Plethysmography is a technique to evaluate lung function. It yields information not available with more conventional tests like spirometry. It is used to evaluate pulmonary volumes and the resistance of airways to the passage of air.
A body plethysmograph is like a small sealed telephone booth where the patient remains seated breathing through a mouth tube. The patient performs several respiratory manoeuvres, like breathing normally, exhaling forcefully and panting. The volumes and flows of air are recorded and the respiratory function is evaluated.
The test is not painful. Some respiratory manoeuvres can be tiring, and if the patient is very sensitive can feel a bit of claustrophobia. The test may take around 10-15 minutes.
The medication used for asthma may change the results of the test. If you are scheduled for a plethysmography 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.