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 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, and chronic obstructive pulmonary disease (COPD).
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 well your lungs deliver oxygen to your blood.
· How strong your breathing muscles are.
Breathing Tests
The breathing tests most often used are:
· Spirometry. 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 that’s 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 what’s 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.
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 age 6, if they can
follow directions well. Spirometry may be tried in children as young as age 5.
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 age 2) 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 age 5, 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 five 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.