The diameter of the subglottis is 5.5 to 6 mm. If the subglottis is obstructed due to abnormal development, it is called congenital subglottic stenosis. It is an acute inflammation of the laryngeal mucosa that leads to vocal fold or excessive fatigue of the vocal folds due to frequent mispronunciation. This disease should be distinguished from acute laryngitis, tracheitis, and bronchitis. 1, acute laryngitis Acute laryngitis is an acute catarrhal inflammation of the laryngeal mucosa, often secondary to acute rhinitis, sinusitis, acute pharyngitis, as part of the entire upper respiratory tract infection, but can also occur alone. Sometimes shouting, excessive use of the voice, and violent coughing can also cause acute laryngitis. If it occurs in children, the condition is more serious. 2. Tracheitis Tracheitis is an inflammatory change in the mucous membrane of the trachea and bronchi caused by infectious or non-infectious factors, with increased secretion of mucus, clinically characterized by prolonged coughing, sputum production or with wheezing. The early symptoms of the disease are mild, mostly occurring in winter and remitting after the spring, and the course of the disease is slow, so it is not noticed. In the late stage, when the disease progresses and is complicated by obstructive emphysema, the lung function is damaged, affecting health and labor force greatly. This disease is one of the common diseases in China, the age of onset is more than 40 years old, smoking patients are significantly higher than non-smoking patients, the prevalence in China is higher in the north than in the south, rural than urban incidence is slightly higher. 3, bronchitis Bronchitis is a chronic non-specific inflammation of the trachea, bronchial mucosa and its surrounding tissues. It is characterized clinically by chronic cough, sputum or with wheezing and recurrent episodes. Chronic cough, coughing or with wheezing, with episodes lasting 3 months per year for 2 years or more, and can exclude other disorders of the heart and lungs and recurrent episodes, some patients can develop into obstructive emphysema, chronic pulmonary heart disease. The disease is appropriate to eat more vitamin B2, B6 can promote the development of the skin is also conducive to the development of the voice. Calcium can promote the development of thyroid cartilage, eating should pay attention to chewing slowly, do not gobble. Particular attention should be paid to eating fish to prevent fish spines from hurting the throat. And should eat some soft food and fine food, should not eat coarse, hard, dry food, etc., to prevent damage to the throat. Do not shout, get tired or sleep too much during the voice change period, and do not cause mood swings to prevent throat congestion and damage to the vocal cords. Reduce or remove secretions from the laryngeal cavity, thus reducing the breeding of bacteria. It helps to prevent the occurrence of pharyngitis.