What Is Pulmonary Arterial Hypertension?

Pulmonary arterial hypertension (PAH) is continuous high blood pressure in the pulmonary artery. The average blood pressure in a normal pulmonary artery is about 14 mmHg when the person is resting. In PAH, the average is usually greater than 25 mmHg.

PAH is a serious condition for which there are treatments but no cure, and treatment benefits many patients.

The pulmonary artery is the blood vessel that carries oxygen-poor blood from the right ventricle in the heart to the small arteries in the lungs. In PAH, 3 types of changes may occur in the pulmonary arteries:

• The muscles within the walls of the arteries may tighten up. This makes the inside of the arteries narrower.
  
  
• The walls of the pulmonary arteries may thicken as the amount of muscle increases in some arteries. Scar tissue may form in the walls of arteries. As the walls thicken and scar, the arteries become increasingly narrow.
  
  
• Tiny blood clots may form within the smaller arteries, causing blockages.

There is less room for the blood to flow through these narrower arteries. The arteries may also stiffen. Over time, some of the arteries may become completely blocked.

The narrowing of the pulmonary arteries causes the right side of heart to work harder to pump blood through the lungs. Over time, the heart muscle weakens and loses its ability to pump enough blood for the body's needs. This is called right heart failure. Heart failure is the most common cause of death in patients with PAH.

There are 2 types of PAH:

• Primary (PPAH) is inherited or occurs for no known reason.
  
  
• Secondary (SPAH) is caused by, or occurs because of another condition. The conditions include chronic heart or lung disease, blood clots in the lungs, or a disease like scleroderma (skler-o-'d&r-m;&).

About 300 new cases of PPAH are diagnosed in the United States each year. SPAH is much more common.

Doctors have learned a lot about PAH in recent years. More treatments are now available. Researchers are also studying several promising new treatments that may prolong lives, as well as improve the quality of life.