Plethysmography: Purpose, Procedure & Preparation
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Plethysmography

What Is Plethysmography?

Highlights

  1. Plethysmography uses blood pressure cuffs or other sensors to measure changes in volume in different parts of your body.
  2. Limb plethysmography is used to measure blood flow in your arms and legs. Lung plethysmography is used to measure the capacity of your lungs.
  3. Your doctor may order a plethysmography if you show signs of a blood clot in your legs or upper respiratory problems in your lungs.

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.

When Is Plethysmography Ordered?

purpose

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.

Procedure for a Plethysmography

process

Limb 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.

Lung Plethysmography

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 mouthpiece.

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.

How to Prepare for Your Plethysmography

Diagnosis

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 problems.

Interpreting the Tests

Results/Exams

Limb Plethysmography

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

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.

You Asked, We Answered

  • What are some possible causes of abnormal lung plethysmography results?
  • Lung plethysmography primarily measures the amount of air space in your lungs. If the amount of air space in your lungs is below normal, this may indicate several possible restrictive lung diseases. These rare diseases include sarcoidosis, idiopathic pulmonary fibrosis, and varieties of chronic interstitial lung diseases. Obesity can also cause breathing difficulties.

    - George Krucik, MD, MBA

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