In this study the possible changes in airway geometry and function induced by 6 month oral treatment with Daxas® (roflumilast) will be evaluated. The use of functional respiratory imaging (FRI) on the phenotyping of chronic obstructive pulmonary disease (COPD) patients will be examined. The study population consists of 40 severe COPD patients, global initiative for chronic obstructive lung disease (GOLD) stages III until IV.

Imaging parameters will be assessed and the correlation with lung function and health related quality of life will be checked before and after treatment.

Inclusion Criteria:

• Male or female patient ≥ 30 years old
• Patient with BMI ≥ 20
• Written informed consent obtained
• Female patient of childbearing potential who confirm that a contraception method was used at least 14 days before visit 1 and will continue to use a contraception method during the study.
• Patient should be treated according to GOLD guidelines
• COPD patient with GOLD stages III until IV
• Patient with smoking history of at least 10 pack-years
• Patient takes Spiriva® and a fixed combination of inhaled steroids and long acting beta agonist (LABA) at least 6 weeks before visit 1
• Patient must be able to understand and complete the protocol requirements, instructions, questionnaires and protocol-stated restrictions.

Exclusion Criteria:

• Pregnant or lactating females
• Patient with severe immunological diseases and/ or severe acute infectious diseases.
• Patient with heart failure
• Patient with diagnosis of cancer (except basal cell carcinoma)
• Patient with a history of depression associated with suicidal ideation or behaviour
• Patient with moderate or severe hepatic impairment.
• Patient with lactose intolerance
• Patient is unlikely to comply with the protocol or unable to understand the nature, scope and possible consequences of the study.
• Patient who received any investigational new drug within the last 4 weeks prior to the screening visit or twice the duration of the biological effect of any drug (whichever is longer).