How pulmonary function tests work

Jon Johnson 
by Deborah Weatherspoon, PhD, RN, CRNA
they test for Spirometry Lung volume tests Pulse oximetry test Lung diffusion
capacity Exercise test Results Preparation Risks Takeaway
Doctors carry out pulmonary
function tests to check how well a person’s lungs work and identify any issues.
The tests are noninvasive and provide measurements, such as lung capacity,
volume, and gas exchange.
These measurements may
indicate how well the person is breathing or how well the lungs can bring
oxygen to the rest of the body.
Every individual may require a
different type of test, and doctors may order one or more pulmonary function
tests (PFT), depending on the underlying issue.
conditions do pulmonary function tests identify?
Man breathing into peak flow
meter to test lung capacity as part of pulmonary function tests.
Pulmonary function tests can
help a doctor diagnose respiratory conditions, such as asthma or COPD.
There are many reasons for
pulmonary function tests.
Doctors may order PFTs to help
investigate or diagnose possible health conditions including:
chronic bronchitis
emphysema or COPD
lung cancer or pulmonary
lung fibrosis, where scar
tissue appears in the lung tissue
respiratory infections
sarcoidosis, which occurs when
inflammatory cells begin growing in the lungs
scleroderma, which causes the
connective tissues in the lungs to harden and become tight
Doctors may also order PFTs
for people who work in hazardous environments or breathe in very fine particles
in their workplace. This may include:
Doctors may also use PFTs to
monitor treatment or test the effectiveness of treatment for a chronic
condition, such as asthma, bronchitis, or COPD.
Doctors may also order PFTs to
check a person’s lung function before they have major surgery. This may be more
important in people who are at increased risk, such as those with heart or lung
problems and people who smoke.
Most PFTs are simple and
quick. The time and processes involved will vary depending on the type of test.
Spirometry is a test that
measures the amount of air a person breathes in and out.
Doctors may use this test when
they want to know the person’s lung size and the rate of airflow as they
During a spirometry test, the
person breathes through a tube attached to a computer. To ensure accurate
results, a doctor will fit a mouthpiece and a nose clip on the person to
prevent air from leaking.
The person then breathes
through their mouth as usual. After a few breaths, the doctor will ask the
person to breathe in deeply and then expel the air as fast as possible.
volume tests
Lung volume tests are the best
way to tell how much air a person’s lungs can hold.
The process is similar to
spirometry, where the person first breathes normally and then vigorously. The
person will sit in a small, sealed booth with clear walls for the test.
Doctors can very accurately
measure the amount of air the lungs displace by measuring the pressure in the
oximetry test
A pulse oximetry test on a
person’s finger measuring blood oxygen levels
A pulse oximetry test involves
clamping a device onto the body to measure blood oxygen levels.
A pulse oximetry test measures
the levels of oxygen in the blood, which can indicate how well the lungs
function. There is no breathing involved.
Doctors clamp a small device
to an area where the skin is thinner, such as an earlobe or finger. Tiny beams
of light then measure how much oxygen is in the blood.
This test can help diagnose
conditions, as well as determine how well certain treatments are working.
diffusion capacity
The purpose of a lung
diffusion capacity test is to see how well oxygen from the air a person
breathes gets into the blood.
For this test, a person sits
and breathes normally through a tube. There is no need for vigorous breathing
during this test. Doctors may also have the person breathe in various gases and
monitor how well the body uses or gets rid of these gases.
Doctors may also take a blood
sample to check the levels of hemoglobin in the blood.
When doctors are trying to
find the cause of specific symptoms, such as shortness of breath, they might
want to know how the lungs respond to exercise.
The test involves breathing
into a machine while walking on a treadmill or using a standing bike. The test
measures how a person responds to exercise at their own pace.
the results mean
average values change for each person.
Doctors will take the results
of the test and compare them to typical averages of people of a similar height,
age, and sex.
The American Thoracic Society
state that a person’s lungs grow until they reach their mid-20s when the lung
function slowly starts to decline. Height and sex are the other factors. Taller
people tend to have larger lungs and males tend to have larger lungs than
Values that are abnormal in
comparison to these other measurements may be a sign of an issue in the lungs.
Doctors may order one or more tests to help make a diagnosis depending on the
Individual results vary, and
doctors will explain the results of each test with each person.
The American Lung Association
note that it is possible for a person with healthy lungs to have abnormal
results. This is why doctors may run additional tests to confirm their findings
before moving forward with a diagnosis.
to prepare for a PFT
Man on treadmill with device
over mouth to measure lung capacity and breathing during exercise test with
woman on computer in background.
A doctor can provide specific
advice on how to prepare for PFT tests.
Preparation for a PFT may
differ between individuals, but there are some general guidelines.
Doctors frequently ask the
person to stop taking certain medications before the test to get an accurate
reading. The doctor will give each person specific instructions.
Doctors may also ask the
person to avoid certain foods or drinks that may make the results of a PFT
Strenuous exercise may also
open the airways and lead to an inaccurate reading. Avoid vigorous activity for
at least a couple of hours before the test.
Avoid eating or drinking too
much before the test. A full stomach may leave less room for the lungs to
expand, which could affect the results of a lung capacity test.
Doctors may also ask the
person to refrain from smoking or drinking alcohol before the test.
People should avoid wearing
tight clothing that may prevent the lungs from inhaling fully.
Anyone who is taking an
exercise test should wear loose fitting, comfortable clothing to take the test.
of the tests
While the tests are generally
safe and noninvasive, there are some risks.
Many tests require the person
to breathe in and out vigorously. This may make some people feel dizzy, and
there is a risk that they may faint. Anyone feeling dizzy or lightheaded during
the test should tell the person administering the test.
The tests may trigger asthma
attacks in some people, especially if they do not take their medication in
preparation for the test.
There is minimal risk of germs
spreading from people using the same lung function equipment. Technicians
change the mouthpieces and other equipment after each use, and the machines
have filters to help kill germs.
The National Heart, Lung, and
Blood Institute note that in tests that require doctors to take blood, some
people may experience bleeding or infection in the area.
PFTs are noninvasive tools
that doctors use to check how well the lungs perform their functions. They are
generally safe and are highly useful for diagnosing and monitoring certain
conditions in the lungs and airways.
People with specific
conditions may have difficulty carrying out some of these tests. Always communicate
with a doctor, ask questions, voice any concerns, and work together to find a
Kayode Ojo
Kayode Emmanuel Ojo is the Co-Founder and Managing Director at SHEFFA Limited. He is presently studying Computer Science at the National Open University, Victoria Island, Lagos.