Rales are additional to breath sounds due to tracheobronchial or luminal obstruction and other pathologies; depending on the nature of the sound, they can be divided into dry rales and wet rales, which are generally categorized as snoring and whistling sounds; wet rales have a thick, medium, and thin sound, and twisting and fine wet rales are very similar in nature and sometimes difficult to differentiate. Dry rales can be diagnosed by clinical manifestations and some instrumental examinations: 1. They are high pitched, musical, and long lasting, and can be heard in both inhalation and exhalation, but are evident in exhalation, with a high degree of emphasis, changeable nature and location of the rales, and the number of rales can be significantly increased or decreased in an instant. 2. Dry rales occurring in the airway can sometimes be heard without a stethoscope and are called stridor. Classification of dry rales (1) High-pitched dry rales: Also known as whistling rales, they are high pitched, with a base frequency of >500 Hz, a short “Zhi-Zhi” sound or a musical sound, and an ascending tone during expiration; they occur in the smaller bronchi or fine bronchi. Whistling sounds are high-pitched dry rhonchi that are often described as croup, fricatives, and birdsong, and occur in the bronchi and bronchi. (2) Low-pitched dry rales: also known as snoring, are low-pitched, have a gene frequency of <200 Hz, and are characterized as moaning or snoring sounds, most often occurring in the trachea or main bronchi. If the dry rales in the lungs, in the expiratory phase is mainly dry, and with obvious prolongation of expiration, generally called croup. Snoring, the lesion occurs in the trachea or main bronchus; if the snoring is caused by mucus retention, it disappears after coughing; localized fixed snoring is suggestive of bronchial obstruction, and if snoring occurs repeatedly in the same area, it is necessary to consider bronchial stenosis caused by mucus retention; snoring caused by bronchial spasm is bilaterally long. Distribution site Bilateral diffuse dry rales, seen in bronchial asthma, slow bronchial wheezing type and cardiogenic asthma limited dry rales, seen in endobronchial tuberculosis, tumors, which are caused by local bronchial stenosis.