Pulmonary Function Test
Overview
Why it’s done?
- Diagnosing the underlying cause of health problems affecting the lungs, including asthma, chronic obstructive pulmonary disease (COPD), and other conditions, in people who have symptoms that affect breathing.
- Measuring the disease severity in many lung conditions, including how much these conditions affect oxygen levels in the blood, which helps doctors estimate the likely course of a disease and determine the optimal treatment plan.
- Detecting lung damage in people who have been exposed to certain chemicals, dust, or other lung irritants.
- Evaluating the effectiveness of treatment designed to improve breathing and/or lung healthtants.
- Estimating the risk of lung-related complications before surgery or other treatments that have the potential to impact pulmonary function
Who should get testing?
- Have certain heart diseases, very high blood pressure, or have had major heart problems in recent weeks
- Have recently had surgery in the abdomen, chest, or head and neck area
- Have an elevated risk of a collapsed lung
- Have very high blood pressure
Results
- Obstructive disorders, which involve disruptions when exhaling. These disruptions can include difficulty breathing out all the air in the lungs or exhaling too slowly. Asthma, COPD, and lung infections are examples of obstructive lung conditions.
- Restrictive disorders, which involve reductions in the amount of air you can inhale or hold in your lungs. Scarring of the lungs can make the lungs smaller and is an example of a restrictive disorder. Weakness in the muscles that control breathing can also cause restrictive lung problems.
- Mixed disorders, which involve both obstructive and restrictive breathing problems.
The results of lung function tests can detail specific aspects of your breathing and help assess whether your lungs are delivering the amount of oxygen to the blood that your body needs to work properly.
Types of Pulmonary Function Tests
Pulmonary function testing can include several distinct tests. Each test can provide different information about how the lungs are working.A doctor may recommend one or more pulmonary function tests depending on the situation.
The following sections provide an introduction to the types of pulmonary function tests
Spirometry
Spirometry is used to measure the amount of air you can breathe out and how quickly it is exhaled. This test can play an essential role in identifying obstructive lung disorders.
To take the test, you breathe in deeply and then exhale into a tube as hard as you can. The tube is attached to a device called a spirometer that takes measurements about the strength and speed of your exhalation.
If your initial spirometry test is abnormal, the doctor may give you medicine through an inhaler. After a few minutes, you will take the spirometry test again to see if the medication improved your breathing.
Spirometry
A lung volume test is used to see how much air you can hold in your lungs.
The most common type of lung volume test is known as body plethysmography. In this test, you sit in a room that resembles a phone booth. You use a mouthpiece to breathe in and out, and the test measures changes in air pressure inside the room. These changes demonstrate your lung capacity.
A gas dilution test is another kind of lung volume test. In this test, you breathe in and inhale from a chamber that holds a harmless gas like nitrogen or helium. The change in the amount of gas in the chamber reflects your lung volume.
In some cases, imaging tests like a chest x-ray or chest CT scan can also be used to evaluate total lung volume.
Diffusion capacity test
A diffusion capacity test is designed to determine how well the lungs are delivering oxygen to the blood.
In a diffusion capacity test, you inhale and exhale through a mouthpiece. When you inhale, you breathe in a small amount of a harmless “tracer gas.” When you exhale, the amount of the gas is measured. The difference between how much of the gas you inhale and how much you exhale helps estimate how effectively your lungs are absorbing oxygen when you breathe.
Arterial blood gases test
Unlike many other pulmonary function tests, an arterial blood gas test does not involve breathing into a tube. Instead, it uses a blood sample to see how much oxygen and carbon dioxide is in your blood.
Taking this test requires inserting a needle into an artery to withdraw a vial of blood. Normally the sample is taken from an artery in your wrist. Reduced oxygen or increased carbon dioxide in your blood can be a reflection of impaired pulmonary function.
Pulse oximetry
Pulse oximetry is another method for assessing oxygen saturation, which is the amount of oxygen in your blood.
In this test, a device called a pulse oximeter clips onto your fingertip or earlobe. This device includes a sensor that monitors your pulse and estimates your oxygen saturation. As part of pulmonary function testing, you may be asked to use the device at various points in time or while engaging in different levels of physical activity.
As with an arterial blood gases test, pulse oximetry can help evaluate whether your lungs are providing enough oxygen to your blood.
Maximal respiratory pressures test
Testing maximal respiratory pressures is a method of determining whether there is weakness in your breathing muscles.
To take this test, you inhale or exhale through a mouthpiece that is blocked. A device measures the pressure when breathing in, known as maximal inspiratory pressure, and when breathing out, which is maximal expiratory pressure.
Exercise tests
Some pulmonary function tests involve seeing how your breathing, heart rate, and oxygen saturation change when you are physically active.
A common exercise test is the 6-minute walk test, which involves walking in a flat, straight hallway for six minutes. Measurements are taken while you walk to evaluate lung function. An incremental shuttle walk test lasts 12 minutes and involves walking between cones that are placed 10 meters apart. As the test goes on, you are instructed to increase your walking speed.
Fractional exhaled nitric oxide test
A test of fractional exhaled nitric oxide (FeNO) is used to check for inflammation in the lungs. It is often used to assess asthma and to see how well asthma medications are working.
To take a FeNO test, you breathe out steadily through a mouthpiece. The mouthpiece is connected to a device that analyzes the amount of nitric oxide in your breath. High amounts of nitric oxide are associated with increased lung inflammation.
An endurance shuttle walk test evaluates how long you can continue to walk at a certain level of physical effort. The test involves moving between cones that are 10 meters apart while you receive instructions for how quickly to walk. The test continues until 20 minutes have passed or until you are not able to continue walking at the specified pace.
Less often, exercise tests of lung function may involve walking quickly, running on a treadmill, or riding on a stationary bicycle.
At-home testing
At-home spirometers are available for patients with some lung diseases. In most cases, these involve a tube attached to a small portable device. New approaches have also enabled some at-home spirometry to be performed with the assistance of a tablet or smartphone.