Lung function tests (also called pulmonary
function tests, or PFTs) check how well your lungs work. The tests determine
how much air your
lungs can hold, how quickly you can move air in and
out of your lungs, and how well your lungs put oxygen into and remove carbon
dioxide from your blood. The tests can diagnose lung diseases, measure the
severity of lung problems, and check to see how well treatment for a lung
disease is working.
Other tests—such as residual volume, gas
diffusion tests, body plethysmography, inhalation challenge tests, and exercise
stress tests—may also be done to determine lung function.
Spirometry is the first and most commonly done lung function
test. It measures how much and how quickly you can move air out of your lungs.
For this test, you breathe into a mouthpiece attached to a recording device
(spirometer). The information collected by the spirometer may be printed out on
a chart called a spirogram.
The more common lung function values
measured with spirometry are:
- Forced vital capacity (FVC). This measures
the amount of air you can exhale with force after you inhale as deeply as
- Forced expiratory volume (FEV).
This measures the amount of air you can exhale with force in one breath. The
amount of air you exhale may be measured at 1 second (FEV1), 2 seconds (FEV2),
or 3 seconds (FEV3). FEV1 divided by FVC can also be
- Forced expiratory flow 25% to 75%. This measures the air flow halfway through an exhale.
- Peak expiratory flow (PEF). This measures
how quickly you can exhale. It is usually measured at the same time as your
forced vital capacity (FVC).
- Maximum voluntary ventilation (MVV). This measures the greatest amount of air you can
breathe in and out during one minute.
- Slow vital capacity (SVC). This measures the amount of air you can slowly exhale
after you inhale as deeply as possible.
- Total lung capacity (TLC). This measures the amount of air in your lungs after you
inhale as deeply as possible.
- Functional residual capacity (FRC). This measures the amount of air in your lungs at the end
of a normal exhaled breath.
- Residual volume (RV). This
measures the amount of air in your lungs after you have exhaled completely. It
can be done by breathing in helium or nitrogen gas and seeing how much is
- Expiratory reserve volume (ERV). This
measures the difference between the amount of air in your lungs after a normal
exhale (FRC) and the amount after you exhale with force (RV).
Gas diffusion tests
Gas diffusion tests measure
the amount of
oxygen and other gases that cross the lungs' air sacs (alveoli ) per minute.
These tests evaluate how well gases are being absorbed into your blood from
your lungs. Gas diffusion tests include:
- Arterial blood gases, which determine
the amount of oxygen and carbon dioxide in your bloodstream.
monoxide diffusion capacity (also called DLCO), which
measures how well your lungs transfer a small amount of carbon monoxide (CO)
into the blood. Two different methods are used for this test. If the
single-breath or breath-holding method is used, you will take a breath of air
containing a very small amount of carbon monoxide from a container while
measurements are taken. In the steady-state method, you will breathe air
containing a very small amount of carbon monoxide from a container. The amount
of carbon monoxide in the breath you exhale is then measured. Diffusing
capacity provides an estimate of how well a gas is able to move from your lungs
into your blood.
Body plethysmography may be
used to measure:
- Total lung capacity (TLC), which is the total amount of air
your lungs can hold. For this test, you sit inside a small airtight room called
a plethysmograph booth and breathe through a mouthpiece while pressure and air
flow measurements are collected.
- Residual volume (RV), which is the
amount of air that remains in your lungs after you exhale as completely as
possible. For this test, you sit inside the plethysmograph booth and breathe
while the pressure of the booth is monitored. You may need to breathe through a
mouthpiece while you are in the booth.
Inhalation challenge tests
Inhalation challenge tests are done to measure the
response of your airways to substances that may be causing
asthma or wheezing. These tests are also called
inhalation testing, increasing amounts of a substance are inhaled through a
nebulizer, a device that uses a face mask or mouthpiece to deliver the
substance in a fine mist (aerosol). Sometimes, increasing amounts of methacholine or mannitol may be inhaled through the nebulizer. Spirometry
readings are taken to evaluate lung function before, during, and after inhaling
In rare cases, a
bronchospasm can occur with inhalation challenge
testing. You will be closely monitored during and after the test.
Exercise stress tests
Exercise stress tests
evaluate the effect of exercise on lung function tests. Spirometry readings are
done after exercise and then again at rest.
Multiple-breath washout test
washout test is done to check lung function in people with cystic fibrosis. For
this test, you breathe air that contains a tracer gas through a tube. Then you
breathe regular air while the amount of tracer gas you exhale is monitored.
Test results are reported as a lung clearance index (LCI). A high LCI value
means that the lungs are not working well.
Lung function results are measured directly in some
tests and are calculated in others. No single test can determine all of the
lung function values, so more than one type of test may be done. Some of the
tests may be repeated after you inhale medicine that enlarges your airways