First, a few words of reassurance. It's natural to feel confused and anxious after being diagnosed with pulmonary arterial hypertension. The condition is not exactly a household word, and it is a serious illness. Pulmonary hypertension often requires treatment by specialists at large medical centers with specific expertise. Being diagnosed with the condition may also require you to make significant changes in your life.

But keep in mind that many people with pulmonary arterial hypertension can manage the disease and live their lives quite normally. New advances in the understanding of this condition and how to treat it have changed the outlook dramatically in recent years.

"Pulmonary" is from the Latin root "pulmo," or "the lung." "Hypertension" means high blood pressure. Pulmonary hypertension is a condition caused by abnormally high blood pressure in the arteries that supply the lungs with blood.

Most people are familiar with blood pressure as measured with a cuff that goes around the upper arm. This simple test charts the pressure in blood vessels in the body's extremities. If elevated, this is referred to simply as "hypertension."

Pulmonary hypertension, in contrast, is abnormally high blood pressure in just one part of the body: the vessels that supply blood to the lungs. Normally, the pressure in these vessels is much lower than that in the rest of the body. Typical blood pressure measured with a cuff around your arm is 120/80 mm Hg. Normal pulmonary artery blood pressure is only about 25/15 mm Hg.

The World Health Organization divides pulmonary hypertension into five groups, based on causes of the disease. Group 1 is pulmonary arterial hypertension, or PAH; until recently, it was known as primary pulmonary hypertension. Groups 2-5 are collectively known as secondary arterial hypertension.

Like other forms of pulmonary hypertension, PAH occurs when blood pressure in the pulmonary arteries is dangerously high – more than 15 mm Hg at rest and more than 30 mm Hg during physical activity. Pulmonary arterial hypertension includes cases of PAH with no known cause, PAH that’s inherited, and PAH that’s caused by conditions such as HIV infection, certain liver and thyroid diseases, congenital heart disease (heart disease that’s present at birth), and the use of certain diet medications or street drugs such as cocaine.

Regardless of the cause, all types of pulmonary hypertension can take a harmful course without treatment. When pulmonary blood pressure becomes abnormally high, it can seriously damage the heart and lungs. Pulmonary arterial hypertension often occurs when blood vessels become narrowed or blood flow through these vessels is hindered. The pressure of blood moving through the constricted passage increases, just the way water pressure increases if you hold your thumb over the end of a garden hose. Elevated blood pressure can increase the risk of injury to blood vessels. It also puts an extra strain on the heart, which has to work harder to pump blood through narrowed or partially blocked vessels.

In the case of pulmonary hypertension, the right ventricle (the muscle of the right side of the heart that pumps blood to the lungs) has to work harder. The added strain causes the muscle to enlarge and become less efficient.

The extra pressure within the vessels also puts strain on their inner walls, causing them to become stiffer and thicker. Some vessels may gradually become completely blocked. Other complications, such as low oxygen levels, can also ensue. In some people the body begins to produce more red blood cells to make up for lowered levels of oxygen in the blood. This causes blood to become thicker and stickier, further increasing the load on the heart and raising the risk of blood clots.

Pulmonary arterial hypertension is a challenging illness. But there is much that doctors can do to control the problem and treat the symptoms. Newly developed drugs can lower pulmonary blood pressure and reduce the strain on heart muscles. This can allow people with pulmonary hypertension to lead longer and more active lives. Thanks to these advances, the death rate from pulmonary hypertension has dropped significantly in the last few years. Understanding all you can about pulmonary hypertension is an important part of a comprehensive treatment plan.

-- 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.

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

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