What Is Lung Diffusion Testing?
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 are not 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.
What Is Lung Diffusion?
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) 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 is 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.
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. These diseases
- pulmonary hypertension (high blood pressure in
the arteries of the lungs)
- sarcoidosis (inflammation of the lungs)
If you show symptoms of lung disease, lung diffusion testing may
be used to analyze how your lungs are functioning. Also, if you are undergoing
treatment for lung disease, your doctor may order this test from time to time
to monitor the disease’s progress and how well treatment is working.
What to Expect During a Lung Diffusion Test
Before the Test
Your doctor may ask you to take certain steps to prepare for a
lung diffusion test, such as:
- avoiding use of a bronchodilator or other inhaled
medications prior to testing
- avoiding eating a large amount of food before
- avoiding smoking for several hours before the
In most cases, a lung
diffusion test involves the following steps:
- 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.
- You will take a breath of air. This air will contain
a tiny (and safe) amount of carbon monoxide.
- You will hold this air for a count of 10 or so.
- You will quickly exhale the air you are holding
in your lungs.
- This air will be collected and analyzed.
Potential Risks of a Lung Diffusion Test
Lung diffusion testing is a very safe and straightforward procedure.
A lung diffusion test doesn’t involve any serious risk. It’s a quick procedure
and shouldn’t cause most people any significant pain or discomfort.
Most likely, you won’t experience any negative side effects after
the test is complete.
Understanding Your Test Results
This test looks at how much of a certain gas you inhale and how
much is present in the air you exhale. Usually, the lab will use carbon
monoxide (or another “tracer” gas) to determine your lungs’ ability to diffuse
The lab will consider two things when determining the results of
the test: the amount of carbon monoxide that you originally inhaled and the
amount that you exhaled.
If there is far less carbon monoxide in the exhaled sample, it
indicates that a large amount of the gas was diffused from your lungs into your
blood. This is a sign of robust lung function. If the amount in the two samples
is similar, the diffusing capacity of your lungs is limited.
Your doctor will need to consider a number of factors to decide
whether your test results suggest problems with lung function. Factors include:
- whether or not you have emphysema
- whether you are a man or a woman
- your age
- how tall you are
- the amount of hemoglobin in your blood
Potential Causes of Abnormal Results
If your doctor determines that your lungs are not diffusing gas
at the level they should be, there may be a number of causes. These include:
- lung tissue loss or severe scarring
- foreign body obstructing an airway
- problems with arterial blood flow
- a blocked artery in the lung (pulmonary
- elevated blood pressure in the lung’s arteries
- hemorrhage in the lung
Additional Common Lung Function Tests
If your doctor suspects your lungs are not working properly, they
may order several tests in addition to the lung diffusion test. One such test is spirometry. This measures the amount
of air you intake and how fast you can exhale it. Another test, lung volume measurement, determines your
lung size and capacity.
The combined results of these tests can help your doctor figure
out what’s wrong and what steps can be taken to relieve your symptoms.