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
- 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.