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When the methacholine is inhaled it produces a narrowing of the airways, which enables to evaluate whether the patient partially loses bronchial calibre. This phenomenon of loss of bronchial calibre, called bronchoconstriction, is evaluated using spirometry.
How is it done?
An initial spirometry is done to know the baseline pulmonary values. The test consists of inhaling a drug (methacholine) at different concentrations. It starts with a low dose of methacholine and a spirometry is performed to check the degree of bronchial obstruction. If the bronchiole is not obstructed significantly (a decrease in the expired volume of less than 20% compared to the initial one), the concentration of the drug is gradually increased until the battery of doses set out in the protocol has finished. If no significant decreases in pulmonary volumes are detected at the end of the test, it is considered to be negative. On the other hand, if the patient has a significant decrease in the expired volume (bronchoconstriction) at any of the doses, the test is concluded and it is considered that the test is positive. Once the test has ended inhaled salbutamol is given to reverse the bronchoconstriction induced by the study.
How should the patient be prepared?
To perform the test, the patient must not be administered treatment with inhalers as it could have an effect on the methacholine.
Who will carry out the test?
The test will be carried out by nursing staff, technicians, or physiotherapist familiarised with the test and previously trained.
Who interprets the results?
The chest physician is responsible for the results and will make the corresponding report.
What sensations might there be during the test?
There may be cough and very slight feeling of breathlessness. The patient is accompanied by health staff during the whole process.