Pulmonary hypertension, or PH, is abnormally high pressure in the pulmonary arteries. These arteries carry blood from your heart to your lungs to gather oxygen.

The World Health Organization divides pulmonary hypertension into five groups. Group 1 is primary arterial hypertension, or PAH. It’s a rare disease; only 1,000 new cases are diagnosed in the United States each year. Groups 2-5 are sometimes called secondary pulmonary hypertension.

Researchers do not know what causes some cases of pulmonary arterial hypertension. One reason it remains a mystery is that it affects so few people. Its rarity makes it difficult for scientists to learn more about it. In the last four decades, two puzzling outbreaks of pulmonary hypertension led medical sleuths to a surprising suspect: appetite suppressants. Between 1967 and 1973, the number of recorded cases of pulmonary hypertension jumped tenfold in Europe. Medical detectives traced the outbreak to a weight-loss drug called aminorex fumarate, which was introduced in 1965 in Europe. When the drug was withdrawn, the number of cases fell. More recently, health experts in the United States detected another spike in cases of primary pulmonary hypertension. The epidemic was traced to two new prescription weight-loss drugs, fenfluramine and dexfenfluramine. Both have since been withdrawn from the market.

Some experts speculate that people who develop the disease have blood vessels that are abnormally sensitive to certain factors. Cocaine use, the HIV virus, and the diet drugs noted above are among the suspected factors, but there are no doubt others. In some people, these factors may make the lining of the pulmonary arteries particularly susceptible to damage. However, most people with these factors don't go on to develop pulmonary hypertension.

Why some people are at increased risk of PAH is largely unknown. Women are at significantly higher risk than men, but why women are more susceptible remains a puzzle.

The genetic link to this mystifying illness is better known. Scientists have learned, for example, that pulmonary arterial hypertension sometimes runs in families. Researchers have identified the gene involved, which is called BMPR2. (There may be other genes involved that aren’t yet identified.) Because of the family connection, doctors often recommend that other close relatives of the family be tested when one person has been diagnosed with PAH. But inherited PAH is exceedingly rare. Fewer than 100 families in the United States have been found in which the disease has occurred in at least two first-degree relative (parent, child, sibling). The likelihood of a first-degree relative being affected when only one person in the family is known to have pulmonary arterial hypertension is estimated to be 0.6 to 1.2 percent, according to a WHO-sponsored world symposium on the disease.

Research into the genetic factors linked to PAH has begun to offer clues about what may cause the disease. Mutations of the BMPR2 gene interrupt normal signals to cells in blood vessel linings, causing them to multiply abnormally. In turn, the inner walls and the smooth muscles of pulmonary arteries thicken, researchers speculate. Scarring, or fibrosis, can also occur.

Other causes of PAH include congenital heart disease (heart disease present at birth), HIV infection, liver and thyroid disease, and the use of certain street drugs such as cocaine.

Pulmonary arterial hypertension of unknown origin (also known as idiopathic PAH, or IPAH) is diagnosed when doctors are unable to identify other medical conditions that might be causing the dangerously high blood pressure in pulmonary arteries. As a result, it remains a difficult disease to treat. Physicians can try to alleviate the symptoms and ease the strain on the heart and lungs by lowering the pulmonary blood pressure.

Secondary pulmonary hypertension is far more common than PPH. Because it frequently goes undiagnosed, researchers don't know precisely how many people suffer from secondary pulmonary hypertension. Most cases are only recognized when the symptoms become serious enough for people to seek medical attention.

Causes of secondary pulmonary hypertension can include autoimmune disorders such as lupus or scleroderma, conditions that affect the left side of the heart, COPD, emphysema, pulmonary fibrosis, sarcoidosis, blood clots in pulmonary arteries, sickle cell disease, sleep disorders such as sleep apnea, tumors that press on the pulmonary blood vessels, and other conditions. In some cases, doctors can treat the underlying problem and reduce blood pressure in the pulmonary arteries. In others, they treat the symptoms of elevated pulmonary pressure.

-- Peter Jaret is a contributing editor for Health magazine and a winner of the American Medical Association's award for medical reporting. His work has appeared in National Geographic, Newsweek, Hippocrates, and many other national magazines. He is also the author of In Self-Defense (Harcourt Brace Jovanovich), Active Living Every Day, and Heart Healthy for Life.

References

The Rush Heart Institute Center for Pulmonary Heart Disease, www.rush.edu

Last updated August 18, 2009
Copyright © 2003 Consumer Health Interactive

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