Computational Fluid Dynamics (CFD) is a new functional imaging method. Since CFD is very sensitive to detect small changes, it might be worthwhile to study the acute effect of formoterol and budesonide combination therapy (Symbicort® forte Turbohaler®) on the upper airway dimensions in severe COPD patients (GOLD III). The increased sensitivity of this technique makes it possible to detect changes in airway caliber in early stages. The regional distribution of resistance and the change in this parameter will provide more insight into the mode of action of the product.

Inclusion Criteria:

1. Patients with documented COPD based on the following criteria:

   Smoking history of at least 10 pack-years and decreased Tiffeneau index (FEV1/(F)VC < 0.70).

2. Patients should present severe COPD with an FEV1 between 50 and 30% of predicted (GOLD 3).

3. Male or female patients aged ≥ 40 years.

4. Patients should be treated according to GOLD guidelines before study start.

5. Patients with, in the opinion of the investigator, a co-operative attitude and ability to be trained to correctly use the TurbohalerR.

6. Maintained on stable respiratory medications for 6 weeks prior to visit 1.

7. Written informed consent obtained.

Exclusion Criteria:

1. Pregnancy, breast-feeding or planned pregnancy during the study. Fertile women not using acceptable contraceptive measures, as judged by the investigator.
2. Inability to carry out pulmonary function testing.
3. A respiratory infection or exacerbation of COPD in the four weeks prior to screening.
4. Any significant disease or disorder which, in the opinion of the investigator, may either put the patient at risk because of participation in the study, or influence the results of the study, or the patient's ability to participate in the study
5. A history of asthma, cystic fibrosis, central bronchiectasis, interstitial lung disease or pulmonary thromboembolic disease.
6. Cancer or any other chronic disease with poor prognosis and/or affecting patient status.
7. A history of thoracotomy with pulmonary resection.
8. Allergy, sensitivity or intolerance to study drugs and/or study drug formulation ingredients.
9. History of alcohol or drug abuse.
10. Patients unlikely to comply with the protocol or unable to understand the nature, scope and possible consequences of the study.
11. Patients who received any investigational new drug within the last 4 weeks prior to the screening visit.
12. Patients treated with any non-permitted concomitant medication (see 7.2).