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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’s being measured, 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.
To start, PH refers to high blood pressure in the arteries in your lungs, and PAH is one type of PH that affects the smaller arteries. Doctors use pressure readings to help determine which type of PH you have.
One of the most important readings is pulmonary arterial pressure (PAP), which 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 against the walls of the arteries in the lungs. If you have PAH, your PAP may be higher than normal. This happens because in PAH, the small arteries in the lungs become thicker and narrower, which affects blood flow and makes it harder for blood to pass through the arteries.
The reduced blood flow raises the pressure inside these arteries. Because your heart and lungs work closely together, the right side of your heart has to work harder to push blood through the narrowed arteries.
Talk with your healthcare provider about what your results mean. “My pressure was 50, and I was told I have severe pulmonary arterial hypertension,” one myPHteam member shared.
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 provide more information about PAP. Right heart catheterization directly measures PAP, while TTE provides an estimate. These procedures help your provider understand how your blood flows between your heart and lungs (also called hemodynamics).
Healthcare providers measure PAP during a right heart catheterization, which is the most accurate test for diagnosing 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 guides a catheter (a thin, flexible tube) through a large blood vessel in your neck or groin to the right side of your heart. Once the catheter is in place, the doctor can measure blood pressure in your right atrium, right ventricle, and pulmonary artery.
Right heart catheterization gives doctors information about blood flow and pressure. This cardiovascular information can be used to learn which type of PH you have and how severe it is. Measurements taken during a right heart catheterization include:
Your mPAP is the pressure in your pulmonary artery measured during a right heart catheterization. It’s measured in millimeters of mercury (mm Hg). In someone without PH, mPAP is usually between 8 and 20 mm Hg. PH occurs when mPAP is greater than 20 mm Hg at rest.
Another way to estimate PAP is with TTE. This procedure uses sound waves to create an image of the heart.
Unlike a right heart catheterization, TTE provides only an estimate of PAP. Rather than directly measuring mPAP, echocardiography estimates systolic PAP (sPAP), which reflects pressure in the pulmonary arteries during a heartbeat.
When pressure builds up in the pulmonary arteries, the right side of the heart has to work harder to push blood through. This increased strain can cause some blood to leak backward through the tricuspid valve, flowing back into the right atrium.
Doctors estimate sPAP by measuring how fast this backward flow travels. The faster it flows, the higher the pressure is likely to be. PH can also make the right heart chambers appear 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-sided heart catheterization, which he says will give a more accurate reading. An echo is an estimated reading.”
PCWP estimates pressure in the pulmonary circulation and reflects pressure in the heart’s left atrium. It may also be called pulmonary arterial wedge pressure.
A normal PCWP is 15 mm Hg or less. PCWP may be normal in people with a type of group 1 PH called precapillary PH. However, PCWP is often higher in people with PH due to left heart disease.
Healthcare providers can use PCWP to calculate other measurements that help classify and monitor PH, including pulmonary vascular resistance (PVR).
PVR describes how much resistance blood faces as it flows through the blood vessels in the lungs. A higher PVR means that pulmonary vessels are stiffer and narrower. Healthcare providers calculate PVR using mPAP, PCWP, and cardiac output from a right heart catheterization.
PVR is reported using a unit of measurement called Wood units, named after Paul Wood, the physician who first described it. A normal PVR is about 0.3 to 2 Wood units. Precapillary PH, including PAH, is defined by a PVR greater than 2 Wood units with a wedge pressure of 15 mm Hg or less. Postcapillary PH, which is caused by left heart disease, may have a PVR of 2 Wood units or less or, if there’s extra vessel disease, more than 2 Wood units.
Measurements such as mPAP, PCWP, and PVR are important factors your healthcare provider will consider when developing your PH treatment plan. These measurements help define the type of PH and how severe it is. They help estimate the risk of complications, such as heart failure, in the next year and determine if you may need more advanced interventions like lung transplantation.
Your mPAP can be used to predict how certain treatments will work. During a right heart catheterization, your cardiology provider might perform a vasoreactivity test (also called a vasodilator test) to see if calcium channel blockers will work to 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. Doctors consider the test positive only if mPAP drops by at least 10 mm Hg to 40 mm Hg or less, with unchanged or increased cardiac output. If that happens, calcium channel blockers may be a good option for some people with PAH.
PVR can also be used to monitor your treatment’s effectiveness. In general, a reduction in 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 related to your health. Your symptoms and how they affect your daily activities and exercise can influence your treatment plan.
On myPHteam, people share their experiences with pulmonary hypertension, get advice, and find support from others who understand.
Have you had a right heart catheterization or transthoracic echocardiography? How were your mPAP and PCWP measurements affected by your treatment? Let others know in the comments below.
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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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