Lung function tests usually include five items: tidal volume (VT), deep inspiration (IC), lung capacity (VC), total lung capacity (TLC), and forceful lung capacity (FVC). 1. Tidal volume (VT): Tidal volume is the flow of air into the lungs during a single quiet breath. The tidal volume of an adult is about 500ml, which can check whether the respiratory muscle function is abnormal. 2. Deep Inspiratory Capacity (IC): Deep Inspiratory Capacity (DIC) is the volume of gas that can be inhaled during a maximal inspiration at the end of a calm expiration. The reference value is 2069~3165ml for men and 1589~2351ml for women, which can determine the condition of inspiratory muscle strength. 3. Vital Capacity (VC): Vital Capacity is the maximum amount of gas that can be exhaled after maximum inhalation. It can determine whether there is respiratory muscle dysfunction or restrictive ventilation disorder. 4. Total Lung Capacity (TLC): Total Lung Capacity is the amount of all gases contained after a deep inhalation. If the total lung volume increases, it may be obstructive emphysema, and if the total lung volume decreases, it is seen in restrictive lung disease. 5. Forceful Ventilation Capacity (FVC): Forceful Ventilation Capacity (FVC) is the amount of gas that can be exhaled with maximum force and speed after a deep inhalation into the entire lung. It can determine whether the lung ventilation function is normal or not. In addition to the above five tests, there are also related clinical tests such as complementary respiratory volume (ERV), complementary inspiratory volume (IRV) and maximum ventilation volume (MVV).