Catarrhal sounds can occur after injury or after the clot has dissolved outside the arteriovenous communication. In most patients, arterial pulsations can still be felt in the limb distal to the arteriovenous fistula, but they are weaker than on the healthy side. In patients with catatonia, the superficial femoral artery of the lower extremity with injury to the deep femoral artery cannot be palpated in the dorsalis pedis artery, and there are signs of limb ischemia. Therefore, clinically cat stridor needs to be diagnostically differentiated from the following symptoms (1) Mechanism: Reduced air flow into the alveoli, slowed flow rate and impaired sound conduction. (2) Etiology: restricted thoracic activity, such as chest pain, rib resection, pleural hypertrophy, etc.; respiratory muscle diseases, such as myasthenia gravis, diaphragmatic paralysis, etc.; airway obstruction, such as chronic bronchitis, bronchial asthma; compressive atelectasis, commonly seen in pleural effusion, pneumothorax, abdominal diseases, such as large amounts of ascites, abdominal giant tumors, etc. (2) Increased alveolar breath sounds: (1) Mechanism of occurrence: Increased air flow into the alveoli and accelerated flow rate. (2) Causes: Increased oxygen demand of the body, such as fever, hypermetabolism, exercise, etc.; hypoxia excites the respiratory center, such as anemia; blood acidity increases, stimulating the respiratory center, breathing becomes deeper and longer, such as acidosis. All of the above are bilateral, and in one side of thoracic lung disease, compensatory alveolar respiratory sound enhancement may occur in the healthy lung.