Bronchodilation is the effect of dilation or dilatation of the bronchi, that is, the bronchi are widened, leading to a better passage of the air through the airways.
Asthma and chronic obstructive pulmonary disease (COPD) are characterised by bronchoconstriction, the narrowing of the airways, leading to difficult breathing. This may be intermittent, with periods of narrowing alternating with periods is which the bronchi are dilated. In some patients the narrowing may become irreversible.
The bronchodilator test is used to assess the reversibility of bronchoconstriction. First a study of lung function is performed, then the patient receives a bronchodilating drug, and the study is repeated 15-30 minutes later. The results are compared to check if there is an improvement in lung function and, if so, the test is considered to be positive.
The test is used to support a diagnosis of asthma or COPD, to assess severity, to monitor the disease, to check the effect of another treatment. The test can be negative in some patients with asthma if they are in a period free of symptoms, or, on the other side, if they have irreversible changes in the airways. The medications used for asthma may also affect the results, so the doctor will consider several variables for interpreting the test.
If you are scheduled for a bronchodilator test you should ask your doctor if you must withdraw the medication. The doctor might want to know the result of the test with no modification by the medication, but might also want to know if the medication is protecting you.