Methacholine bronchial provocation test

During the test, the patient inhales progressive doses of a bronchoconstrictor medication called methacholine, which can cause mild narrowing of the airways. This reaction is more pronounced in people with bronchial hyperreactivity, a typical feature of asthma. 

To measure this effect, a technique called spirometry is used, which evaluates lung capacity before and after inhaling methacholine. 

The main parameter analysed is FEV1 (Forced Expiratory Volume in 1 second), a measurement of how much air a person can forcefully exhale in the first second of a forced breath.  

A reduction in FEV1 during the test indicates the bronchi are narrowing in response to methacholine, suggesting bronchial hyperresponsiveness. 

1. Baseline spirometry. Initial lung function is measured to obtain reference values. 

2. Progressive methacholine inhalation. Increasing doses of the drug are administered until the desired maximum concentration is reached, with spirometry performed between each dose to monitor any changes. 

3. Result assessment. If the FEV1 decreases by 20% or more from the initial value, the test is discontinued. This indicates there is bronchial hyperresponsiveness and the test is reported as positive. If the FEV1 does not decrease before the maximum dose is reached, the test is ended and declared as negative.  

4. Reversal of symptoms. At the end of the test, a bronchodilator (e.g., inhaled salbutamol) is administered to restore normal lung function. 

For the test to be reliable, certain inhalers and medications cannot be used in the hours or days beforehand, as these could mask the bronchial response. The medical team will provide clear, personalised instructions for each patient. 

The test is performed by healthcare personnel with specific training in lung function techniques, such as nurses, respiratory physiotherapists and technical specialists. 

The results are interpreted by a pulmonologist, who will integrate this information with your medical history to guide diagnosis or plan the most appropriate treatment. 

Some people experience mild chest tightness or coughing. Such effects are usually mild and short-lived. Healthcare personnel are present at all times to ensure the patient's safety and well-being.