Coughing up foamy mucus sputum is one of the symptoms of chronic bronchitis, which is a chronic non-specific inflammation of the tracheobronchial mucosa and its surrounding tissues caused by infectious or non-infectious factors. Its pathology is characterized by hyperplasia of bronchial mucus glands and increased mucus secretion. Infection is one of the most important factors in the development of chronic bronchitis. Viral mycoplasma and bacterial infections are the main causes of acute attacks of the disease. Viral infections are common with influenza virus rhinovirus adenovirus and respiratory syncytial virus, bacterial infections are common with Streptococcus pneumoniae Haemophilus influenzae Catarrhella and Staphylococcus, bacterial infections occur every time secondary to viral or mycoplasma infections on the basis of damaged airway mucosa. . Ancillary examinations for coughing up foamy mucus sputum: 1. Sputum examination: The appearance of sputum during acute attacks is mostly purulent. A large number of neutrophils can be seen on smear examination, and more eosinophils can be seen in combined asthma. Sputum culture can be seen in the growth of Streptococcus pneumoniae, Haemophilus influenzae and Catarrhella. 2. Leukocyte classification count: Total leukocyte count and differential count are mostly normal in patients in remission. The total leukocyte count and neutrophil count may be increased in acute exacerbation with bacterial infection. Blood eosinophils may be increased in patients with combined asthma. 3. X-ray examination: There may be no obvious changes in the early stage. Auxiliary examinations of chronic bronchitis can reveal thickened and disorganized texture of both lungs in repeated acute attacks, with reticular or striated and speckled shadows, which are obvious in the lower lung fields. This is due to thickening of the bronchial tube wall, infiltration or fibrosis of inflammatory cells in the fine bronchial or alveolar interstitium. 4, pulmonary function tests: one second forceful expiratory volume and one second forceful expiratory volume/forceful spirometry ratio in the early stage mostly no significant changes. When there is airflow obstruction, the ratio of first second expiratory volume (FEV 1) and FEV 1 to lung volume (VC) or forceful lung volume (FVC) is reduced (<70%). When small airway obstruction is present, the maximum expiratory flow-volume curve can be significantly lower at 75% and 50% of lung volume. This is one of the ancillary tests for chronic bronchitis.