The range of movement of the lower lung borders in normal subjects is 6-8 cm, which is equivalent to the range of movement of the diaphragm during respiration and is mainly determined by percussion. The range of movement of the inferior pulmonary border varies from site to site, with the greatest movement occurring in the mid-axillary and post-axillary lines. The decreased mobility of the lower lung border is mainly due to the loss of elasticity of lung tissue, such as chronic obstructive pulmonary disease; there is also atrophy of lung tissue, such as pulmonary atelectasis and pulmonary fibrosis; it can also be seen in inflammation of lung tissue and pulmonary edema. When there is a large amount of fluid in the chest cavity, or pneumothorax or extensive pleural adhesions, the lower lung border and its mobility cannot be tapped out, and the mobility of the lower lung border is lost in patients with phrenic nerve palsy.