The basic cause of bronchiectasis is due to infection of the bronchi and lung tissue, as well as bronchial blockage. Infections can cause blockages, and blockages can also lead to infections. The two influence each other, promoting the occurrence and development of bronchiectasis. This results in damage to the bronchial walls and leads to a large amount of purulent sputum, mainly due to an increase in secretions. Additionally, chronic infection or fibrosis of the lung tissue can also lead to bronchial dilation, causing the bronchial walls to dilate and become congested.