How Is a Pulmonary Function Test Performed?

Four common types of lung tests are spirometry, lung volume test, gas diffusion test, and exercise stress test.

Pulmonary function test or lung function test is a group of tests that check the workings of the lungs. They are noninvasive test which can determine the functional status of the lung cells and how well the lungs are working. 

The tests look for:

• How much air can lungs hold?
• How well can air move in and out of the lungs?
• How well the lungs move oxygen the into bloodstream. 

There are several types of lung tests. They include:

• Spirometry: The most common type of lung function test. It measures how much and how quickly air can move in and out of the lungs.
• Lung volume test: It is also known as body plethysmography. This test measures the amount of air an individual can hold in the lungs and the amount of air that remains after exhalation (breathing out).
• Gas diffusion test: This test measures how oxygen and other gases move from the lungs to the bloodstream.
• Exercise stress test: This test looks at how exercise affects lung function.

These tests may be used singly or together, depending on specific symptoms or conditions.

Below are the steps for the most common four types of lung function tests.

For a spirometry test:

• The patient is asked to sit on a chair and a soft clip will be put on the nose. This is done so that patient breathes through the mouth, rather than your nose.
• The patient is asked to place lips tightly around the mouthpiece and breathe in and out as instructed. 
• The spirometer will measure the amount and rate of airflow over a period of time.

For a lung volume (body plethysmography) test:

• The patient asked to sit in a clear, airtight room that looks like a telephone booth.
• The patient may wear a nose clip and place lips around a mouthpiece connected to a machine.
• The patient is asked to breathe in and out as instructed.
• The pressure changes inside the room help measure lung volume.

For a gas diffusion test:

• The patient may wear a mouthpiece connected to a machine.
• They may be asked to inhale (breathe in) a very small, non-dangerous amount of carbon monoxide or other types of gas.
• Measurements will either be taken as they breathe in and out.
• The test can show how effective the lungs are functioning by moving gases to the bloodstream.

For an exercise test: 

• The patient may be asked to ride a stationary bike or walk on a treadmill.
• They may be attached to monitors and machines that will measure blood oxygen, blood pressure, and heartbeat.
• This test shows how well the lungs perform during exercise.

Your doctor may order pulmonary function tests to:

• Find the cause of breathing problems
• Diagnose and monitor chronic lung diseases, including asthma, chronic obstructive pulmonary disease (COPD) and emphysema
• See if lung disease treatments are working
• Check lung function before surgery
• Check whether exposure to chemicals or other substances in the home or workplace has caused lung damage.

Testing pulmonary function tests can help doctors diagnose other conditions such as:

• Thickened, stretched, or enlarged airways
• Thickening or hardening of your connective tissues (scleroderma)
• The weakness of the muscles in the wall of the chest
• Diseases of the air exchange units of the lung (alveolar membrane)

If a patient has abnormal lung function test results they might have a lung disease. There are two main types of lung diseases that can be diagnosed with a lung function test:

• Obstructive diseases: These diseases cause airways to become narrow, making it hard for air to flow out of the lungs. Obstructive lung diseases include asthma, bronchitis, and emphysema.
• Restrictive diseases: In these diseases, the lungs or chest muscles aren't able to expand enough. This reduces airflow and the ability to send oxygen into the bloodstream. Restrictive lung disorders include scleroderma, sarcoidosis, and pulmonary fibrosis.
• Mixed pattern: Sometimes, a disease may be a combination of obstructive and restrictive patterns, this may need a different management protocol.