Compensatory emphysema is a normal physiological process, because the total area of the lung decreases after partial lung resection, and in order to ensure the body’s oxygen needs, the other side of the lung becomes compensated for the expansion, thus forming compensatory emphysema. Generally, compensated emphysema is asymptomatic. However, if the lung loses this function, it is non-compensated emphysema. What are the causes of compensated emphysema? It is mostly seen in diseases such as pneumonia, atelectasis, abscess chest, and pneumothorax. Due to the damage of the diseased lung tissue, the volume is reduced, so the healthy lung expands and fills the empty space, thus forming compensatory emphysema. In this type of emphysema, there is no bronchial obstruction due to simple alveolar expansion, and the emphysema disappears when the original disease is cleared. 1. Pneumonia Pneumonia refers to inflammation of the terminal airways, alveoli and interstitial lung, and can be caused by disease microorganisms, physicochemical factors, immune damage, allergies and drugs. Bacterial pneumonia is the most common form of pneumonia and one of the most common infectious diseases. Pneumonia as it is commonly referred to is mainly caused by bacterial infections, and this pneumonia is also the most common one. Before the application of antibiotics, bacterial pneumonia was a great threat to the health of children and the elderly, and the advent and development of antibiotics once led to a significant decrease in the death rate from pneumonia. However, in recent years, despite the use of powerful antibiotics and effective vaccines, the overall death rate from pneumonia has not decreased and has even increased. 2. Pulmonary atelectasis Pulmonary atelectasis refers to a decrease in the volume or air content of one or more lung segments or lobes. As a result of intra-alveolar gas absorption, atelectasis is usually accompanied by a decrease in the translucency of the affected area, aggregation of adjacent structures (bronchi, pulmonary vessels, interstitial lung) into the atelectasis area, sometimes solid alveolar cavities, and compensatory emphysema of other lung tissues. Collateral gas traffic between lung lobules and segments (and occasionally lobes) may allow a degree of light transmission to remain in areas of complete obstruction. Pulmonary atelectasis can be classified as either congenital or acquired. Congenital pulmonary atelectasis is a condition in which the infant is born without gas filling the alveoli, with severe clinical dyspnea and cyanosis, and in which the child dies of severe hypoxia after birth. The vast majority of pulmonary atelectasis is clinically acquired and is the focus of discussion in this chapter. Pleural cavity is infected by purulent pathogens and produces purulent exudate accumulation, which is called abscess thorax. According to the scope of lesion, it is divided into total pustulothorax and limited pustulothorax. Full pus chest means that the pus occupies the whole pleural cavity, and limited pus chest means that the pus accumulates between the lung and the chest wall or the transverse septum or the mediastinum, or between the lung lobes and the lung lobes, also called wrapped pus chest. 4, pneumothorax Pneumothorax is the pathophysiological condition caused by the rupture of the dirty pleura without trauma or human factors, and the gas enters the pleural cavity resulting in the accumulation of air in the pleural cavity. Pneumothorax is called idiopathic pneumothorax when it is formed by rupture of subpleural emphysema bubbles without obvious lung lesions; secondary pneumothorax is called secondary pneumothorax when it is secondary to pleural and lung diseases such as chronic obstructive pulmonary tuberculosis. According to the pathophysiological changes, it is further divided into three categories: closed (simple), open (traffic) and tension (high pressure).