What Is Pulmonary Function Testing?

Pulmonary function testing, also called lung function testing, is a collection of different tests that determine how well the lungs are working.

Pulmonary function tests check your breathing, including how quickly you inhale and exhale and how much air you are breathing. These tests can also determine whether your lungs are properly delivering oxygen to your blood.

The Role of Pulmonary Function Tests

As important assessments of lung health, pulmonary function tests have many potential uses:

  • 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, dusts, or other lung irritants
  • Evaluating the effectiveness of treatment designed to improve breathing and/or lung health
  • Estimating the risk of lung-related complications before surgery or other treatments that have the potential to impact pulmonary function

Depending on the patient’s circumstances, one or more lung function tests may be prescribed. A health care provider can provide the most detailed information about the goal of pulmonary function testing for any specific patient.

Who should get testing?

Pulmonary function tests are frequently used if you have symptoms that involve a disruption of normal breathing. For example, if you have shortness of breath, a severe or persistent cough, significant congestion or mucus, or chest tightness, your doctor may recommend lung function tests to help diagnose the cause of your symptoms.

You may be more likely to receive lung function tests if you are at higher risk of lung diseases. Examples of risk factors for lung problems include cigarette smoking and exposure to substances that can irritate the lungs, including some chemicals or dusts.

If you have previously been diagnosed with a lung disease, you may have pulmonary function tests to evaluate the severity of the problem, assess your response to treatment, or determine what type of treatment is most appropriate.

Pulmonary function tests generally have few side effects. However, many of these tests require high-effort breathing, which may pose a risk to some patients. In general, pulmonary function tests are not recommended or are performed with caution in people who:

  • 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

You may be less likely to receive pulmonary function tests during outbreaks of respiratory viruses such as COVID-19. Some lung function tests can trigger coughing and spread aerosol particles that may heighten the risk of viral exposure for frontline medical workers. For this reason, testing may be restricted when there is significant community transmission of respiratory viruses.

Getting test results

Depending on the type of lung function test, results are available within a few minutes to a few days. If you are having multiple pulmonary function tests, you may receive results after they have all been completed so that your doctor can consider the information provided by each test before providing an overall assessment. Lung function test results are also interpreted along with other factors such as your symptoms, health history, and findings from other tests.

Many different conditions can cause abnormal results on lung function tests. Testing can help distinguish between different kinds of breathing problems, including:

  • 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.

Many aspects of your health can affect lung health, so pulmonary function tests should always be reviewed with a doctor. A doctor can explain the test result and its significance in your situation.

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.

Lung volume tests

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.

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.

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.

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.

Getting Pulmonary Function Testing

Pulmonary function tests are usually ordered by a doctor. The tests are often conducted in a medical office, hospital, or other clinic with specific devices needed to perform lung function tests.

If you have symptoms that affect your breathing, you should talk with a doctor or nurse to find out what kind of testing is most appropriate and where that testing can be conducted.

In many cases, the doctor will perform several initial tests in order to help determine whether to recommend pulmonary function testing. These tests may include a physical exam, including listening to your lungs with a stethoscope, and a review of your symptoms and overall health.

At-home testing

Although most lung function tests require specialized equipment that is only available in a medical setting, some kinds of tests are able to be performed at home.

For example, pulse oximeters can be purchased without a prescription online or from retail pharmacies. These devices can be clipped on your finger at home and show oxygen saturation in real time. Some doctors may recommend that patients with lung disorders have a pulse oximeter at home to help monitor oxygen levels.

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.

At-home lung function testing should never be done in lieu of consulting with a doctor. In addition, this testing is most safely done under the guidance of a health care professional. A doctor or nurse can make sure that any at-home test is appropriate, review its benefits and downsides, and explain how to understand at-home test results.

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