Plethysmography measures changes in volume in different areas of
your body. It measures these changes with blood pressure cuffs or other sensors.
These are attached to a machine called a plethysmograph.
Plethysmography is especially effective in detecting changes
caused by blood flow. It can help your doctor determine if you have a blood
clot in your arm or leg. It can also help your doctor calculate the volume of
air your lungs can hold.
Is Plethysmography Ordered?
Your doctor may order a limb plethysmography if you show signs of
blood clots in your legs. Symptoms of blood clots include redness, warmth,
swelling, and tenderness. Plethysmography is not as accurate as an arteriogram,
which is more commonly used to identify blood clots. But it’s less invasive and
less expensive. These factors make it more appealing to many individuals.
You doctor may order a lung plethysmography if you have symptoms
of upper respiratory problems. These symptoms include pain or discomfort while
breathing and shortness of breath. Your doctor can’t diagnose the underlying
cause of your problem from plethysmography alone. However, an abnormal test
result can confirm if something is preventing your lungs from holding as much
air as they should.
for a Plethysmography
A limb plethysmography can be performed in a doctor’s office or
hospital. If you’re wearing pants or a long-sleeved shirt, your doctor will ask
you to undress and put on a hospital gown. They’ll ask you to keep one leg and
one arm bare. You will recline in a comfortable position on an examination
table, cot, or gurney.
Your doctor will then place blood pressure cuffs on your leg and
arm. They’ll be most interested in checking your systolic blood pressure. That’s
the pressure of blood in your arm and leg when your heart contracts. You may
feel a little uncomfortable when the blood pressure cuffs tighten around your
arm and leg, but you won’t feel any real pain. The test usually lasts about 20
to 30 minutes. During this time, you’ll be asked to move as little as possible.
Limb plethysmography is not associated with any risks or side
effects. Unless your doctor tells you otherwise, you can resume your regular
schedule immediately after the test.
A lung plethysmography can be performed in a specialist’s office
or in a hospital. You will sit in a small, airtight room. Your doctor will use
clips to close off your nostrils. Then they’ll ask you to breathe against a
Some people report becoming short of breath or lightheaded. Let
your doctor know if you experience these symptoms during the test.
Unless your doctor tells you otherwise, you can resume your
regular activities immediately after the test.
to Prepare for Your Plethysmography
There are no special requirements to prepare for a limb plethysmography.
If you’re having a lung plethysmography, you should avoid smoking
and doing aerobic exercise for eight hours before the test. You should also eat
lightly because heavy meals can affect your ability to breathe deeply. It’s
best to wear loose, comfortable clothing.
The test requires sitting in a small space, so it can be hard for
people who have claustrophobia, or a fear of small spaces. Let your doctor know
if you think this may be a problem for you. It’s also important to tell your
doctor if you’re taking any medications, especially medications for breathing
Normally, the systolic blood pressure in your arm and leg are
similar. The ankle-brachial index (ABI) is a measurement used to check for
potential problems. To calculate your ABI, divide the highest systolic blood
pressure reading from your leg by the highest reading from your arm.
A normal ABI falls between 0.90 and 1.30, according to the National
Heart, Lung, and Blood Institute. If your ABI falls outside this range, you
may have a narrow or blocked artery. Your doctor can order additional tests to
determine the exact nature of the problem.
Lung plethysmography measures how much air you can hold in your
lungs. The normal range depends on your age, gender, body size, and level of fitness.
This test is a starting point for your diagnosis. An abnormal
result confirms that there’s a problem with your lung capacity. But it doesn’t
tell your doctor what that problem might be. Your doctor would have to do
additional tests to discover why your results were abnormal. Possibilities include
a breakdown of lung tissue and problems with the muscles around your chest wall.
They also include problems with your lungs’ ability to contract and expand.