COPD comprises major pathological changes in the following four different compartments of the lung, which are variably present in individuals with the disease: central airways, peripheral airways, lung parenchyma and pulmonary vasculature.

• Central airways (cartilaginous airways >2mm of internal diameter)
• Peripheral airways (noncartilaginous airways <2mm internal diameter)
• Lung parenchyma (respiratory bronchioles, alveoli and capillaries)
• Pulmonary vasculature