A 69-year-old man with a 50 pack-year smoking history presents with a chronic productive cough for the last 5 years, present most days for at least 3 months each year. He also reports increasing breathlessness on exertion and occasional wheeze. Post-bronchodilator spirometry results are: FEV1 1.4 L (52% predicted), FVC 2.5 L (70% predicted), FEV1/FVC ratio 0.56. What is the most likely diagnosis based on the clinical history and spirometry results?