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If you’ve been diagnosed with pulmonary arterial hypertension (PAH) or another type of pulmonary hypertension (PH), you’ve probably had more tests than you can count. But what are they measuring, and why does it matter? This article breaks down the pressure readings doctors use to check how your heart and lungs are working and how those results can guide your care.
One of the most important readings is pulmonary arterial pressure (PAP). It helps your healthcare providers figure out what type of PH you have and how advanced it is. This information can help you and your doctor choose the treatment plan that’s right for you.
Here are eight facts about PAP, including what it means and how it’s measured.
PAP measures the force of blood pushing on the walls of the arteries in your lungs. If you have PAH, your PAP may be higher than normal. This is because, in PAH, the small arteries in the lungs are thicker and narrower. These abnormalities affect pulmonary circulation and make it more difficult for blood to pass through the arteries.
When your blood has a harder time passing through the small arteries in your lungs, it increases the force or pressure that blood puts on the walls of these blood vessels. Because your heart and lungs are connected, the right side of your heart has to work harder to push your blood through these arteries.
Talk to your healthcare provider about what your results mean. As a myPHteam member shared, “My pressure was 50, and I was told I have severe pulmonary arterial hypertension.”
Your healthcare provider may order a test to measure your PAP to help diagnose or monitor PAH.
Two procedures — right heart catheterization and transthoracic echocardiography (TTE) — can measure your PAP. These procedures help your provider understand how your blood flows between your heart and lungs (also called hemodynamics).
Healthcare providers can measure PAP during a right heart catheterization. This procedure measures the pressure inside your pulmonary arteries and is the most accurate way to diagnose PH. Most people with PH will undergo this procedure at least once.
Right heart catheterization is usually performed by a cardiologist (a doctor who specializes in treating heart conditions). During this procedure, the doctor will guide a thin, flexible tube (called a catheter) from a large blood vessel in your neck or groin to the right side of your heart. When the catheter is in your heart, your doctor can measure the blood pressure in your right atrium, right ventricle, and pulmonary artery.
Right heart catheterization gives doctors information about your blood flow and pressure. This cardiovascular information can be used to learn which type of PH you have and how severe it is.
Some measurements taken during a right heart catheterization include:
Your mPAP is a measure of the pressure in your pulmonary artery taken during a right heart catheterization. It’s measured in millimeters of mercury (mm Hg), a measure of pressure. In someone without PH, mPAP is usually between 8 mm Hg and 20 mm Hg.
Another way to measure PAP is with TTE. This procedure uses sound waves to create an image of your heart.
Unlike a right heart catheterization, TTE gives only an estimate of pulmonary arterial pressure. Rather than measuring the mPAP, echocardiography estimates the systolic pressure — the force in the pulmonary arteries when the heart beats — known as systolic pulmonary arterial pressure (sPAP).
When pressure builds up in the pulmonary arteries, the right side of the heart has to work harder to push blood through them. This extra pressure can cause some blood to leak backward through a part of the heart called the tricuspid valve, sending it back into the right atrium.
Doctors estimate sPAP by measuring how fast this backward flow moves. The faster it moves, the higher the pressure is likely to be. PH can also make the right heart chambers look larger and thicker than normal on an echocardiogram (heart ultrasound).
If you have an echocardiography test, you may need a right heart catheterization later. As a member of myPHteam shared, “I saw the pulmonologist, and he suggested I consult with a cardiologist and have this right-side heart catheterization, which he says will give a more accurate reading. An echo is an estimated reading.”
PCWP estimates the pressure in the small pulmonary vessels, which reflects the pressure in your heart’s left atrium. It may also be referred to as pulmonary arterial wedge pressure.
A normal PCWP is considered 15 mm Hg or less. PCWP may be normal in some people with a type of group 1 PH called precapillary PH. However, PCWP may be higher in people with PH due to left heart disease.
Your healthcare provider can use PCWP to calculate other measurements to help classify and monitor your PH, including pulmonary vascular resistance (PVR).
PVR is a calculation of the resistance your blood faces when flowing from the veins in your lungs to your heart. Your healthcare provider can calculate PVR using your mPAP, PCWP, and cardiac output from a right heart catheterization.
PVR uses a unique measurement system called Wood units, named after the man who first described it, Paul Wood. A normal PVR is 0.3 to 2 Wood units. People with PH have a PVR higher than 2 Wood units.
Measurements such as mPAP, PCWP, and PVR are important factors your healthcare provider will consider when suggesting your PH treatment plan.
These measurements can help define the type of PH and how severe it is. They can help your doctor predict if you might be at risk of serious health problems like heart failure in the next year. This information is used to determine if you may need more advanced interventions like lung transplantation.
Your mPAP can be used to predict how certain treatments will work. In some cases, during a right heart catheterization, your cardiology provider may perform a vasoreactivity test (also called a vasodilator test). The purpose of this test is to see if calcium channel blockers will work for you to help lower your blood pressure. During this test, you’ll inhale a vasodilator — a drug that causes blood vessels to expand — while your doctor looks at your mPAP measurement. If your mPAP decreases by at least 10 mm Hg to reach a value below 40 mm Hg, calcium channel blockers may be a good treatment option for you.
PVR can also be used to monitor how well your treatment is working at follow-up appointments. In general, a reduction in your PVR shows that your treatment is working. Worsening PVR or no improvement may mean you need a new treatment. You may also see PVR measured in clinical trials for new PH treatments.
After a right heart catheterization, a myPHteam member shared, “I was told that I was no longer severe but moderate. I am very active. I use four different medications.”
When treating your PH or PAH, doctors will use measurements of PAP in addition to other factors about your condition. Your symptoms and how they affect your daily life and exercise can change your treatment. All of these factors help your healthcare provider better understand your PH and determine the best treatment plan for you.
On myPHteam, the social network for people with pulmonary hypertension and their loved ones, more than 57,000 members come together to ask questions, give advice, and share their stories with others who understand life with pulmonary hypertension.
Have you had a right heart catheterization or transthoracic echocardiography? How were your mPAP and PCWP measurements affected by your treatment? Share your experience in the comments below, or start a conversation by posting on your Activities page.
I Have COPD. I've Been Told For Years That I Also Have Pulmonary Hypertension. As Time Goes On, Is The PH Taking Over?
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Find a cardio specialist in PAH and PH. They should explain every step. Are you on O2?