Assessment of bronchial hyper reactivity i.e. the ease and intensity with which the bronchi narrow in response to the exposure of various stimuli, such as allergens, cold, exercise, viruses, drugs.
Bronchial hyper reactivity is assessed in the laboratory by the degree of narrowing of the airways by discounting the value of FEV1 after inhalation of a bronchosyspastic agent.
During this examination, the patient performs repeated spirometry before and after inhalation of increasing concentrations of a metacholine, a substance that causes bronchospasm. In patients with bronchial hyper reactivity, inhalation of metacholine may cause a drop in respiratory function, detected by spirometry. This test helps in the diagnosis of asthma, especially in patients who have a non typical history, a non-diagnostic reversibility test with bronchodilator or have a clinical manifestation of cough only.