The cough is a protective physiological reflex produced by the stimulation of the respiratory tract mucosa. It is manifested as a strong expiratory action in which the vocal cords are tightly closed after a short deep inspiration and the expiratory muscles suddenly and strongly contract, resulting in a sharp rise in lung and intrathoracic pressure within a short period of time, forcing the vocal cords to open suddenly and then the gas in the lungs rushes out of the vocal cords at a very high speed, which produces the sound called cough. Coughing rarely occurs in normal people and in most cases is pathological. Factors that cause coughing 1. Physical factors. Mechanical obstruction, compression or distortion of the lumen causing irritation of the canal wall causes coughing. For example, inhalation of vomit or other foreign bodies into the respiratory tract; caused by mediastinal tumors, esophageal lesions, lung tumors, pneumothorax, etc. 2.Chemical factors. Various irritating gases, such as smoking, inhalation of cold air, industrial waste gas, etc. This can cause congestion and inflammation of the respiratory tract and lungs, thus causing coughing. 3. Infection factors. Infection is a common cause of coughing, with local inflammatory irritation causing coughing. 4. Allergic factors. Allergens can cause cough and asthma, such as pollen and dust. Common diseases that cause cough 1. Respiratory diseases: They are the most common causes of cough. Diseases of the throat such as pharyngitis, laryngitis and laryngeal cancer; lung diseases such as chronic bronchitis, bronchial asthma, acute pneumonia, tuberculosis, lung abscess, bronchiectasis, lung cancer and tracheal tumors; pleural diseases such as pleurisy and pneumothorax, etc. 2. Cardiovascular diseases: Left heart failure due to various causes can cause an increase in left atrial pressure, resulting in pulmonary stasis leading to coughing, such as mitral stenosis, mitral valve insufficiency, aortic stenosis and/or insufficiency; in pulmonary embolism, the exudate stimulates the alveolar wall and bronchial mucosa and also causes coughing. 3. Digestive system diseases: The mechanism of gastroesophageal reflux is that the distal mucosa of the esophagus is exposed to acidic gastric juice and then stimulates the vagus nerve to cause an esophageal-bronchial cough reflex; in addition, when a small amount of esophageal contents is accidentally aspirated into the tracheobronchus or pharynx, the mucosa is stimulated to cause a cough reflex; this is commonly seen in reflux esophagitis, etc. 4. Central nervous system diseases: the cough reflex center is located in the medullary cough center, and people can induce coughing or inhibit the cough reflex at will: central system diseases that cause coughing include: encephalitis, cerebral hemorrhage craniocerebral trauma, brain tumors, etc. Characteristics of cough 1. Nature of cough. Attention should be paid to whether the cough is accompanied by coughing sputum, the nature of the sputum and the amount of sputum. Dry cough: refers to cough with no sputum or very little sputum, which can be seen in acute pleurisy, diaphoretic stenosis, etc.; irritating dry cough is no sputum, which is common in pleurisy, lung cancer, etc. Wet cough: refers to cough with sputum, which can be seen in bronchiectasis, lung abscess, etc. 2. Time and rhythm of cough. Attention should be paid to the time of appearance of cough symptoms, whether they are persistent or paroxysmal, and whether there is any regularity. For example, persistent cough is most often seen in lung cancer; chronic cough is most often seen in chronic bronchitis, bronchiectasis, chronic fibro-cavitary tuberculosis, etc. 3, age and gender. Choking cough in children can be caused by foreign body aspiration, bronchial lymph node enlargement compressing the trachea and bronchi; recurrent cough with or without cyanosis in children should be considered as possible asthma and congenital heart disease. Patients above middle age, especially men who are frequent smokers, should be aware of lung cancer. 4. Cough tone. The cough with an irritating metallic tone can be caused by direct compression of the trachea by mediastinal tumors, aortic aneurysms or bronchial cancer; hoarse cough is seen in vocal fold paralysis caused by vocal fold inflammation, vocal fold tumors, laryngeal cancer or compression of the recurrent laryngeal nerve. 5. Accompanying symptoms of cough. Most of them have important differential diagnostic value. Cough with fever should be considered as pneumonia, lung abscess and pleurisy; cough with chest pain is seen in pleurisy and lung cancer; cough with hemoptysis is seen in tuberculosis, bronchiectasis and lung cancer; cough with croup is seen in bronchial asthma and cardiogenic asthma, etc. Characteristics of cough in lung cancer Although cough is a symptom that occurs in many respiratory diseases, cough in lung cancer has some characteristics of its own. Early stage of lung cancer often presents with irritating dry cough, which can be easily mistaken for respiratory tract infection. Central type lung cancer endobronchial mass causes bronchial narrowing, and the cough is persistent with a high-pitched metallic sound; when secondary lung infection occurs, the sputum volume increases significantly and is mucus or pus in nature. Cough with blood in sputum Cancer tissue is rich in blood vessels, and blood in sputum may appear after rupture, or intermittent bloody sputum; hemoptysis is rare.