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Lung Function Tests

Lung Function Tests

Lung function tests can seem confusing and there are so many strange abbreviations. Hopefully this will help.

Lung function tests show how well your lungs work, determine how much air your lungs can hold, how quickly you can move air and in out of your lungs and how well your lungs add oxygen and remove carbon dioxide from your blood. Tests can diagnose lung disease and measure the severity of lung problems. Individual results are best discussed with your own Doctor.


 Measures how much and how quickly you can move air out of your lungs. For the test you breathe into a mouthpiece attached to a recording device (spirometer). The information collected many be printed out onto a sheet (spirogram).

The more common lung function values measured are:


Forced Vital Capacity (FVC) This measures the amount of air you can exhale with force after you inhale as deeply as possible.

Forced Expiratory Volume (FEV) this measures how much air you can expel from your lungs in the first second of breathing out. It can help tell whether your breathing is obstructed by narrowing of the bronchial tubes (as found in asthma or chronic obstructive pulmonary disease (COPD)). The FEV1 is useful in diagnosing COPD, telling how severe it is and how it might develop. The amount of air you exhale may be measured at 1 second (FEV1), 2 seconds (FEV2), or 3 seconds (FEV3).

Peak Expiratory Flow (PEF) This measures how quickly you can exhale.

Maximum Voluntary Ventilation (MVV) This measures the greatest amount of air you can breathe in and out in one minute.

Total Lung Capacity (TLC) This measures the amount of air in your lungs after you inhale as deeply as possible.

Residual Volume (RV) This measures the amount of air in your lungs after you exhale with force.

Other Tests

Gas Diffusion tests These measure the amount of oxygen and other gases that cross the lungs air sacs (alveoli) per minute. The tests evaluate how well gases are being absorbed into your blood stream. Tests include, arterial blood gas which determines the amount of oxygen and carbon dioxide in your blood stream. Carbon monoxide diffusing capacity, which measures how well your lungs transfer a small amount of carbon monoxide into the blood.

Body Plethysmography This measures the total amount of air your lungs can hold. For this you test you sit in an airtight booth and breathe into a mouthpeice whilst pressure and air flow measurements are collected.

Inhalation Challenge tests These are done to identify substances (allegens) that may be causing severe respiratory allergies or asthma.

Exercise Stress tests These evaluate the effect of exercise on lung function tests. Spirometry tests are done before and after exercise and some tests may be done after you inhale medication that enlarges the airways (bronchodilators).

When we exercise, it has an effect on our breathing. When we are physically active, we need to breathe more. To check your breathing, the tester will ask you to do some exercise and take measurements while you're exercising, and afterwards.

This might involve:

  • Walking at your own pace for six minutes, taking as many rests as you need
  • Doing a test called a 'shuttle walking test'. This involves walking between two points set 10 metres (about 30 feet) apart. This is timed with the times gradually get faster, until you can't keep up
  • Walking on a treadmill, while the tester monitors your heart and lungs
  • Doing a test on an exercise bike. This is done occasionally if the doctors need more detailed information about your breathing. Usually you will be asked to breathe through a mouthpiece while you cycle. The amount of oxygen you breathe in and the carbon dioxide you breathe out are measured, as well as your breathing rate, pulse and sometimes your blood gases.

Blood Tests

These are tests to see how well your lungs are getting oxygen into your blood and taking carbon dioxide (a waste gas) out. The simplest test measures how much oxygen is in your blood using an oximeter (pictured) - a little gadget that clips on your fingertip or toe. Sometimes it is attached to a monitor that you wear on your wrist, like a watch. The oximeter doesn't take blood. It shines a light though your fingertip or earlobe, and measures how red your blood is. NB: if you wear nail varnish, this might block the light and affect the reading, so you'll be asked to take it off (on one finger only). To measure carbon dioxide as well as oxygen the tester will need a sample of your blood. She/he will normally take this by putting a small tube in one of the arteries in your arm. Some hospitals check blood gases by taking a blood sample from your earlobe. The blood vessels in your earlobe contain about the same amount of oxygen as blood taken from an artery, but the test is less painful. Your tester wil put special cream on your earlobe which helps increase blood flow. This makes your ear go red and feel hot. She/he will then take the blood sample.

Fitness to Fly test

This test determines a person's oxygen requirements during a flight. A child sits in a booth similar to a telephone booth (mothers go in with babies on their laps). Their oxygen levels are monitored while the level of oxygen in the booth is gradually reduced. This is done by pushing nitrogen gas into the booth (making a constant ffffffffffffffffffffft sound) to replicate the conditions on a plane. The test lasts between 30 – 60 minutes and is quite warm (wear layers to take off) and dull (books, snacks and toys!) but otherwise completely painless.