Your body craves oxygen. Every organ — from your brain to the muscles in your toes — needs oxygen to help you think, move, and go about your day. To deliver this oxygen, your body uses an impressive network of blood vessels, including veins and arteries. One especially important vessel is the pulmonary artery, which carries blood from the heart to the lungs. In the lungs, the blood picks up oxygen before circulating to the rest of the body.

Sometimes, this system doesn’t work the way it should. When pressure builds in the blood vessels in the lungs, it can lead to pulmonary hypertension (PH) — a condition that makes it harder for the heart to pump blood through the lungs. One specific type of PH is pulmonary arterial hypertension (PAH), which affects the small arteries in the lungs.

Here are five key facts about the pulmonary artery — how it works and what role it plays in PH and PAH.

1. Pulmonary Arteries Are the Only Arteries That Carry Oxygen-Poor Blood

To keep your tissues working well, your body uses a network of long tubes called arteries to carry blood — filled with oxygen and nutrients — to every part of your body. Once the blood reaches your tissues, they absorb the oxygen they need to function.

Most arteries deliver oxygen-rich blood. But pulmonary arteries are different. They’re the only arteries in the body that carry deoxygenated (oxygen-poor) blood. These arteries carry blood from your heart to your lungs, where the blood picks up oxygen. That oxygenated (oxygen-rich) blood is then sent back to your heart and pumped out to the rest of your body.

The pulmonary arteries are part of the pulmonary circuit — the system that moves blood between your heart and lungs to refill blood with oxygen. This system begins with a large blood vessel called the pulmonary trunk (also known as the main pulmonary artery), which exits the right side of the heart. It splits into two arteries: one that goes to your left lung and one to your right lung. These arteries then branch into smaller vessels throughout each lung.

Blood that’s low in oxygen travels from the right side of your heart through your pulmonary arteries to your lungs. Once there, it picks up oxygen. Then, pulmonary veins carry the oxygen-rich blood back to your left heart chambers to be pumped back out to different parts of your body.

2. Healthy Pulmonary Arteries Don’t Require a Lot of Pressure To Circulate Blood

When the pulmonary circuit is healthy, the average blood pressure within the pulmonary arteries should be fairly low — about 11 to 20 millimeters of mercury (mm Hg). That’s much lower than systemic blood pressure (the pressure in the rest of your body’s arteries), which normally peaks around 120 mm Hg.

Why the difference? Blood in the pulmonary circuit doesn’t have far to travel — just from the heart to the lungs and back. Because of that short distance, the heart doesn’t need to push very hard to send blood to the lungs. This makes the pulmonary arteries a low-pressure system under normal conditions.

But when pressure in the pulmonary arteries rises, it becomes harder for your heart — especially the right side of your heart — to pump blood effectively. Over time, this extra effort can strain or damage the heart muscle.

This condition is called pulmonary hypertension. If PH becomes severe or goes untreated, it can progress and lead to right-sided heart failure — when the right side of the heart becomes too weak to keep up.

3. Increased Pressure in the Pulmonary Arteries Has Many Potential Causes

What causes pressure to rise in the pulmonary arteries? There are many possible reasons — most linked to other medical conditions. Some common causes of pulmonary hypertension include:

• Narrowing or blockage in the pulmonary arteries
• Chronic lung conditions such as chronic obstructive pulmonary disease (COPD) or emphysema
• Congenital heart disease (a heart problem present from birth)
• Connective tissue diseases, such as scleroderma (an autoimmune disease that affects skin and internal organs)
• Heart failure on the left side of the heart
• Liver disease

The underlying cause helps determine which of the five types of pulmonary hypertension someone may have. For example, if the PH is caused by narrowed or blocked arteries in the lungs, the diagnosis may be pulmonary arterial hypertension.

Several myPHteam members have shared what they believe caused their pulmonary hypertension. One member wrote, “I’ve had clots in my lungs twice.”

This member was describing a pulmonary embolism — a condition where a blood clot travels from another part of the body (often the legs), through the heart, and into the lungs. These clots can get stuck in a vein and cause a blockage in blood flow, causing pressure to build in the pulmonary arteries. It’s similar to a clogged pipe causing water to back up in a sink. Left untreated, the blockage raises pulmonary artery blood pressure and can lead to pulmonary hypertension.

Genetics can also play a role. Some people inherit mutations (gene changes) linked to PH. Having a family history of PH may mean you have heritable pulmonary arterial hypertension. When no clear cause can be found, the condition is called idiopathic pulmonary arterial hypertension.

4. Many Tests Can Help Diagnose Pulmonary Hypertension

No matter the cause, all types of pulmonary hypertension involve increased pressure in the pulmonary arteries — the blood vessels that carry blood from the heart to the lungs. Common signs and symptoms of PH include shortness of breath, chest pain, and fatigue. If a healthcare provider suspects PH, they may use several tests to measure pulmonary artery pressure and confirm the diagnosis.

Pulmonary hypertension is caused by increased pressure in the pulmonary arteries.

The most accurate way to diagnose PH is through a test called right heart catheterization. In this procedure, a doctor threads a thin tube, called a catheter, through a blood vessel and into the right side of your heart. This allows them to measure pulmonary artery pressure directly. The catheter can also help detect blood clots or narrowed vessels that may be contributing to PH.

Other helpful tests include:

• Echocardiogram — This is a noninvasive ultrasound that creates moving pictures of your heart. It can help estimate pressure in your pulmonary arteries and assess how well your heart is pumping.
• Chest X-ray or cardiac MRI — These imaging tests give a closer look at your heart and lungs to check for changes linked to PH.
• Blood tests — These can show how well your lungs are delivering oxygen, detect signs of inflammation or heart strain, and screen for blood clots.

5. PH Treatments Can Help Improve Blood Flow Through the Pulmonary Arteries

Although there’s currently no cure for pulmonary hypertension, a variety of treatments can help improve blood flow through the pulmonary arteries, reduce symptoms, and support a better quality of life.

A range of medications focuses on lowering the pressure in the pulmonary arteries or addressing its cause. These include:

• Anticoagulants (blood thinners) — Help prevent blood clots that can block blood flow and raise pressure in the lungs
• Vasodilators, such as calcium channel blockers — Help relax and open blood vessels to reduce pressure
• Diuretics (water pills) — Help the body get rid of extra fluid that puts strain on the heart and lungs

Pulmonary hypertension treatments aim to reduce pressure and improve blood flow in the pulmonary arteries.

Other classes of medications can help manage PH by targeting different pathways in the body:

• Endothelin receptor antagonists
• Phosphodiesterase inhibitors (PDE 5 inhibitors)
• Prostacyclin analog drugs
• Selective IP receptor drugs
• Activin-signaling inhibitors

If medications aren’t enough, procedures or surgery may be recommended for more serious cases:

• Balloon pulmonary angioplasty — A minimally invasive procedure to open narrowed pulmonary arteries
• Lung transplant — An option for people with severe PH who don’t respond to other treatments

It’s also important to support your overall well-being by getting as much physical activity as is appropriate for your health and eating a healthy diet. Talk with your doctor about what kind of activity and food will be best for you in combination with your pulmonary hypertension treatment.

Talk With Others Who Understand

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.

Do you have more questions about how pulmonary arteries function? How was your diagnostic journey with pulmonary hypertension? Share your knowledge and questions in the comments below, or start a conversation by posting on your Activities page.