What causes pulmonary hypertension?
There are 5 main groups of pulmonary hypertension, as it can be caused by different things.
- Group 1: Pulmonary arterial hypertension (PAH)
- Group 2: Pulmonary hypertension caused by left heart disease
- Group 3: Pulmonary hypertension caused by lung conditions or lack of oxygen
- Group 4: Pulmonary hypertension caused by blood clots (chronic thromboembolic pulmonary hypertension, CTEPH)
- Group 5: Pulmonary hypertension caused by a range of causes
This group is rare. It’s caused by changes to very small arteries, which take blood from the right side of your heart to your lungs. The walls of the arteries get thicker and stiffer. This makes the space for blood to pass through narrower, which, in turn, increases the blood pressure.
It can be inherited. It’s also associated with connective tissue diseases, liver disease, congenital heart defects, HIV and certain drugs. When no cause is found, it is called ‘idiopathic’.
pulmonary artery in a healthy person (left) and in someone with pulmonary arterial hypertension
The left side of your heart is the high-pressure system that pumps blood to the rest of your body. If there are problems with how the left heart works, blood can’t flow easily through your lungs into the left hand side of your heart.
As a result, the right side of your heart has to work harder to pump blood through your lungs. This increases the blood pressure in your pulmonary arteries.
This is one of the most common causes of pulmonary hypertension.
The common causes in this group are:
- chronic obstructive pulmonary disease (COPD)
- interstitial lung disease (such as pulmonary fibrosis)
- obstructive sleep apnoea (OSA)
These conditions reduce the amount of oxygen getting into your lungs. When there’s a low level of oxygen, your pulmonary arteries get narrower. This increases the lung blood pressure. Lung diseases can also damage blood vessels directly.
This is another common cause of pulmonary hypertension.
pulmonary artery in a healthy person (left) and in someone with a lung condition
Group 4: Pulmonary hypertension caused by blood clots (chronic thromboembolic pulmonary hypertension, CTEPH)
This is a rare condition. It occurs when blood clots (pulmonary embolism) block the flow of blood in arteries and blood pressure in the lungs increases. Normally blood clots dissolve once you get anticoagulant drugs. But rarely blood clots fail to dissolve and form scars instead, blocking the flow of blood.
pulmonary artery in a healthy person (left) and in someone with blood clots
This is a mixed group of rare causes. They’re grouped together because their causes are less clear.