PAH Overview

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What is pulmonary arterial hypertension?

Pulmonary arterial hypertension (PAH) is a disorder that affects the pulmonary artery—the large blood vessel that carries blood from the heart to the lungs—and the hundreds of tiny blood vessels that branch off from it.

PAH starts when the small vessels that supply blood to the lungs constrict, or tighten up. This makes it more difficult for blood to get through to the lungs, and as a result the heart must pump harder. Over time, scarring (fibrosis) of the blood vessels makes them stiffer and thicker, and some may become completely blocked. The extra stress causes the heart to enlarge and become less flexible. As this cycle continues, less and less blood is able to flow out of the heart, through the lungs, and into the body, and more and more symptoms can begin to appear.

Healthy blood vessels have a balance of naturally occurring chemicals. In PAH, the balance is disturbed. There is too much of some chemicals and too little of others.¹ One of these naturally occurring chemicals is called prostacyclin, which helps widen or dilate blood vessels.² In patients with PAH, there is not enough prostacyclin found in the blood vessels.

Another naturally occurring substance is called endothelin, which plays a role in regulating blood flow. With PAH, too much endothelin is produced in the body. This extra endothelin may cause blood vessels to tighten.

Statements are based on observations reported from in vitro or animal trials. The clinical significance in humans is unknown.

Feeling breathless

In PAH, the resistance in the blood vessels makes it harder for your heart to pump blood into your lungs. Less blood gets to the lungs to pick up the oxygen your body needs. This causes less oxygen to get into the cells of your body, making you feel short of breath.³

Causes of PAH

There are four general causes for pulmonary arterial hypertension (PAH):

• Inherited: PAH can be passed down to you genetically from your parents
• Certain medications or drugs: Taking the phen-fen diet drug combination, cocaine, or methamphetamines, for example, can lead to PAH⁴
• Underlying disease: Also known as secondary PAH; underlying diseases can create the conditions that lead to PAH. Secondary PAH may be associated with certain medical conditions including:
  • Collagen vascular disease, also known as "connective tissue disease." This includes diseases such as scleroderma, lupus (systemic lupus erythematosus), rheumatoid arthritis, and others
  • Congenital heart disease
  • HIV infection
  • Sickle cell disease
• No known cause: Also known as "idiopathic," this common type of PAH means that scientists haven't yet uncovered the entire process that leads to PAH.

The good news is that research is ongoing and scientists and physicians know much more about how PAH develops and how to control it today than they did ten years ago. Although a cure has not yet been found, much progress has been made in terms of understanding the disease and multiple treatments are now available.⁴

References: 1. McLaughlin V, McGoon MD. Pulmonary arterial hypertension. Circulation. 2006;114:1417-1431. 2. National Heart Lung and Blood Institute. Available at http://www.nhlbi.nih.gov/health/dci/Diseases/pah/pah_what.html. Accessed October 10, 2007. 3. Gaine SP, Rubin LJ. Primary pulmonary hypertension. Lancet. 1998;352:719-725. 4. Gibbs J. Making a Diagnosis in PAH. Eur Respir Rev. 2007;16:102,8-12.