What is spirometry?
Spirometry is the measurement of the efficiency of the lungs (from the Latin 'spirare' meaning 'to breathe' plus 'metry', 'measurement'). It is one of the standard 'Pulmonary Function Tests' (PFTs) used to determine both the volume of air that the lungs can inhale and exhale, and the rate at which air can be inhaled and exhaled. The device used is called a spirometer, and most modern spirometers are connected to a computer which instantly computes the data from a test.
What does a spirometry test check for?
Spirometry is used to detect the hallmark signs of various types of lung conditions, for example...
- Pulmonary fibrosis
- Cystic fibrosis
- Bronchiectasis - a condition where sections of the airways are wider than they should be
- Interstitial lung disease - diseases affecting the 'interstitium' the network of tissue inside the lungs that supports the air sacs (alveoli); there are a number of these conditions, including interstitial pneumonia, sarcoidosis and asbestosis
- Neuromuscular diseases affecting the respiratory muscles (muscular dystrophy is a neuromuscular condition)
It is used to check causes of chronic cough and - in combination with a bronchodilator - to diagnose asthma and COPD, and to check whether a patient's condition will respond to medication (see below).
What is a bronchodilator?
A bronchodilator is an agent which acts to dilate, or enlarge or widen, the bronchi and the bronchioles. The bronchi are the two tubes that feed air into the lungs and the bronchioles are the much narrower tubes that carry this air to (and from) the air sacs in the lungs.
Bronchodilators are naturally produced by the body (called 'endogenous bronchodilators') and can be manufactured synthetically to be given to patients as medication, to treat conditions that cause airway narrowing. As a medication it is often referred to colloquially as a 'puffer'.
Bronchodilator medication can either be short acting, that is provide a quick form of relief of a short term problem with breathing, or they can be long acting, used as preventative medicine for people that are prone to breathing difficulties. Those used in spirometry testing are short-acting bronchodilators.
What is involved in the pre and post bronchodilator spirometry test?
In a process known as 'reversibility testing', the patient breathes in and out through a mouthpiece (with a nose clip in place) and, after a few breaths, is asked to breathe in as much as they can, before breathing out as hard and as fast as they can until they can't breathe out any more. This is the pre- bronchodilator reading.
After this a bronchodilator (generally salbutamol) is administered and the test is performed again. An improvement of 12% (and 200ml) or more in lung function after taking the bronchodilator indicates that the patient should respond well to medication.
Spirometry is also used to monitor existing lung conditions and to test the effectiveness of medications.
Do I need to prepare for a spirometry test?
Do not wear constrictive clothing, as this can stop you from taking a deep breath and do not eat a large meal in the two hour period before taking the test as this will also restrict your ability to breathe in fully.