Pulmonary Function
Testing
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What is the
test?
Your doctor can get a great deal of information
about your lungs and lung function by doing a
series of tests called pulmonary function testing.
These tests can tell your doctor what quantity
of air you breathe with each breath, how efficiently
you move air in and out of your lungs, and how
well your lungs are delivering oxygen to your
bloodstream.
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How
do I prepare for the test?
No preparation is necessary.
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What
happens when the test is performed?
This testing is done in a special laboratory.
During the test, you are instructed to breathe
in and out through a tube that is connected to
various machines.
A test called spirometry measures how forcefully
you are able to inhale and exhale when you are
trying to take as large a breath as possible.
The lab technicians encourage you to give this
test your best effort, because you can make the
test result abnormal just by not trying hard.
A separate test to measure your lung volume
(size) is done in one of two ways. One way is
to have you inhale a small carefully measured
amount of a specific gas (such as helium) that
is not absorbed into your bloodstream. This gas
mixes with the air in your lungs before you breathe
it out again. The air and helium that you breathe
out is tested to see how much the helium was
diluted by the air in your lungs, and a calculation
can reveal how much air your lungs were holding
in the first place.
The other way to measure lung volume is with
a test called plethysmography. In this test,
you sit inside an airtight cubicle that looks
like a phone booth, and you breathe in and out
through a pipe in the wall. The air pressure
inside the box changes with your breathing because
your chest expands and contracts while you breathe.
This pressure change can be measured and used
to calculate the amount of air you are breathing.
Your lungs' efficiency at delivering oxygen
and other gases to your bloodstream is known
as your diffusion capacity. To measure this,
you breathe in a small quantity of carbon monoxide
(too small a quantity to do you any harm), and
the amount you breathe out is measured. Your
ability to absorb carbon monoxide into the blood
is representative of your ability to absorb other
gases, such as oxygen.
Some patients have variations of these tests-for
example, with inhaler medicines given partway
through a test to see if the results improve,
or with a test being done during exercise. Some
patients also have their oxygen level measured
in the pulmonary function lab (see "Oxygen saturation
test,"
page 29).
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What
risks are there from the test?
There are no risks.
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Must
I do anything special after the test is over?
No.
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How
long is it before the result of the test is
known?
Your doctor will receive a copy of your test
results within a few days and can review them
with you then.
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