Modification of Chronic Inflammation by Inhaled Carbon Monoxide in Patients With Stable Chronic Obstructive Pulmonary Disease (COPD)

Inclusion Criteria: * Men and women, age \> 40 years. Women must be post-menopausal (i.e. at least one year must have passed after the last menstruation), surgically sterile or using acceptable contraceptives, as judged by the investigator. * A diagnosis of COPD according to the criteria of the American Thoracic Society (ATS); a disease state characterised by the presence of chronic airway obstruction due to chronic bronchitis (cough/sputum on most days a week for 3 months a year for at least two successive years); or emphysema. * FEV1 \> 0.7 litres * FEV1/FVC ratio \< 70% (equation retrieval system \[ERS\] equations) * A smoking history of \> 10 pack years * Completely stopped smoking \> 1 year ago * No upper or lower respiratory tract infection in the last 4 weeks * In a stable phase of COPD, as judged by the investigator * Signed and dated informed consent obtained before any study related procedures (including withdrawal of concomitant medication) are conducted Exclusion Criteria: * Treatment with immune-modulating agents for any other disease * History of asthma; former diagnosis of asthma * Arterial oxygen tension (PaO2) \< 8.0 kPa * Any significant other pulmonary disease or disorder (e.g. alpha1-antitrypsin deficiency, bronchiectasies), as judged by the investigator * Patients with other significant disease or disorder (like cardiovascular, gastrointestinal, liver, renal, neurological, musculoskeletal, endocrine, metabolic \[including diagnosed diabetes\], malignant, psychiatric, major physical impairment), which, in the opinion of the investigator may either put the patient at risk because of participation in the study; or may influence the results of the study, or the patient's ability to participate in the study. * Patients unable to blow reproducable lung function measurements * Patients using medicine with anti-oxidant character like n-acetyl-cysteine.