Spirometry is the most commonly used to test the lung function.

The spirometer measures the speed your lungs can be filled and emptied of air, giving an indication of how well your lungs are performing.

This enables your doctor to make decisions about your lung condition and to plan the best treatment for you.

Spirometry plays an important role in an occupational respiratory health surveillance program. It can assist the health professional by determining if a worker demonstrates a specific pattern of respiratory impairment and can help to assess the effectiveness of measures implemented to protect the individual worker. In addition, results from defined groups of workers can be evaluated in relation to potential workplace hazards. There are various spirometer devices made by different companies, but they all measure the same thing.

They all have a mouthpiece that you use to blow into the device. A doctor or nurse may ask you to blow into a spirometer (spirometry) if you have chest or lung symptoms. Many GP surgeries now have spirometers; small portable devices are available relatively cheaply.In hospitals, the spirometer machinery is more sophisticated and expensive, and can give more detailed results.

How is it done?

It is a simple procedure, you will have your weight and height measured. For the spirometry itself, you need to breathe into the spirometer machine. First you breathe in fully and then seal your lips around the mouthpiece of the spirometer. You then blow out as fast and as far as you can until your lungs are completely empty. This can take several seconds. You may also be asked to breathe in fully and then breathe out slowly as far as you can. The measurements may be repeated two or three times to check that the readings are much the same each time you blow into the machine. Sometimes the tests are performed with you in a separate glass cubicle - this can help get more detailed and precise results. What does the spirometer measure? Spirometry measures the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. The most common measurements used are:

  • Forced expiratory volume in one second (FEV1). This is the amount of air you can blow out within one second. With normal lungs and airways you can normally blow out most of the air from your lungs within one second.
  • Forced vital capacity (FVC). The total amount of air that you blow out in one breath.
  • FEV1 divided by FVC (FEV1/FVC). Of the total amount of air that you can blow out in one breath, this is the proportion that you can blow out in one second.

What can the measurements show?

A spirometry reading usually shows one of four main patterns:

  • Normal.
  • An obstructive pattern.
  • A restrictive pattern.
  • A combined obstructive/restrictive pattern.

Spirometry is a very low-risk test. However, blowing out hard can increase the pressure in your chest, abdomen and eyes. So, you may be advised not to have spirometry if you:

  • Have unstable angina.
  • Have had a recent pneumothorax (air trapped between the outside of the lung and the chest wall - often incorrectly called a punctured lung).
  • Have had a recent heart attack or stroke.
  • Have had recent eye or abdominal surgery.
  • Have coughed up blood recently and the cause is not known.

Reversibility testing

Reversibility testing is done in some cases where the diagnosis of the lung condition is not clear. For this test, you will be asked to do spirometry as described above. You will then be given a medicine by inhaler or nebuliser which may open up the airways. The spirometry test is then repeated 30 minutes or so afterwards. The aim of this is to see if your airways open wider with medication or not. Generally, asthma has more of a reversible element to the airways obstruction, compared with COPD.