The amount of diffusion depends on the difference in partial pressure of gas between the two sides of the membrane, diffusion area, distance, time, molecular weight of the gas and its solubility in the diffusion medium. Decreased diffusion function can be caused by emphysema and other lung tissue lesions, diffuse interstitial lung fibrosis, and other diseases. When pulmonary pathology produces diffusion dysfunction clinically, it is often accompanied by a significant ventilation/blood flow dysfunction, the consequences of which all lead to hypoxia. Decreased gas diffusion function: Diffusion function is a measure of ventilation function. It is used to evaluate the efficiency of gas exchange by the alveolar capillary membrane. The diagnosis can be made by clinical examination of spirometry. It is (28.84±4.84) ml/(mmHg-min) in men and (22.13±3.09) ml/(mmHg-min) in women. Below this value there is a decrease in gas diffusion function. Hyperinflation of the lungs: this is commonly referred to as emphysema. Emphysema is a pathological condition in which the airways at the distal end of the terminal fine bronchi (respiratory fine bronchi, alveolar ducts, alveolar sacs and alveoli) are hypoelastic, hyperinflated, inflated and have increased lung volume or are accompanied by destruction of the airway walls. There are several types of emphysema according to their pathogenesis: senile emphysema, compensatory emphysema, interstitial emphysema, focal emphysema, paracentral emphysema, and obstructive emphysema. Hyperventilation syndrome: It is a disease of the body and mind. Due to the patient’s excessive fatigue and mental stress, it stimulates the excitation of the vegetative nerves and causes an accelerated respiratory rate. This makes the inhaled oxygen and exhaled carbon dioxide increase, but the blood is saturated with oxygen, so the excess oxygen is not exchanged into the blood, which is equivalent to excessive CO2 emission. And CO2 is the raw material of H2CO3 in blood, so the decrease of blood H2CO3 disrupts the blood acid-base balance and triggers respiratory alkalosis. If it does not improve, it may cause organ failure.