Pulmonary Function Tests

A complete measure of how well your lungs are working

What are pulmonary function tests (PFTs)?

Pulmonary function tests (PFTs) are a group of tests that measure how well your lungs work. This includes how well you’re able to breathe and how effective your lungs are able to bring oxygen to the rest of your body.

Your doctor may order these tests:
      • If you’re having symptoms of lung problems
      • If you’re regularly exposed to certain substances in the environment or workplace
      • Monitor the course of chronic lung disease, such as asthma or chronic obstructive pulmonary disease (COPD)
      • Assess how well your lungs are working before you have surgery

PFTs are also known as lung function tests.

Why are these tests done?

Your doctor will order these tests to determine how your lungs are working. If you already have a condition that’s affecting your lungs, your doctor may order this test to see if the condition is progressing or how it’s responding to treatment.

PFTs can help diagnose:

How do I prepare for pulmonary function tests?

If you’re on medications that open your airways, such as those used for asthma or chronic bronchitis, your doctor may ask you to stop taking them before the test. If it isn’t clear whether or not you should take your medication, make sure to ask your doctor. Pain medications may also affect the results of the test. You should tell your doctor about any over-the-counter and prescription pain medications you’re taking.

It’s important that you don’t eat a large meal before testing. A full stomach can prevent your lungs from inhaling fully. You should also avoid food and drinks that contain caffeine, such as chocolate, coffee, and tea, before your test. Caffeine can cause your airways to be more open which could affect the results of your test. You should also avoid smoking at least an hour before the test, as well as strenuous exercise before the test.

Be sure to wear loose-fitting clothing to the test. Tighter clothing may restrict your breathing. You should also avoid wearing jewelry that might affect your breathing. If you wear dentures, wear them to the test to ensure that your mouth can fit tightly around the mouthpiece used for the test.

If you have had recent eye, chest, or abdominal surgery or a recent heart attack, you will likely need to have a test.

What happens during the tests?

  • Spirometry
  • Plethysmography Test
  • Diffusion Capacity Test
  • What is Lung Diffusion?
  • What is Lung Diffusion Testing?
  • What is the Purpose of Lung Diffusion Testing?
  • How Should I Prepare for a Lung Diffusion Test?
  • What Should I Expect During a Lung Diffusion Test?

Your PFTs may include spirometry, which measures the amount of air you breathe in and out. For this test, you’ll sit in front of a machine and be fitted with a mouthpiece. It’s important that the mouthpiece fits snugly so that all the air you breathe goes into the machine. You’ll also wear a nose clip to keep you from breathing air out through your nose. The respiratory technologist will explain how to breathe for the test.

You may then breathe normally. Your doctor will ask you to breathe in and out as deeply or as quickly as you can for several seconds. They may also ask you to breathe in a medication that opens your airways. You’ll then breathe into the machine again to see if the medication affected your lung function.

Plethysmography Test

A plethysmography test measures the volume of gas in your lungs, known as lung volume. For this test, you’ll sit or stand in a small booth and breathe into a mouthpiece. Your doctor can learn about your lung volume by measuring the pressure in the booth.

Diffusion Capacity Test

This test evaluates how well the small air sacks inside the lungs, called alveoli, work. For this part of a pulmonary function test, you will be asked to breathe in certain gases such as oxygen, helium, or carbon dioxide.

You may also breathe in a “tracer gas” for one breath. The machine can detect when you breathe out this gas. This tests how well your lungs are able to transfer oxygen and carbon dioxide to and from your bloodstream.

What is Lung Diffusion?

From asthma to chronic obstructive pulmonary disease (COPD), there are a variety of conditions that can affect the lungs. Wheezing or general shortness of breath may be signs that the lungs aren’t functioning exactly as they should be. If you exhibit signs of lung problems, your doctor may order tests to assess lung function.

One of these tests is a lung diffusion test. A lung diffusion test is used to examine how your lungs are processing air. Along with other tests, it can help your doctor determine whether your respiratory system is working properly and efficiently. It may also be known as a diffusing capacity of the lung for carbon monoxide (DLCO) test.

What is Lung Diffusion Testing?

Lung diffusion testing is designed to test how well your lungs allow oxygen and carbon dioxide to pass in and out of your blood. This process is called diffusion.

When you breathe, you inhale air containing oxygen through your nose and mouth. This air travels down your trachea, or windpipe, and into your lungs. Once in the lungs, the air travels through a series of increasingly smaller structures called bronchioles. It eventually reaches tiny sacs called alveoli.

From the alveoli, the oxygen from the air you breathe enters your blood in nearby blood vessels. This is a process called oxygen diffusion. Once your blood is oxygenated, it carries oxygen throughout your body.

Another form of diffusion occurs when blood containing carbon dioxide travels back to your lungs. The carbon dioxide moves from your blood to your alveoli. It’s then expelled through exhalation. This is a process called carbon dioxide diffusion.

Lung diffusion testing can be used to analyze both oxygen and carbon dioxide diffusion.

What is the Purpose of Lung Diffusion Testing?

Doctors typically use lung diffusion testing to assess people who have lung disease or to help diagnose such diseases. Proper assessment and diagnosis is essential for providing the optimal treatment.

If you show symptoms of lung disease, lung diffusion testing may be used to analyze how your lungs are functioning. Also, if you’re undergoing treatment for lung disease, your doctor may order this test from time to time to monitor the disease’s progress and how well your treatment is working.

How Should I Prepare for a Lung Diffusion Test?

Before the test, your doctor may ask you to take certain steps to prepare for a lung diffusion test. You may be asked to:

  • Avoid using a bronchodilator or other inhaled medications prior to testing
  • Avoid eating a large amount of food before the test
  • Avoid smoking for several hours before the test
What Should I Expect During a Lung Diffusion Test?

In most cases, a lung diffusion test involves the following steps:

  1. A mouthpiece will be placed around your mouth. It will fit snugly. Your doctor will place clips on your nose to prevent you from breathing through your nostrils.
  2. You’ll take a breath of air. This air will contain a tiny, and safe, amount of carbon monoxide.
  3. You’ll hold this air for a count of 10 or so.
  4. You’ll quickly exhale the air you’re holding in your lungs.
  5. This air will be collected and analyzed.

About us

North Toronto Sleep Centre is an accredited IHF sleep diagnostic centre, overseen by the Ministry of Health and Long Term Care, also governed by the CPSO.

4040 Finch Avenue E., Suite 108,
Scarborough, ON  M1S 4V5
Tel: (416) 293-3233  |  Fax: (416) 293-0692


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