The main way to test lung function is through a pulmonary function test. There is no need to hold your breath during the lung function test, just cooperate with the doctor to perfect your breathing maneuvers. Lung function tests reflect the function of the lungs by measuring lung volume, ventilation, air exchange, and small airway function. Lung function tests are useful in the diagnosis of respiratory diseases such as bronchial asthma, chronic obstructive pulmonary disease, restrictive and interstitial diseases. Lung function test process needs to cooperate with the doctor to complete a series of breathing movements, such as inhaling with maximum force, holding the breath, and exhaling with maximum force and speed until complete exhalation and other actions. Lung function tests are non-invasive and less harmful, but they are not suitable for everyone. Lung function tests are not suitable for patients who have recently suffered from serious arrhythmia, heart failure, severe hyperthyroidism, or poorly controlled severe high blood pressure.