Lung function tests, also called pulmonary function tests, measure the size of a person's lungs, how much air can be breathed in and out, how fast air can be breathed out, and how well the person's lungs deliver oxygen to the blood.

 

Lung function tests are used to look for the cause of breathing problems, such as 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 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. 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 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.

 

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.

 

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.

 

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 light-headed, 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.

 

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 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.

 

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.