Cough and sputum in COPD are primarily due to changes in

Large airways- Cigarette smoking often results in mucus gland enlargement and goblet cell hyperplasia, leading to cough and mucus production that define chronic bronchitis, but these abnormalities are not related to airflow limitation.Small airways- The major site of increased resistance in most individuals with COPD is in airways <=2 mm diameter.Lung parenchyma- Emphysema is characterized by destruction of gas-exchanging air spaces, i.e., the respiratory bronchioles, alveolar ducts, and alveoli.Ref: Harrison 19e pg: 1701