Pulmonary hypertension (PH) is a rare lung disorder occurring as a primary idiopathic disease or as a complication of a large number of respiratory and cardiac diseases. PH can occur with or without an identifiable cause.

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.

When a person has PH, the blood pressure in the pulmonary artery rises far above normal levels. 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 PH 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.

Pulmonary Hypertension (PH) is rarely picked up in a routine medical examination. Even in its later stages, the signs of the disease can be confused with other conditions affecting the heart and lungs. Thus, much time can pass between the time the symptoms of PH appear and a definite diagnosis is made.

Pulmonary Hypertension remains a diagnosis of exclusion. This means that it is diagnosed only after the doctor finds elevated blood pressure in the lungs and excludes or cannot find other reasons for the hypertension, such as a chronic obstructive pulmonary disease (chronic bronchitis and emphysema), blood clots in the lung (pulmonary thromboemboli), or some forms of congenital heart disease. The first tests for PH help the doctor determine how well the heart and lungs are performing. If the results of these tests do not give the doctor enough information, the doctor must perform a cardiac catheterization. The procedure, discussed below, is the way the doctor can make certain that the patient's problems are due to PH and not to some other condition.

Up until 1990, there were very few treatments available for pulmonary hypertension and the projected survival rate was two to four years. Since that time, a number of treatments have become available that are able to slow progression of the disease and even reverse some of the damage to lungs and heart. Still newer treatments are in the research phase or in clinical trial stages. Before a treatment can be prescribed, it is important for the treating physician to determine the type of pulmonary hypertension a patient has and, if possible, determine the cause of PH. If PH is caused by some other disease or condition, the cause must be treated in addition to treating PH.