods: Participants were recruited to the Swedish CArdioPulmonary BioImage Study (SCAPIS), a population-based survey including men and women aged 50–64 years performed at six university hospitals in Sweden. CT scan, spirometry and questionnaires were performed. ILA were defined as cysts, ground-glass opacities, reticular abnormality, bronchiectasis and honeycombing.

Findings: Out of 29 521 participants, 14 487 were never-smokers and 14 380 were men. In the whole population, 2870 (9.7%) had ILA of which 134 (0.5%) were fibrotic. In never-smokers, the prevalence was 7.9% of which 0.3% were fibrotic. In the whole population, age, smoking history, chronic bronchitis, cancer, coronary artery calcium score and high-sensitive C-reactive protein were associated with ILA. Both ILA and fibrotic ILA were associated with restrictive spirometric pattern and impaired diffusing capacity of the lung for carbon monoxide. However, individuals with ILA did not report more symptoms compared with individuals without ILA.

Interpretation: ILA are common in a middle-aged Swedish population including never-smokers. ILA may be at risk of being underdiagnosed among never-smokers since they are not a target for screening.