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 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.

(For more information on healthy lung function, see the Diseases and Conditions Index "How the Lungs Work" article.)

February 2008