Pulmonary rales are most commonly caused by inflammatory reactions in the lungs, mainly when the organism is invaded by pathogens such as viruses, bacteria, mycoplasma, chlamydia, rickettsia, etc., and inflammatory reactions such as congestion, edema, and exudation of large amounts of inflammatory substances from the lung mucosa occur. At this time, air is inhaled and exhaled through respiratory movements of the lungs, and inflammatory secretions on the mucous membranes of the alveoli and bronchial walls are vibrated, resulting in a sound similar to boiling water, also known as a blistering sound. Depending on the inflammation of the bronchi in the lungs, lung rales can be divided into small, medium and large alveolar sounds. Lung infections, also known as pneumonia, fixed in the lungs can be heard as fixed medium and small blister sounds; bronchiectasis can be heard as mobile large blister sounds in the lungs; some healthy elderly people can also hear fixed rales in the lungs, which are physiological in nature.