The bronchial provocation test is used to determine the degree of bronchial stenosis by using a stimulus to contract the bronchial smooth muscle, and then using lung function as an indicator, thereby determining the degree of airway hyperresponsiveness. According to the different stimulating agents, the commonly used ones can be divided into drug test, exercise test, distilled water or hypertonic saline stimulation test, specific bronchial stimulation test, etc. The characteristics of different bronchial excitation tests: 1. The most commonly used drug test is histamine or acetylcholine The mechanism of action of the two is not exactly the same. The former is a biologically active medium, which can directly stimulate bronchial smooth muscle contraction after inhalation, and also stimulate the vagus nerve endings to reflexively cause smooth muscle contraction; the latter is a cholinergic drug, which directly binds to the acetylcholine receptors on smooth muscle and causes smooth muscle contraction after inhalation. 2.Exercise test Most asthma patients, after strenuous exercise, will induce asthma or make asthma aggravated. It is generally believed that hyperventilation during exercise causes a decrease in the temperature of the airway lining fluid layer and water loss as its main trigger. It is believed that dehydration increases the local osmotic pressure, loosens and separates the tight junctions of epithelial cells, and releases inflammatory mediators from mast cells and eosinophils leading to bronchial mucosal congestion and edema, increased secretions and smooth muscle spasm. 3.Distilled water or hypertonic saline excitation test No response to inhalation of saline in asthmatic patients, while inhalation of hypertonic saline (3.6 ) or hypotonic distilled water can cause bronchoconstriction, and the response mechanism may be that the osmotic pressure of the bronchial mucosal surface fluid is altered. This alteration of the internal environment is a strong stimulus that can degranulate mast cells, release mediators, and stimulate smooth muscle receptors, causing smooth muscle contraction. 4.Specific and occupational bronchial excitation test About 50%-70% of asthma patients are exogenous and allergic to certain allergens. The common ones are pollen, mold, house dust, insects and substances that cause occupational asthma (asthma due to repeated exposure to a high concentration of a substance in the workplace, resulting in increased bronchial reactivity), such as animal fur, bacteria, wood, cotton, cereals, formaldehyde, and illuminated products, etc. Therefore, in order to determine what allergens can cause asthma, the inhalation test of such allergens should be done directly. Evaluation index of bronchial excitation test After the bronchial tubes are stimulated by drugs, the smooth muscle spasms and the bronchial caliber becomes narrower. Since it is difficult to measure the bronchial caliber directly, the change in bronchial caliber is usually indirectly reflected by the change in certain pulmonary function indexes before and after stimulation. The most commonly used pulmonary function indicators are: maximum expiratory flow, total pulmonary resistance and specific airway conductivity. A 20% decrease in FEV1 or an increase in R value to twice the initial resistance is usually used as the threshold. Clinical application of bronchial excitation test: 1. To assist in the diagnosis of asthma AHR is one of the most typical pathophysiological features of asthma, and some patients have chronic cough as the only symptom of asthma. Such patients may develop typical asthma symptoms after several months or years of follow-up. Bronchial hyperresponsiveness is often parallel to the severity of asthma. A mild hyperresponsiveness indicates that medication can be reduced, while a severe one indicates aggressive treatment. It is important to measure the bronchial reactivity as a follow-up tool because it means that the asthma is under control after long-term treatment. The change of bronchial reactivity is often used as an indicator to judge the efficacy of drugs. 3.Research on the pathogenesis of asthma and other diseases Bronchial hyperresponsiveness is a characteristic of asthma, and if the causes of hyperresponsiveness can be elucidated, the pathogenesis of asthma can also be elucidated.