If the patient has black and blue lips: 1. Consider that the patient has various causes of poisoning, such as food poisoning or chemical poisoning, drug poisoning will have this symptom. For example, if a patient has nitrite poisoning, the typical symptoms of blackened lips and cyanosis will occur. 2. If a patient has insufficient blood supply to the heart, often in the presence of chronic coronary heart disease, myocarditis, pericarditis, heart valve disease, rheumatic heart disease, hypertensive heart disease and congenital heart disease, the symptoms will also occur when there is insufficient blood and oxygen supply to the heart muscle cells, coronary artery ischemia and lack of oxygen. 3. Respiratory system diseases, often these symptoms appear when chronic obstructive pulmonary emphysema, chronic pulmonary heart disease, pulmonary hypertension.