What Are Lung Function Tests?
Lung function tests measure the size of your lungs,
how much air you can breathe in and out, how fast you can breathe air out, and
how well your lungs deliver oxygen to your blood. These tests also are called
pulmonary (PULL-mun-ary) function tests.
Lung function tests are used to look for the cause
of breathing problems (like shortness of breath). These tests are used to check
for conditions such as
asthma,
lung
tissue scarring,
sarcoidosis
(sar-koy-DO-sis), and
COPD
(chronic obstructive pulmonary disease).
Lung function tests also are used to see how well
treatments for breathing problems, such as asthma medicines, are working. The
tests may be used to check on whether a condition, such lung tissue scarring,
is getting worse.
Overview
Lung function tests measure:
- How much air you can take into your lungs. This
amount is compared to that of other people your age, height, and sex. This
allows your doctor to see whether you're in the normal range.
- How much air you can blow out of your lungs and
how fast you can do it.
- How well your lungs deliver oxygen to your
blood.
- How strong your breathing muscles are.
Breathing Tests
The breathing tests most often used are:
- Spirometry (spi-ROM-eh-tre). This test measures
how much air you can breathe in and out. It also measures how fast you can blow
air out.
- Peak flow meter. This meter is a small, hand-held
device thats sometimes used by people who have asthma. The meter helps
track their breathing.
- Lung volume measurement. This test, in addition
to spirometry, measures how much air you have left in your lungs after you
breathe out completely.
- Lung diffusing capacity. This test measures how
well oxygen passes from your lungs to your bloodstream.
These tests may not show whats causing
breathing problems. Other tests, such as a cardiopulmonary exercise test, also
may be done. This test measures how well your lungs and heart work while you
exercise on a treadmill or bicycle.
Tests To Measure Oxygen Level
Pulse oximetry and arterial blood gas are two tests
used to measure the oxygen level in the blood. They're also called blood oxygen
tests.
Pulse oximetry measures blood oxygen levels using a
special light. During an arterial blood gas test, your doctor inserts a small
needle into an artery, usually in your wrist, and takes a sample of blood. The
oxygen level of the blood sample is then checked.
Outlook
Lung function tests usually are painless and rarely
cause side effects. You may feel some discomfort during the arterial blood gas
test when the needle is inserted into the artery.
(For more information on healthy lung function, see
the Diseases and Conditions Index "How the Lungs Work" article.)
Types of Lung Function Tests
Breathing Tests
Spirometry
Spirometry measures how much air you breathe in and
out and how fast you blow it out. This is measured in two ways: peak expiratory
flow rate (PEFR) and forced expiratory volume in 1 second (FEV1).
PEFR refers to the amount of air you can blow air out as quickly as possible.
FEV1 refers to the amount of air you can blow out in 1 second.
During the test, a technician will ask you to take a
deep breath in and then blow as hard as you can into a tube connected to a
small machine. Your doctor may have you inhale a medicine that helps open your
airways. He or she will want to see whether the medicine changes or improves
the test results.
Spirometry is done to look for diseases and
conditions that affect how much air you can breathe in, such as
sarcoidosis
or lung
tissue scarring. It's also done to look for diseases that affect how fast
you can breathe air out, like
asthma
and
COPD
(chronic obstructive pulmonary disease).
Peak Flow Meter
A peak flow meter is a small, hand-held device that
you blow into. It shows how well air moves out of your lungs. People who have
asthma sometimes use this device. It helps them (and their doctors) check their
breathing. A peak flow meter can be used at home or in a doctor's office.
Lung Volume Measurement
This test measures the size of your lungs and how
much air you can breathe in and out. During the test, you sit inside a glass
booth and breathe into a tube that's hooked to a computer.
Sometimes you breathe in nitrogen or helium gas and
then blow it out. The gas you breathe out is then measured to test how much air
your lungs can hold.
The test can help diagnose lung tissue scarring or a
stiff and/or weak chest wall.
Lung Diffusion Capacity
This test measures how well oxygen passes from your
lungs to your bloodstream. During this test, you breathe in a gas through a
tube. You hold your breath for a brief moment and then blow the gas out.
Abnormal test results may suggest loss of lung
tissue, emphysema (a type of COPD), very bad scarring, or problems with blood
flow through the body's arteries.
Tests To Measure Oxygen Level
Pulse oximetry and arterial blood gas tests show how
much oxygen is in your blood. During pulse oximetry, a small light is placed
over your fingertip, earlobe, or toe to measure the oxygen. This test is
painless and no needles are used.
During an arterial blood gas test, your doctor
inserts a small needle into an artery, usually in your wrist. He or she takes a
sample of blood. The oxygen level of the blood is checked in a lab.
Testing in Infants and Young Children
Spirometry and other measures of lung function
usually can be done in children older than 6 years, if they can follow
directions well. Spirometry may be tried in children as young as 5 years.
However, technicians who have special training with young children may need to
do the testing.
Instead of spirometry, a growing number of medical
centers measure respiratory system resistance. This is another way to test lung
function in young children.
The child wears nose clips and has his or her cheeks
supported with an adult's hands. The child breathes in and out quietly on a
mouthpiece, while the technician measures changes in pressure at the mouth.
During these lung function tests, parents can help comfort their children and
encourage them to cooperate.
Very young children (younger than 2 years) may need
an infant lung function test. This requires special equipment and medical
staff. This type of test is only available at a few centers. The doctor gives
the child medicine to help him or her sleep through the test.
A technician places a mask over your child's nose
and mouth and a vest around your child's chest. The mask and vest are attached
to a lung function machine. The machine gently pushes air into your child's
lungs through the mask. As your child exhales, the vest slightly squeezes his
or her chest. This helps push more air out of the lungs. The exhaled air is
then measured.
In children younger than 5 years, the doctor likely
will use signs and symptoms, medical history, and a physical exam to diagnose
lung problems.
Pulse oximetry and arterial blood gas tests may be
used for children of all ages.
Other Names for Lung Function Tests
- Lung diffusion testing; also called diffusing
capacity and diffusing capacity of the lung for carbon monoxide, or DLCO
- Pulmonary function tests, or PFTs
Arterial blood gas tests also are called blood gas
analyses, or ABGs.
Who Needs Lung Function Tests?
People who have breathing problems, such as
shortness of breath, may need lung function tests. These tests help find the
cause of breathing problems. They're used to check for conditions such as
asthma,
lung
tissue scarring,
sarcoidosis,
and
COPD
(chronic obstructive pulmonary disease).
Lung function tests also are used to see how well
treatments for breathing problems, such as asthma medicines, are working.
Diagnosing Lung Conditions
Your doctor will diagnose a lung condition based on
your medical history, a physical exam, and test results.
Medical History
Your doctor will ask you questions, such as:
- Do you ever feel like you can't get enough air?
- Does your chest feel tight sometimes?
- Do you have periods of coughing or wheezing (a
whistling sound when you breathe)?
- Do you ever have chest pain?
- Can you walk or run as fast as other people your
age?
Your doctor also will ask if you or anyone in your
family has ever:
- Had asthma and/or allergies
- Had heart disease
- Smoked
- Traveled to places where you may have been
exposed to tuberculosis
- Had a job that exposed you to dust, fumes, or
particles (like asbestos)
Physical Exam
Your doctor will measure your heart rate, breathing
rate, and blood pressure. He or she also will listen to your heart and lungs
with a stethoscope and feel your abdomen and limbs.
Your doctor will look for signs of heart or lung
disease, or another disease that could cause your symptoms.
Lung and Heart Tests
Based on your medical history and physical exam,
your doctor will decide what tests you need. A
chest x ray usually is the first test done to find the cause
of breathing problems. This test takes pictures of the organs and structures
inside your chest.
Your doctor may do lung function tests to find out
even more about how well your lungs work.
Your doctor also may do tests to check your heart,
such as an
EKG
(electrocardiogram) or a
stress
test. An EKG detects and records your heart's electrical activity. A stress
test shows how well your heart works during physical activity.
What To Expect Before Lung Function Tests
If you take breathing medicines, your doctor may ask
you to stop them for a short time before spirometry, a lung volume measurement
test, or a lung diffusion capacity test.
No special preparation is needed before pulse
oximetry and arterial blood gas tests. If you're being treated with oxygen,
your doctor may ask you to stop using it for a short time before the tests.
This is done to check your blood oxygen level without the added oxygen.
What To Expect During Lung Function Tests
Breathing Tests
Spirometry tests may be done in your doctor's office
or in a special lung function lab. Your doctor may ask you to use a peak flow
meter in the office and suggest that you also do the test at home. The lung
volume measurement and lung diffusion capacity tests are done in a special lab
or clinic.
For the lung volume measurement and lung diffusion
capacity tests, you sit in a chair next to a machine that measures your
breathing. For spirometry, you sit or stand next to the machine.
Before the tests, a technician places soft clips on
your nose. This allows you to breathe only through a tube that's attached to
the testing machine. The technician will tell you how to breathe into the tube.
For example, you may be asked to breathe normally, slowly, or rapidly.
The deep breathing done in some of the tests may
make you feel short of breath, dizzy, or lightheaded, or it may make you cough.
Spirometry
In this test, you take a deep breath and then exhale
as fast and as hard as you can into the tube. With spirometry, your doctor may
give you a medicine that helps open your airways. Your doctor will want to see
whether it changes or improves the test results.
Peak Flow Meter
In this test, you take a deep breath and then exhale
as fast and as hard as you can into a small, hand-held device that's connected
to a mouthpiece.
Lung Volume Measurement
For this test, you sit in a clear glass booth and
breathe through the tube attached to the testing machine. The changes in
pressure inside the booth are measured to show how much air you can breathe
into your lungs.
Sometimes you breathe in nitrogen or helium gas and
then breathe it out. The gas that you exhale is then measured.
Lung Diffusion Capacity
During this test, you breathe in gas through the
tube, hold your breath for 10 seconds, and then rapidly blow it
out. The gas contains a small amount of carbon monoxide, which won't harm you.
Tests To Measure Oxygen Level
Pulse oximetry is done in a doctor's office or
hospital. Arterial blood gas tests are done in a lab or hospital.
Pulse Oximetry
During this test, a small light is placed over your
fingertip, earlobe, or toe using a clip or flexible tape. It's then attached to
a cable that leads to a small machine called an oximeter. The oximeter shows
the amount of oxygen in your blood. This test is painless and no needles are
used.
Arterial Blood Gas
During this test, your doctor or technician inserts
a small needle into an artery, usually in your wrist, and takes a sample of
blood. You may feel some discomfort when the needle is inserted. The oxygen
level of the blood sample is then checked in a lab.
After the needle is removed, you may feel mild
pressure or throbbing at the needle site. Applying pressure to the area for 5
to 10 minutes should stop the bleeding. You will be given a small bandage to
place on the area.
What To Expect After Lung Function Tests
You can return to your normal activities and restart
your medicines after lung function tests. Talk to your doctor about when you'll
get the test results.
What Do Lung Function Tests Show?
Breathing Tests
Spirometry
Spirometry can show whether you have:
- Blockage (obstruction) in your airways. This may
be a sign of
asthma,
COPD
(chronic obstructive pulmonary disease), or another obstructive lung condition.
- Smaller than normal lungs (restriction). This may
be a sign of
heart
failure, damage or
scarring
of the lung tissues, or another restrictive lung condition.
Peak Flow Meter
A peak flow meter shows the fastest rate at which
you can blow air out of your lungs. People who have asthma use this device to
help track their breathing.
Lung Volume Measurement
This test shows the size of your lungs. Abnormal
test results may show that you have lung tissue scarring or a stiff chest
wall.
Lung Diffusion Capacity
This test can show a problem with oxygen moving from
your lungs into your bloodstream. This may be a sign of loss of lung tissue,
emphysema (a type of COPD), or problems with blood flow through the body's
arteries.
Tests To Measure Oxygen Level
Pulse oximetry and arterial blood gas tests measure
the oxygen level in your blood. These tests show how well your lungs are taking
in oxygen and moving it into the bloodstream. A low level of oxygen in the
blood may be a sign of a lung or heart condition.
What Are the Risks of Lung Function Tests?
Breathing Tests
Spirometry, peak flow meter, lung volume
measurement, and lung diffusion capacity tests usually are safe. These tests
rarely cause problems.
Tests To Measure Oxygen Level
Pulse oximetry has no risks. Side effects from
arterial blood gas tests are rare.
Key Points
- Lung function tests measure the size of your
lungs, how much air you can breathe in and out, how fast you can breathe air
out, and how well your lungs deliver oxygen to your blood.
- Lung function tests are used to look for the
cause of breathing problems (like shortness of breath). These tests are used to
check for conditions such as
asthma,
lung
tissue scarring, and
COPD
(chronic obstructive pulmonary disease). They're also used to see how well
treatments for breathing problems, such as asthma medicine, are working.
- Lung function tests look at how much air you can
take into your lungs, how much air you can blow out of your lungs and how fast
you can do it, how well your lungs deliver oxygen to your blood, and how strong
your breathing muscles are.
- Breathing tests include spirometry, peak flow
meter, lung volume measurement, and lung diffusion capacity. Pulse oximetry and
arterial blood gas tests are used to measure the oxygen level in your blood.
- People who have breathing problems, such as
shortness of breath, may need lung function tests. These tests help find the
cause of the breathing problems.
- If you take breathing medicines, your doctor may
ask you to stop them for a short time before spirometry, a lung volume
measurement test, or a lung diffusion capacity test. No special preparation is
needed before pulse oximetry and arterial blood gas tests.
- For breathing tests, you will breathe through a
tube that's attached to a testing machine. You may be asked to breathe
normally, slowly, or rapidly. You also may be asked to inhale and then exhale a
small amount of gas.
- For the tests that measure oxygen level in the
blood, either a small light will be attached to your fingertip, earlobe, or toe
to measure the oxygen level, or your doctor will take a small sample of your
blood to measure the oxygen level.
- You can return to your normal activities and
restart your medicines after lung function tests. Talk to your doctor about
when you'll get the test results.
- Lung function tests can show whether you have
signs of a lung or heart condition. These tests also can show how well
treatments for breathing problems, such as asthma medicines, are working.
- Lung function tests are painless and rarely cause
side effects. You may feel some discomfort during the arterial blood gas test
when the needle is inserted into the artery.
Links to Other Information About Lung Function
Tests
NHLBI Resources
Non-NHLBI Resources
Clinical Trials
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