The research project CHAIN (COPD Assessment History in Spain): "A Multidimensional Study on the Evolution of Chronic Obstructive Pulmonary Disease (COPD)is a multicentre, observational study conducted in several areas of Spain aimed to better define COPD natural history and its phenotypes

Observational studies are needed to ascertain the natural history and progression of COPD, and to better define its phenotypes. These two aspects are considered fundamental to a proper evaluation of current (and future) COPD treatment options, and it could possibly justify the limited impact of recent major drug trials.

Currently, there remain gaps in the natural history of patients with COPD. Most data are from analysis of mild COPD patients or smokers, usually measuring only fall in FEV1, and both have significant limitations in design and interpretation.

Studies in more severe patients with COPD have also been conducted mainly by studying lung function, possibly influenced by the recommendations of current guidelines for disease management. In recent years, we have more longitudinal data on changes in exercise capacity, imaging, and biomarkers, among other variables of interest, but our knowledge is yet partial.

The research project CHAIN (COPD Assessment History in Spain): "A Multidimensional Study on the Evolution of Chronic Obstructive Pulmonary Disease (COPD) is a multicenter observational study that will follow prospectively two cohorts: a) a COPD group active or former smokers (COPD cohort) and b) a group of active smokers or former smokers without COPD (control cohort). Both cohorts will be followed up for a period of at least 5 years, with visits every 12 months (and phone controls at least every 6 months). We will try to extend the monitoring of the cohort up to 10 years. CHAIN is supported by the PII of COPD SEPAR

Inclusion Criteria:

• Patients ≥ 35 years.
• Diagnosis of COPD (GOLD PBD FEV1/FVC ratio <0.70).
• Being in a stable phase of disease (8 weeks without exacerbation).
• Cummulative smoking ≥ 10 pack-years.
• Absence of asthma or other chronic respiratory disease that justify the ventilatory disorder (although a history of asthma is not an exclusion criteria);
• Absence of malignancy or very serious comorbidities that would prevent study completion.

Exclusion Criteria:

• Patients <35 years.
• Recent exacerbation (<8 weeks).
• Not giving written informed consent.
• Presence of asthma or other chronic respiratory disease justifying the ventilatory disorder,
• Diffuse bronchiectasis not associated with COPD.
• Presence of malignancy or very serious comorbidities that would prevent study completion.
• Difficulty to perform appropriate follow-up.

Participants will be selected from the outpatient clinics, pulmonary function labs, and / or pulmonology wards of each participating center