Pulmonary Circulation: Pulmonary Hypertension

Pulmonary circulation is the circulation of blood through the lungs and is comprised of a system of blood vessels that form a closed circuit between the heart and the lungs. The circulation occurs as follows:

Veins bring oxygen poor blood back to the heart, entering the right atrium throughout two large veins called vena cavae. The right atrium fills with the oxygen poor blood and then contracts, pushing the blood through a one-way valve into the right ventricle. The right ventricle fills and then contracts, pushing the blood into the lungs through the pulmonary arteries (the only arteries in the body that carry oxygen-poor blood).

After the blood obtains oxygen and releases carbon dioxide in the lungs, it returns to the heart via the pulmonary veins (the only veins in the body that carry oxygen-rich blood). Then the oxygen rich blood re-enters the heart through the left atrium and passes into the left ventricle. The left ventricle contracts forcing the blood into the aorta and the blood begins its journey carrying oxygen throughout the body.

Primary pulmonary hypertension is a break down of pulmonary circulation and develops in the following manner:

In the lungs there are thousands of capillaries that export oxygen rich blood and import oxygen depleted blood for oxygen renewal. The interior of these capillaries are lined with endothelial cells (cells that prevent blood from leaking out). The outer walls are made up of a muscle type cells that expands and contracts to propel blood through the blood vessel. When Primary Pulmonary Hypertension occurs, the endothelial cells are weakened so that they allow leakage. This leakage in turn causes the muscles type cells surrounding the blood vessels to constrict and inhibit blood flow. The constriction gradually worsens, increasing the pulmonary arterial pressure, and eventually causing a condition called right ventricular hypertrophy.

The median survival rate for primary pulmonary hypertension after diagnosis is less than two and a half years. Medical management of PPH consists of anticoagulants, oral vasodilators (which are effective only in 20%-25% of cases), continuous intravenous infusions of prostacyclin, diuretics, and supplemental oxygen.

Because of the subtle development of symptoms, early detection of PPH is unlikely and even when it is suspected, a series of multiple tests to either confirm or dismiss the possibility of this diagnosis are required.

No one is certain as to what causes this disease, but the use of certain appetite suppressants as Pondimin (fenfluramine), Redux (dexfenfluramine) and Fen Phen, have been found to greatly increase the risk of developing PPH. An echocardiogram is a good tool for detecting elevated pulmonary artery pressures. However, with some patients, a cardiac catheterization is the only way to confirm the diagnosis.


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