The main purpose of human respiration is to enable the body to exchange gases with the external environment, including external and internal respiration. External respiration often consists of pulmonary ventilation and pulmonary ventilation, which refers to the passage of gases through the airways into the lung tissue. Pulmonary ventilation refers to the exchange of gases with a high oxygen content entering the lung tissue with gases with a high carbon dioxide content in the alveolar capillaries, facilitating carbon dioxide elimination. Internal respiration usually refers to the exchange of gases between tissue cells and the blood, delivering oxygen from the blood to the cells and expelling carbon dioxide into the blood. Through internal and external respiration, carbon dioxide produced by the body’s tissue cells can be discharged, oxygen can be taken in, and cell metabolism can be promoted. The normal adult respiratory rate is 16-20 breaths/minute when quiet, and the volume of gas inhaled and exhaled each time is about 500mL, which is called the tidal volume. When lung disease occurs, the lung function may decline, and the tidal volume of the lungs will be reduced.