Note the identification of different diseases that cause a decrease in diffusion function. Diseases such as emphysema and other lung tissue lesions, diffuse interstitial lung fibrosis, etc. There is often a significant ventilation/blood flow imbalance (effective ventilation depends not only on the area and thickness of the alveolar membrane, total alveolar ventilation and blood flow, but also on the coordination of alveolar ventilation and blood flow. In pulmonary disease, total lung ventilation and blood flow can sometimes be normal, but uneven distribution of ventilation and blood flow and severe disproportion (ventilation-perfusionmbalance) can prevent effective ventilation. (This is the most common mechanism of respiratory failure due to lung disease), the consequences of which all lead to hypoxia. Emphysema and other lung tissue lesions, diffuse interstitial lung fibrosis and other diseases interstitial lung disease, chronic obstructive pulmonary disease, alveolar lesions such as lung infections, pulmonary edema, alveolar hemorrhage, alveolar protein deposition, thoracic and pleural lesions, cardiovascular disease, patients with anemia or erythrocytosis, patients with recurrent upper respiratory tract infections, patients with a history of smoking and chronic cough, patients with seasonal coughing episodes.