The typical heart has two upper chambers and two lower chambers. Each time blood moves through the heart, the lower right chamber pumps blood to the lungs. The blood passes through a large blood vessel called the pulmonary artery.
Blood usually flows easily through blood vessels in the lungs to the left side of the heart. These blood vessels are the pulmonary arteries, capillaries and veins.
But changes in the cells that line the lung arteries can cause the artery walls to become narrow, stiff, swollen and thick. These changes may slow down or stop blood flow through the lungs, causing pulmonary hypertension.
Pulmonary hypertension is classified into five groups, depending on the cause.
Group 1: Pulmonary arterial hypertension (PAH)
Causes include:
- Unknown cause, called idiopathic pulmonary arterial hypertension.
- Changes in a gene passed down through families, called heritable pulmonary arterial hypertension.
- Use of some medicines or illegal drugs, including methamphetamine.
- Heart problems present at birth, called a congenital heart defect.
- Other health conditions, including scleroderma, lupus and chronic liver disease such as cirrhosis.
Group 2: Pulmonary hypertension caused by left-sided heart disease
This is the most common form of pulmonary hypertension. Causes include:
- Left heart failure.
- Left-sided heart valve disease such as mitral valve or aortic valve disease.
Group 3: Pulmonary hypertension caused by lung disease
Causes include:
- Scarring of the lungs, called pulmonary fibrosis.
- Chronic obstructive pulmonary disease.
- Sleep apnea.
- Long-term exposure to high altitudes in people who may be at higher risk of pulmonary hypertension.
Group 4: Pulmonary hypertension caused by chronic blood clots or blockages in the pulmonary artery
Causes include:
- Chronic blood clots in the lungs, called pulmonary emboli.
- Tumors that block the pulmonary artery.
Group 5: Pulmonary hypertension triggered by other health conditions
Causes include:
- Blood disorders, including polycythemia vera and essential thrombocythemia.
- Inflammatory disorders such as sarcoidosis.
- Metabolic disorders, including glycogen storage disease.
- Kidney disease.
Eisenmenger syndrome and pulmonary hypertension
Eisenmenger syndrome is a type of congenital heart disease that causes pulmonary hypertension. It can occur with unrepaired holes between the heart chambers. An example is a large hole in the heart between the two lower heart chambers called a ventricular septal defect.
The hole in the heart causes blood to flow incorrectly in the heart. Oxygen-rich blood mixes with oxygen-poor blood. The blood then returns to the lungs instead of going to the rest of the body. This increases the blood flow and pressure in the pulmonary arteries, causing pulmonary hypertension.