Phase IV O2 Consumption Study in COPD Patients.

Inclusion Criteria:

1. Signing of the informed consent form (ICF) prior to any study specific procedures, including withholding of medications.
2. Male or female, aged 40 to 80 years, inclusive, at Screening (Visit 1).
3. Has a clinical diagnosis of COPD according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2014 guidelines with a post bronchodilator FEV1/FVC <0.7 at Screening (Visit 1).
4. Has a post-bronchodilator FEV1 ≤65% of predicted value at Screening (Visit 1). National Health and Nutrition Examination Survey (NHANES) predicted normal standards will be used for all subjects.
5. Has an increase in IC of >10% after the administration of 1 inhalation of open-label Symbicort pMDI administered with a spacer at Screening (Visit 1).
6. Has a cigarette smoking history of more than 10 pack-years (number of cigarettes smoked per day × number of years smoked)/20).
7. Be able to understand and comply with study requirements, as judged by the Investigator.

Exclusion Criteria:

1. Subject is an employee or relative of an employee involved in the planning and/or conduct of the study (applies to both AstraZeneca staff and/or staff at the study site).
2. Previous enrollment or randomization in this study.
3. Participation in another clinical study with an investigational product (IP) during the last 30 days prior to Screening (Visit 1).
4. Subjects who are unable to discontinue their regular chronic COPD medications (including LAMAs and/or LABA/ICS) and/or who are unable or unwilling to comply with study requirements.
5. Subjects who are taking uLABAs (indacaterol, vilanterol) or uLABA-containing products.
6. Subjects who are taking PDE-4 inhibitors (roflumilast).
7. Subjects who are taking oral corticosteroids on a chronic, regular basis.
8. Subjects using daytime oxygen therapy.
9. Subjects who are currently pregnant (confirmed with positive pregnancy test) or breast feeding.
10. History of respiratory tract infection (including the upper respiratory tract) and/or pulmonary exacerbation within 6 weeks prior to Screening (Visit 1).
11. Pulmonary resection or lung volume reduction surgery within 12 months prior to Screening (Visit 1), or history of lung transplantation, or, in the Investigator's opinion, the subject may need thoracotomy or other lung surgery during the study.
12. History or current diagnosis of asthma and/or alpha 1 anti-trypsin deficiency.
13. Known active tuberculosis.
14. History of interstitial lung or massive pulmonary thromboembolic disease.
15. History of bronchiectasis secondary to respiratory diseases other than COPD (eg, cystic fibrosis, Kartagener's syndrome, etc).
16. Any clinically significant disease or disorder (eg, cardiovascular, gastrointestinal, liver, renal, neurological, musculoskeletal, endocrine, metabolic, psychiatric, major physical impairment) which, in the opinion of the Investigator, may put the subject at risk because of participation in the study, may influence the results of the study, or may affect the subject's ability to participate in the study.
17. Recent (within 12 months prior to Screening [Visit 1]) history of myocardial infarction, recent history of heart failure (New York Heart Association [NYHA] class III and IV, pulmonary edema, and/or cardiac arrhythmia.
18. Previous or current history of lung cancer.
19. History of cancer (within 5 years prior to Visit 1), except for non-metastatic, non melanoma skin cancer.
20. Subjects who cannot perform spirometry manuevers or tolerate body plethysmography.
21. Subjects with known hypersensitivity to Symbicort, its monocomponents (budesonide or formoterol), or its excipients.