Lung function tests enable measurement of your breathing capacity and airway function. They can help establish the cause of your symptoms, are useful for monitoring some conditions, particularly a chronic illness, and can be reassuring if you are concerned about your health especially if the results are normal.
Your tests will be described in detail by the technician at the hospital. You will need to blow into a machine usually by putting a mouthpiece in your mouth, like a snorkel. You will usually have to do this several times. You may be asked to wear a nose-clip.
The tests should take between 30 minutes and one hour. If you are very breathless, they may take longer. You may also need a ‘reversibility test’. This involves giving you a dose of an inhaled drug often used in asthma (salbutamol); the tests may be repeated to assess whether they are different in response to the medication. This test can be useful to establish whether there is a significant asthmatic component to your symptoms.
Peak flow: Measures the fastest speed you can blow out. To do the test you take the biggest breath in that you can and then blow out as fast as you can. The results are useful in diagnosing asthma and deciding on its treatment. This test can usually be performed in the clinic and does not need specialist equipment.
Spirometry test: Measures your FEV1 (forced expiratory volume in 1 second). This is a useful way of assessing airway calibre. It is most often affected by smoking and asthma. It can also give an estimate of your vital capacity which is a marker of lung size.
Lung volumes: Measure the size of the lungs in more detail. These tests use helium gas, which is not absorbed into the body. It allows the technician to work out parameters such as total lung capacity.
Transfer factor: Measures how well your lungs can extract a substance from the air you breathe, and transfer it to the blood stream. To do this a very small dose of carbon monoxide is given to you with helium. There are usually no side effects from either of these gases.
Oximetry: Measures the concentration of oxygen in the blood via a probe on the finger.
Occasionally other tests of respiratory function may be necessary. These may have to be performed in the hospital, such as taking blood directly from your artery to measure carbon dioxide levels (an arterial blood gas).