The most important factors affecting respiratory airway resistance in clinical practice are the flow of air in the circulating airway, the size of the airway lumen, and the contraction and diastolic forces of the respiratory muscles. Intra-airway resistance is mainly the obstructive force generated by the airway during the respiratory movement of the gas, and under normal conditions, the airway resistance is 1-3 cmH2O/L/S. Airway resistance increases in pathological conditions, such as chronic obstructive emphysema, chronic bronchitis, acute bronchitis, bronchial asthma, bronchopulmonary cancer, diffuse interstitial fibrosis, pneumoconiosis, silicosis, and a variety of trauma-induced Pneumothorax, etc.