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What is PAH?

PAH is the medical abbreviation for pulmonary arterial hypertension. PAH causes the millions of tiny blood vessels in your lungs to thicken and narrow. This makes it difficult for blood to flow from your heart through your lungs, creating high blood pressure in the lung vessels. As blood flow through the lungs is reduced, your lungs don’t receive enough oxygen. The pressure in the lungs causes the right side of the heart to work harder than normal.

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PH, which stands for pulmonary hypertension, is a more general term used to describe any condition in which the blood pressure of the vessels in your lungs is too high, such as chronic lung disease, heart disease or chronic blood clots. Pulmonary arterial hypertension (PAH) is a rare type of PH that causes the pressure in the pulmonary arteries to rise.

PAH is a serious disease that gets worse over time. Whether you're undiagnosed or already on treatment, it's important to talk with your doctor about the symptoms you're experiencing—and the activities that trigger them—so that he/she can assess your condition correctly and treat it the best way for you.

Signs and symptoms of PAH include dizziness, shortness of breath, feeling tired, fainting and swollen ankles or legs.

PAH Symptoms

Signs and symptoms of PAH include:

  • Feeling dizzy
  • Shortness of breath
  • Feeling tired
  • Fainting
  • Swollen ankles or legs

Early on, you may notice these symptoms of PAH during physical activity. As the disease progresses, symptoms can happen even at rest.

Because PAH gets worse over time, it’s important to have an honest conversation with your doctor about how you’re really feeling, regardless of your test results (which only tell part of the story). It may be necessary to adjust your dose of medicine(s) or add treatment to help control PAH symptoms and keep your PAH from getting worse.

Let's take a look at how PAH impacts your body

Sometimes, it helps to actually see what’s happening in the body to understand how PAH causes the symptoms you may be experiencing.

Watch this video that shows how PAH affects the vessels in your lungs and how this impacts your heart.

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PAH Diagnosis

Diagnosing PAH can be hard because it is rare and has a lot of the same symptoms as more common diseases or conditions. While some cases are passed down through family, many people with PAH don't know the cause of their disease. If you have symptoms of PAH, your doctor may conduct specific tests to assess for PAH, including:

Chest x-rays

show whether the arteries in your lungs and right ventricle are enlarged

Blood tests

rule out any other diseases that may be causing your symptoms

Ventilation/Perfusion scans

or V/Q lung scans, measure your breathing and the circulation in your lungs


allow your doctor to see your heart as it pumps

Pulmonary function tests

or PFTs, measure your lung function

Right-Heart Catheterization (RHC)

While the tests help your doctor better understand your condition, the only way to actually confirm that you have PAH is for your doctor to perform a right-heart catheterization (RHC) to measure the pressures in your heart and the arteries in your lungs. A RHC also measures how much blood your heart pumps through your lungs and the resistance in the blood vessels in your lungs. It is not only an important measure of how severe your PAH is, but also helps guide treatment decisions, and helps identify other issues that may be adding to your symptoms.

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Other Considerations

A doctor may also assess your 6-minute walk distance, or 6MWD, which tracks how far you can walk on a flat surface in 6 minutes. This is one of the most common tests to determine your ability to exercise. It is an important test for people with PAH and is often conducted on a regular basis.

What's your functional class?

Another measure of PAH severity is determined by your functional class (FC). Your healthcare provider will determine your FC based on the information you share about your daily activities – specifically, those activities that cause you to experience symptoms of PAH, such as shortness of breath, fatigue or fainting. There are 4 functional classes, ranging from least severe (Class I) to most severe (Class IV).

WHO functional class system for PAH classification
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Managing Your Pah

Want to learn how you can do more about your PAH?

Manage Your PAH

You can accept feeling okay, or you can ask about feeling better. Ask your doctor to help you feel better and do more.

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