Pulmonary hypertension is caused by changes to the pulmonary arteries, the blood vessels that carry blood from the heart to the lungs.

There are 5 main types of pulmonary hypertension.

Pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is caused by changes in the smaller branches of the pulmonary arteries.

The walls of the arteries become thick and stiff, narrowing the space for blood to pass through and increasing blood pressure.

PAH can be associated with other conditions, including:

• connective tissue diseases – such as scleroderma, a condition that causes thickened areas of skin and problems with blood vessels
• congenital heart problems – such as a hole in the heart
• portal hypertension – abnormally high blood pressure inside the liver, which causes veins to become swollen
• HIV
• certain medicines or drugs
• thyroid gland disorder
• sickle cell disease and related conditions
• glycogen storage disorders – glycogen is a carbohydrate that produces short-term energy
• pulmonary veno-occlusive disease – a rare condition that causes high blood pressure in the lungs
• pulmonary capillary hemangiomatosis – another rare condition where tiny blood vessels (capillaries) grow within the lungs, causing blockages

A small number of people develop PAH without having any other medical condition. This is called idiopathic PAH. In very rare cases, PAH can be inherited. 

Persistent pulmonary hypertension of the newborn

In rare cases, newborn babies can have high pressure inside their blood vessels, which means their heart cannot pump enough oxygenated blood around their body. This is known as persistent pulmonary hypertension of the newborn (PPHN).

Treatment in an intensive care unit may be needed if simple measures such as keeping the baby warm and giving oxygen does not increase oxygen levels to normal.

The Great Ormond Street Hospital for Children website has more information about persistent pulmonary hypertension of the newborn.

Pulmonary hypertension linked to left heart disease

If there are problems with the left side of the heart, the right side has to work harder to pump blood through the lungs. This increases blood pressure in the pulmonary arteries.

Problems with the left side of the heart are thought to be one of the most common causes of pulmonary hypertension. These include mitral valve problems, left ventricle problems and aortic valve conditions.

Pulmonary hypertension linked with lung disease or lack of oxygen 

Pulmonary hypertension is also sometimes linked with lung diseases or lack of oxygen (hypoxia), including:

• chronic obstructive pulmonary disease (COPD) – a number of lung conditions that affect breathing
• interstitial lung disease – a group of lung disorders that cause scarring of the lung tissue, which makes it difficult to get enough oxygen into your body
• conditions that affect breathing while you're in a deep sleep – such as obstructive sleep apnoea

Low levels of oxygen in the blood make the pulmonary arteries narrow. This squeezes the blood into a smaller space, which increases blood pressure, causing pulmonary hypertension.

Pulmonary hypertension caused by blood clots 

Pulmonary hypertension can sometimes be caused by scars from previous blood clots that narrow or block the pulmonary arteries. This is called chronic thromboembolic pulmonary hypertension.

A blood clot that blocks one of the blood vessels that supply your lungs is called a pulmonary embolism.

Other causes of pulmonary hypertension 

Other, less common, causes of pulmonary hypertension include: 

• sarcoidosis – a condition that causes inflammation of different organs, including the lungs and lymph nodes
• histiocytosis X – a rare condition that causes scarring (granulomas) and air-filled cysts, mainly in the lungs
• compression of the blood vessels in the lungs – for example, as the result of a tumour

Read about how pulmonary hypertension is diagnosed.

Pulmonary hypertension can be difficult to diagnose because the symptoms are similar to those of other heart or lung conditions.

This means there can sometimes be a delay before a correct diagnosis is made.

See a GP if you have symptoms of pulmonary hypertension, such as breathlessness and tiredness.

Initial assessment

A GP may ask about:

• your symptoms and how they affect your life
• your family history – although rare, pulmonary arterial hypertension can run in families
• any medicine you're currently taking
• any other medical conditions you have

You may also have a physical examination where a GP will listen to your heart and lungs, and check for any swelling in your legs or ankles.

Further tests

If a GP thinks you may have pulmonary hypertension, they'll recommend further tests.

The 2 main tests used to help diagnose the condition are:

• an echocardiogram – a scan that uses high-frequency sound waves to create an image of the heart; it's used to estimate the pressure in your pulmonary arteries and test how well both sides of your heart are pumping
• right heart catheterisation – a thin, flexible tube (catheter) is inserted into a vein in your neck, arm or groin, and passed through to your pulmonary artery to confirm a diagnosis by accurately measuring the blood pressure in the right side of your heart and pulmonary arteries; it's carried out in specialist national pulmonary hypertension centres

Other tests you may have include:

• an electrocardiogram (ECG) – a simple test that can be used to check your heart's rhythm and electrical activity
• a chest X-ray – to check for symptoms such as an enlarged heart or scarring in your lungs, which can cause shortness of breath
• lung function tests – to assess how well your lungs work
• exercise tests – where you carry out some form of exercise while your heart rate, blood pressure and oxygen levels are monitored
• a ventilation-perfusion scan – where the amount of air and blood flow in your lungs is measured; it's used to look for blood clots that may be causing pulmonary hypertension
• blood tests – to rule out other possible conditions, such as thyroid and liver disease

Classifying pulmonary hypertension

If you're diagnosed with pulmonary hypertension, your condition will be classified depending on how severe your symptoms are. This is to help work out the best treatment for you.

It's usually classified into 4 types, where: 

• ordinary physical activities do not cause any symptoms
• ordinary physical activities cause symptoms, such as chest pain or tiredness, but you do not have any symptoms when resting
• even slight physical activities, such as moving your arms, cause symptoms, but you do not have any symptoms when resting
• you have symptoms when resting that get worse with any type of physical activity

Read about how pulmonary hypertension is treated.

Pulmonary hypertension cannot be cured, but treatments can reduce your symptoms and help you manage your condition.

If the cause is identified and treated early, it may be possible to prevent permanent damage to your pulmonary arteries, which are the blood vessels that supply your lungs.

Treating underlying conditions

If pulmonary hypertension is caused by another condition, such as a heart or lung problem, treatments will focus on the underlying condition.

If pulmonary hypertension is caused by blood clots that block the pulmonary arteries, you may be offered anticoagulant medicines to prevent more clots forming. 

You may also be offered an operation known as a pulmonary endarterectomy.

Specialist centres for pulmonary arterial hypertension

If you have pulmonary arterial hypertension (PAH), you'll be referred to a centre that specialises in treating this form of the condition. There are 7 centres in England and 1 in Scotland.

They are:

• Great Ormond Street Hospital for Children, London
• Hammersmith Hospital, London
• Royal Brompton Hospital, London
• Royal Free Hospital, London
• Royal Papworth Hospital NHS Trust, Cambridgeshire
• Royal Hallamshire Hospital, Sheffield
• Freeman Hospital, Newcastle
• Golden Jubilee National Hospital, Glasgow

Treatments for pulmonary arterial hypertension

There are many treatments for pulmonary arterial hypertension (PAH). Which treatment or combination of treatments you'll be offered will depend on a number of factors, including what's causing PAH and the severity of your symptoms.

Treatments include:

• anticoagulant medicines – such as warfarin to help prevent blood clots
• diuretics (water tablets) – to remove excess fluid from the body caused by heart failure
• oxygen treatment – this involves inhaling air that contains a higher concentration of oxygen than normal
• digoxin – this can improve your symptoms by strengthening your heart muscle contractions and slowing down your heart rate

There are also a number of specialist treatments for PAH that help relax the arteries in the lungs and reduce the blood pressure in the lungs.

These medicines slow the progression of PAH, and may even reverse some of the damage to the heart and lungs.

Other treatments that are sometimes used are:

• endothelin receptor antagonists – such as bosentan, ambrisentan and macitentan
• phosphodiesterase 5 inhibitors – sildenafil and tadalafil
• prostaglandins – epoprostenol, iloprost and treprostinil
• soluble guanylate cyclase stimulators – such as riociguat
• calcium channel blockers – nifedipine, diltiazem, nicardipine and amlodipine

You can find detailed information about these treatments for pulmonary hypertension on the Pulmonary Hypertension Association UK website.

Surgery and procedures for pulmonary hypertension

Some people with pulmonary hypertension may need surgery. The 3 types of surgery currently used are:

• pulmonary endarterectomy – an operation to remove old blood clots from the pulmonary arteries in the lungs in people with chronic thromboembolic pulmonary hypertension
• balloon pulmonary angioplasty – a new procedure where a tiny balloon is guided into the arteries and inflated for a few seconds to push the blockage aside and restore blood flow to the lung; it may be considered if pulmonary endarterectomy is not suitable, and has been shown to lower blood pressure in the lung arteries, improve breathing, and increase the ability to exercise
• atrial septostomy – a small hole is made in the wall between the left and right atria of the heart using a cardiac catheter, a thin, flexible tube inserted into the heart's chambers or blood vessels; it reduces the pressure in the right side of the heart, so the heart can pump more efficiently and the blood flow to the lungs can be improved
• transplant – in severe cases, a lung transplant or a heart-lung transplant may be needed; this type of surgery is rarely used because effective medicine is available

The National Institute for Health and Care Excellence (NICE) has guidance on balloon pulmonary angioplasty for chronic thromboembolic pulmonary hypertension.

Pulmonary Hypertension Association UK

Pulmonary Hypertension Association UK is a charity for people with pulmonary hypertension.

The website provides further information and advice about all aspects of the condition, including living with pulmonary hypertension, and support for family and friends.