Primary Pulmonary Hypertension

Primary, or unexplained, pulmonary hypertension (PPH) is a rare lung disorder in which the blood pressure in the pulmonary artery rises far above normal levels for no apparent reason. The pulmonary artery is the blood vessel carrying oxygen-poor blood from the right ventricle, one of the pumping chambers of the heart, to the lungs. In the lungs, the blood picks up oxygen and then flows to the left side of the heart, where it is pumped by the left ventricle to the rest of the body through the aorta.

Hypertension is the medical term for an abnormally high blood pressure. Normal mean pulmonary-artery pressure is approximately 14 mmHg at rest. In the PPH patient, the mean blood pressure in the pulmonary artery is greater than 25 mmHg at rest and 30 mmHg during exercise. This abnormally high pressure (pulmonary hypertension) is associated with changes in the small blood vessels in the lungs, resulting in an increased resistance to blood flowing through the vessels.

This increased resistance, in turn, places a strain on the right ventricle, which now has to work harder than usual against the resistance to move adequate amounts of blood

through the lungs.

The true incidence of PPH is unknown. The first reported case occurred in 1891, when E. Romberg, a German doctor, published a description of a patient who, at autopsy, showed

thickening of the pulmonary artery but no heart or lung disease that might have caused the condition. In 1951, when 39 cases were reported by Dr. D.T. Dresdale in the United States, the illness received its name.

Between 1967 and 1973, a 10-fold increase in unexplained pulmonary hypertension was reported in central Europe. The rise was subsequently traced to aminorex fumarate, an

amphetamine-like drug introduced in Europe in 1965 to control appetite. Only about 1 in1,000 people who took the drug developed PPH. When they stopped taking the drug, some improved considerably; in others, the disease kept getting worse. Once aminorex was removed from the market, the incidence of PPH went down to normal levels.

More recently, in the United States and France, several cases of PPH have been associated with the appetite suppressants, fenfluramine and dexfenfluramine.

In the United States it has been estimated that 300 new cases of PPH are diagnosed each year; the greatest number are reported in women between the ages of 21 and 40.

Indeed, at one time the disease was thought to occur among young women almost exclusively; we now know, however, that men and women in all age ranges, from very young children to elderly people, can develop PPH. Apparently it also affects people of all racial and ethnic origins equally.

There may be one or more causes of PPH; however, all remain unknown. The low incidence makes learning more about the disease extremely difficult. Studies of PPH also have been difficult because a good animal research model of the disease has not been available.

Researchers think that in most people who develop PPH the blood vessels are particularly sensitive to certain internal or external factors and constrict, or narrow, when exposed

to these factors. For example, people with Raynaud's disease seem more likely than others to develop PPH; Raynaud's disease is a condition in which the fingers and toes turn blue when cold because the blood vessels in the fingers and toes are particularly sensitive to cold. Diet suppressants, cocaine, HIV, and pregnancy are some of the factors that are thought to trigger constriction, or narrowing, in the pulmonary artery.

In about 6 percent to 10 percent of cases, PPH is familial; that is, it is inherited from other family members. The familial form of PPH is similar to the more common form of the disease, sometimes referred to as "sporadic" PPH.

Researchers believe that one of the ways PPH starts is with injury to the layer of cells (the endothelial cells) that line the small blood vessels of the lungs. This injury, which occurs for unknown reasons, may bring about changes in the way the endothelial cells interact with smooth muscle cells in the vessel wall. As a result, the smooth muscle contracts more than normal and thereby narrows the vessel.

The process eventually results in the development of extra amounts of tissue in the walls of the pulmonary arteries. The amount of muscle increases in some arteries, and muscle

appears in the walls of arteries that normally have no muscle.With time, scarring, or fibrosis, of the arteries takes place, and they become stiff as well as thickened. Some vessels may become completely blocked. There is also a tendency for blood clots to form within the smaller arteries.

In response to the extra demands placed on it by PPH, the heart muscle gets bigger, and the right ventricle expands in size. Overworked and enlarged, the right ventricle gradually

becomes weak and loses its ability to pump enough blood to the lungs. Eventually, the right side of the heart may fail completely, resulting in death.

In general, researchers find there is no correlation between the time PPH is thought to have started, the age at which it is diagnosed, and the severity of symptoms. In some patients, especially children, the disease progresses fairly rapidly.

The first symptom is frequently fatigue, with many patients thinking they tire easily because they are simply out of shape. Difficulty in breathing (dyspnea), dizziness,

and even fainting spells (syncope) are also typical early symptoms. Swelling in the ankles or legs (edema), bluish lips and skin (cyanosis), and chest pain (angina) are among other symptoms of the disease.

Patients with PPH may also complain of a racing pulse; many feel they have trouble getting enough air. Palpitations, a strong throbbing sensation brought on by the increased rate of the heartbeat, can also cause discomfort.

Some people with PPH do not seek medical advice until they can no longer go about their daily routine. The more severe the symptoms, the more advanced the disease. In these more advanced stages, the patient is able to perform only minimal activity and has symptoms even when resting. The disease may worsen to the point where the patient is completely bedridden.

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