Bronchoalveolar breath sounds can be heard in the region of normal alveolar breath sounds. When lower airway resistance increases, inspiration and expiration are both difficult. Since the alveoli in the inspiratory phase are dilated and the airway diameter is relatively large, the airway resistance in the inspiratory phase is smaller than that in the expiratory phase, so the increased airway resistance is mainly manifested by prolonged expiration time. The strength of alveolar breath sounds in normal subjects is related to the depth of breathing, the size of the elasticity of the lung tissue, the thickness of the chest wall, and the age and gender of the subject. How many aspects are there in the diagnosis of prolonged expiratory sounds? Diminished or absent alveolar breath sounds: 1. Affect the conduction of alveolar breath sounds Unilateral diminished alveolar breath sounds can be seen in pneumothorax, pleural effusion and pleural hypertrophy. In bilateral cases, it can be seen in bilateral pneumothorax, bilateral pleural effusion and bilateral pleural hypertrophy. Restricted alveolar breath sounds are diminished in restricted pneumothorax, encapsulated pleural effusion and restricted pleural hypertrophy. 2, affecting the expansion of the thorax or lung Unilateral diminished alveolar breath sounds can be seen in total pulmonary atelectasis, tracheal intubation deep into one side of the main bronchus, and rib fracture. Bilateral ones can be seen in late pregnancy, massive ascites and huge tumors in the abdominal cavity. Restricted cases can be seen in lobar atelectasis. 3. Insufficient ventilatory power Unilateral diminished alveolar breath sounds can be seen in diaphragmatic paralysis, and in bilateral cases in central respiratory depression, anesthetic or sedative overdose, hypokalemia, respiratory muscle weakness or fatigue. 4.Increased ventilatory resistance Unilateral diminished alveolar breath sounds can be seen in central lung cancer and lymphoma. Bilateral ones can be seen in chronic bronchitis, asthma, and obstructive emphysema. Restricted cases can be seen in bronchial tuberculosis, bronchial foreign bodies and tumors. Enhanced alveolar breath sounds: 1. Physiological enhanced alveolar breath sounds: seen in infants and children or adults with thin chest walls and physical activity. 2, pathological alveolar breath sounds: seen in fever, hypermetabolism, anemia and acidosis, etc. Enhanced alveolar breath sounds are usually bilateral, but when one side of the lung or pleura is diseased, compensatory enhanced alveolar breath sounds can occur on its opposite side, such as tuberculosis, pneumonia, lung tumor, pneumothorax, pleural fluid and pleural hypertrophy.