Pulmonary function tests are commonly used to diagnose chronic obstructive pulmonary disease, bronchial asthma, chronic bronchitis, etc. 1.Chronic obstructive pulmonary disease (COPD) Pulmonary function test is the main objective indicator to determine chronic obstructive pulmonary disease. After using bronchodilators, FEV1/FVC <70%; total lung volume (TLC), functional residual air volume (FRC), and residual air volume (RV) increase, while spirometry (VC) decreases. Chronic obstructive pulmonary disease (COPD) cannot be cured at present. After diagnosis, patients can only be soothed by improving their living environment (such as quitting smoking, avoiding exposure to airborne irritants, etc.) and medications. 2.Bronchial asthma During an asthma attack, lung volume (VC) is normal or reduced, FEV1, FEV1/FVC% and PEF are decreased, and residual air volume, residual air volume and total lung volume ratio are increased. The presence of airflow limitation can be determined if FEV1/FVC% is <70% or if FEV1 is less than 80% of the normal expected value. Pulmonary function is usually not significantly abnormal in asthma remission, but it can be somewhat reduced in patients with recurrent asthma attacks. In asthma remission, a bronchial excitation test may be performed with a positive result in those with normal pulmonary ventilation function, and a bronchodilator test may be performed with a positive result or a diurnal PET variability of >20% in patients with decreased pulmonary ventilation function. Long-term drug use is required to control symptoms after diagnosis. 3. Chronic bronchiectasis As the disease progresses, the patient’s maximum expiratory flow-volume curve is at 75% and 50%, with a significant decrease in flow rate at lung volume. The disease is also incurable and can only be relieved by medication after diagnosis.