The World Health Organization (WHO) classifies the five main types of pulmonary hypertension (PH) by underlying cause. Pulmonary hypertension refers to high blood pressure in the lungs for any reason. For example, you may hear the terms “pulmonary arterial hypertension” (or PAH), which is high blood pressure in the lungs specifically caused by narrowed arteries. It’s important to understand that pulmonary hypertension is the collective term, and PAH is a subtype of PH.

Your doctor will evaluate the type and class of your PH during the process of diagnosis. Knowing the type and class of PH you have helps doctors decide which PH treatments will be most effective.

Read more about causes and risk factors for pulmonary hypertension, as well as symptoms of the condition.

Normal Heart and Lung Function

It helps to know a little about the anatomy of the heart and lungs and how the two work together.

There are four heart chambers — two atria (left and right) on top and two ventricles (left and right) below them. The right-side chambers of the heart circulate blood to the lungs, while the left-side chambers of the heart receive blood from the lungs and circulate blood through the body. The right atrium receives oxygen-depleted blood from the body and moves it into the right ventricle, which pumps it into the lungs through the left and right pulmonary arteries. The deoxygenated blood moves through progressively smaller arteries into the capillaries (tiny blood vessels) of the lung, where it picks up a fresh oxygen supply. Now rich in oxygen, blood returns to the left atrium through the pulmonary veins. The left atrium receives oxygenated blood from the lungs and moves it into the left ventricle — the largest and most powerful chamber of the heart — which pumps the blood around the body.

Additionally, there are four heart valves — mitral, aortic, tricuspid, and pulmonary — that control the flow between each chamber of the heart and through the lungs. The valves open to allow forward flow and snap shut to prevent backward flow.

Pulmonary Hypertension Types

The WHO classifies PH into five main groups based on the cause of the condition.

Group 1: Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is caused by narrowing of the pulmonary arteries, usually due to inflammation and thickening of the muscular layer of the arterial wall. There are several subcategories of PAH:

• Idiopathic PAH has no known cause.
• Heritable PAH is inherited from a parent.
• Drug- or toxin-induced PAH is caused by exposure to a medication, illegal stimulants, some types of weight loss drugs, or toxins.
• Associated PAH is caused by another disease.

Diseases that can cause associated PAH include:

• Chronic obstructive pulmonary disease (COPD)
• Congenital (present at birth) heart problems
• Eisenmenger syndrome
• HIV infection
• Liver disease
• Lupus
• Sarcoidosis
• Schistosomiasis
• Scleroderma
• Sickle cell disease
• Sleep apnea

Group 2: Pulmonary Hypertension Due to Left Heart Disease

With group 2 pulmonary hypertension, PH is caused by left heart disease. When disease damages the left ventricle, it can no longer pump blood effectively around the body. Deoxygenated blood backs up, causing high blood pressure in the pulmonary arteries. This is also known as congestive heart failure.

Other types of heart disease that may cause PH include:

• Mitral valve problems
• Aortic valve problems
• Coronary artery disease (CAD)
• Congenital heart defects
• Chronic high blood pressure throughout the body

Treating the underlying heart disease will help alleviate PH symptoms.

Group 3: Pulmonary Hypertension Due to Lung Disease

Group 3 pulmonary hypertension is caused by chronic hypoxia — low oxygen levels — due to lung disease or sleep-related breathing disorders. Conditions that can cause group 3 PH include COPD, interstitial lung disease, and sleep apnea. For some people, group 3 PH can be caused by low oxygen from living at high altitudes. Group 3 PH can be treated with supportive oxygen therapy. For severe PH, a lung transplant might help.

Group 2 and 3 PH are far more common than group 1 PAH. In other words, most pulmonary hypertension is caused by heart and lung diseases.

Group 4: Pulmonary Hypertension Due to Blood Clots in the Lungs

Also known as chronic thromboembolic pulmonary hypertension (CTEPH), group 4 PH is caused by blood clots that have become lodged in the pulmonary arteries. The clots raise the blood pressure in the arteries, leading to PH symptoms. CTEPH is the only type of PH that can potentially be cured — with surgery, for some individuals. However, not everyone with CTEPH is a good candidate for surgery. Because group 4 PH is caused by blood clots, treatment requires taking blood thinners.

Group 5: Pulmonary Hypertension Due to Unknown Causes

Cases of PH in group 5 are caused by other conditions or by multiple health factors. Any disease that interferes with the circulation of blood through the lungs can potentially cause pulmonary hypertension. Treating the underlying condition will help PH symptoms.

Conditions that can cause group 5 pulmonary hypertension include:

• Chronic hemolytic anemia
• Chronic kidney failure
• Fibrosing mediastinitis
• Gaucher’s disease
• Glycogen storage disease
• Late side effects of splenectomy
• Leukemia
• Polycythemia vera
• Sarcoidosis
• Thrombocythemia
• Thyroid disease
• Tumors that compress the pulmonary arteries

Talk With Others Who Understand

On myPHteam, the social network for people with pulmonary hypertension and their loved ones, more than 50,000 members come together to ask questions, give advice, and share their stories with others who understand life with pulmonary hypertension.

Have you been diagnosed with PH? What type do you have? Share your experience in the comments below, or start a conversation by posting on your Activities page.