Breathing out tight dyspnea may be caused by respiratory system diseases, cardiovascular diseases, etc. It can also be seen in obesity, allergy and other conditions. 1. Respiratory diseases: when the patient exists airway obstruction, pleural disease, mediastinal disease and other causes of respiratory effort, resulting in dyspnea, and in severe cases, causing flaring of the nose, and even cyanosis. 2. Cardiovascular diseases: cardiac tamponade, heart failure, etc. cause insufficient circulatory perfusion, which results in dysfunction of the body’s gas exchange, causing dyspnea. In addition, obesity, allergies or strenuous exercise can also cause tightness of breath, dyspnea and other symptoms, if the situation is serious impact on normal life, should consult a doctor in a timely manner to clarify the diagnosis, so as to take targeted treatment.