Lung function tests include ventilation, gas exchange and respiratory system resistance, etc. Commonly used indexes include FEV1, FVC, FEV1/FVC, etc. They are mainly used for the examination of lung ventilation function, and can be used to diagnose chronic obstructive pulmonary disease, bronchial asthma and other diseases. 1. FEV1 is the first second expiratory volume, which indicates the amount of gas exhaled in one second of time. 2. FVC is the Forceful Expiratory Volume, which indicates the maximum volume of gas that can be exhaled as fast as possible using maximum force after inhalation. 3. FEV1/FVC is the ratio of the total expiratory volume to the expiratory volume in the first second, which is more than 70% in normal people. If this ratio is less than 70%, it can determine that there is airway obstruction, which is a guide to the diagnosis of chronic obstructive pulmonary disease (COPD). Lung function test can make qualitative and quantitative evaluation of the basic condition of respiratory physiological function of the examinee, and clarify the degree and type of pulmonary dysfunction. Pulmonary function tests are important for studying the pathogenesis and pathophysiology of the disease, clarifying the diagnosis, guiding the treatment, judging the efficacy and evaluating the tolerance of major thoracic and abdominal surgeries, etc., and should be performed under the supervision of a doctor.