What is pulmonary hypertension?
The human body has two major areas of blood vessels that distribute from, and return blood to, the left and right heart. The portion of the circulation that distributes the blood from the left side of the heart, throughout the body, is referred to as the systemic circulation. The portion of the circulation that distributes the blood from the right side of the heart, to the lungs, is referred to as the pulmonary (lung) circulation.

The left ventricle of the heart pumps oxygenated blood from the lungs into the systemic circulation. When a doctor or a nurse measures the blood pressure on a person's arm, he/she is measuring the pressures in the systemic circulation. When these pressures are abnormally high, the person is diagnosed as having high blood pressure (hypertension).

The right ventricle pumps venous blood returning from the body into the arteries of the lungs to receive oxygen. The pressures in the lung arteries (pulmonary arteries) are normally significantly lower than the pressures in the systemic circulation. When pressure in the pulmonary circulation becomes abnormally elevated, it is referred to as pulmonary hypertension.

What causes pulmonary hypertension?

Pulmonary hypertension results from constriction, or tightening, of the blood vessels that supply blood to the lungs. Consequently, it becomes difficult for blood to pass through the lungs, making it harder for the heart to pump blood forward. This stress on the heart leads to enlargement of the heart and eventually fluid can build up in the liver and tissues, such as the in the legs. Affected patients can sometimes notice increasing shortness of breath and dizziness.

Pulmonary hypertension can be caused by diseases of the heart and the lungs, such as chronic obstructive pulmonary disease (COPD) or emphysema, failure of the left heart ventricle, recurrent pulmonary embolism (blood clots traveling from the legs or pelvic veins obstructing the pulmonary arteries), or underlying diseases such as scleroderma. Pulmonary hypertension can also be caused by chronic low blood oxygen levels as in some patients with sleep apnea. Pulmonary hypertension caused by other illnesses is called secondary pulmonary hypertension.

When pulmonary hypertension occurs without underlying heart and lung disease or other illnesses, it is called primary pulmonary hypertension. Primary pulmonary hypertension is more common in young females. Recently this condition has been rarely reported with the use of anti-obesity drugs such as Redux and Fen/Phen.

Tests used to evaluate patients with suspected pulmonary hypertension include chest x-ray and high-resolution CAT scanning, pulmonary function tests, and echocardiogram. Right heart catheterization (angiogram) can be used to confirm the diagnosis.

What is the treatment for pulmonary hypertension?

Treatment of pulmonary hypertension involves treating the underlying causes, using supplemental oxygen to increase blood oxygen levels, diuretics, blood thinning medications, and medications that dilate blood vessels such as calcium channel blockers. Bosentan (Tracleer), a medication that widens narrowed blood vessels in the pulmonary circulation, and is approved as a treatment for pulmonary hypertension that is taken in tablet form. Intravenous prostacyclin is also used in severe situations. Despite advances in various treatments, there is no cure for pulmonary hypertension.

Low oxygen in the atmosphere causes low blood oxygen levels and aggravates pulmonary hypertension. Therefore, patients with pulmonary hypertension may benefit from breathing supplemental oxygen, even temporarily during air travel or traveling to high altitude destinations.

Recent studies have shown some benefit in using sildenafil to reduce the pressure in the pulmonary arteries. Potential future therapies being studied by medical scientists include nitric oxide.

What is primary pulmonary hypertension and what causes it?

Primary pulmonary hypertension has no identifiable underlying cause. Primary pulmonary hypertension is also refered to as idiopathic pulmonary hypertension.

Primary pulmonary hypertension is an unusually aggressive and often fatal form of pulmonary hypertension that commonly affects young people. Whereas it is known that the arterial obstruction is caused by a building up of the smooth muscle cells that line the arteries, the underlying cause of the disease has long been a mystery.

A genetic cause of the familial form of primary pulmonary hypertension has been discovered. It is caused by mutations in a gene called BMPR2. BMPR2 encodes a receptor (a transforming growth factor beta type II receptor) that sits on the surface of cells and binds molecules of the TGF-beta superfamily. Binding triggers conformational changes that are shunted down into the cell's interior where a series of biochemical reactions occur, ultimately affecting the cell's behavior. The mutations block this process. This discovery provides a means of genetic diagnosis and a potential target for the therapy of people with familial (and possibly also sporadic) primary pulmonary hypertension.

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