The official blog of the Lung Institute.
What is the Diffusing Capacity Test?
Oxygen is the life source for your organ’s cells. It helps the cells breakdown much needed energy from the food you eat. A lack of oxygen leads to a decrease in functioning, cells dying and eventually complete organ failure. Luckily, we have an amazing system in the human body that continually supplies our organs with fresh oxygen while retrieving the byproduct of energy creation: carbon dioxide. Of course, this is our cardiovascular system, which gets the oxygen from the lungs. Lungs pull-in oxygen from the air, but it’s what happens next that is truly amazing. This vital organ diffuses the oxygen into the blood vessels. When you suffer from a lung disease like chronic obstructive pulmonary disease (COPD) or interstitial lung disease (ILD), lung function decreases greatly. When diagnosed with a lung disease, typically a pulmonary function test (PFT) is performed. Another test that measures the lungs’ ability to diffuse oxygen into the bloodstream is called the diffusing capacity test.
How is Diffusing Capacity Tested?
The first step in judging the diffusing capacity of the lungs is understanding the overall volume and capacity of the lungs. This can be done with a fairly simple test. Once completed, the diffusing capacity test can be conducted.
Sometimes the test will be performed by a pulmonologist, or a lung care specialist. The physician will have you inhale through a mouthpiece that fits snuggly around your mouth. You will need to put a clamp over your nose so that other air cannot be inhaled during the test. The air mixture you inhale contains a small amount of a specific chemical known as the tracer. The chemical is not harmful to your lungs. Then, after about 10 seconds of holding your breath, you will exhale back into the mouthpiece. Most tests are performed using a single breath.
When you inhale the air mixture and hold it for 10 seconds, the chemical compound is being absorbed into the thin membrane of the lungs’ air sacs known as the alveoli. This is where the gas exchange in the lungs happens. When you exhale, any amount of the tracer chemical that wasn’t absorbed into the alveoli membrane will be expelled back into the mouthpiece. The computer will then compare the original amount of the tracer against the amount that was returned. The end number will indicate to the physician how efficient your lungs are at absorbing oxygen.
Factors that Affect Your Results
People with lung disease will likely see a low percentage of the tracer gas being absorbed. This can be caused by multiple factors. The airways are commonly inflamed in a person with lung disease, causing a lack of ability to inhale normal quantities of air. Also, many lung conditions can result in mucus build-up in the alveoli. This causes the thin membrane that exchanges oxygen for carbon dioxide to thicken, greatly reducing the ability to exchange or diffuse the chemicals.
Your height, age, gender and the hemoglobin level, the protein in red blood cells that transports oxygen through your body, may also affect your results.
If you’re worried about your lung functioning and have recently been diagnosed with a lung disease, ask your physician if performing a diffusing capacity test may be helpful. Your physician will know if such a test is right for you, but don’t be afraid to ask questions.