Patients are short of breath and cannot catch air, which is a manifestation of dyspnea and can be seen in many causes, including respiratory system diseases, cardiovascular system diseases, etc., as follows: I. Respiratory system diseases: This symptom is more common in respiratory system diseases, such as the rupture of the pleural cavity caused by trauma, which leads to a large amount of gas entering the pleural cavity and compressing the normal lung tissue, thus leading to pneumothorax. Diffuse inflammation of the lungs due to infection by septic bacteria, Mycobacterium tuberculosis, fungi, parasites, and other pathogens. The lung mucosa becomes congested, edematous, and inflammatory secretions exude, which can also be seen in acute attacks of chronic obstructive pulmonary emphysema and chronic pulmonary heart disease. In addition, it can be seen in patients due to the stimulation of allergens, resulting in airway hyperreactivity, so that acute attacks of bronchial asthma. Cardiovascular system diseases: This symptom can be seen in cardiovascular system diseases, due to congenital heart disease, heart valve disease, resulting in left heart failure and pulmonary edema.