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Pulmonary weakness

Condition Overview:

A condition in which blood pressure in the arteries of the lungs (pulmonary arteries) is abnormally high.

Blood travels from the right side of the heart through the pulmonary arteries into the lungs. There, carbon dioxide is removed from the blood and oxygen is added to it. Normally, the right side of the heart is weaker than the left side, because relatively little muscle and effort are needed to push the blood through the pulmonary arteries. In contrast, the left side of the heart is stronger and more muscular because it has to push blood through the entire body. Likewise, blood pressure through the pulmonary arteries is lower than that of the general circulation. While the pressure in the general circulation is normally about 120/80 mm Hg, in the pulmonary arteries it is only 25/15 mm Hg.If the pressure of the blood in the pulmonary arteries is abnormally high, the condition is called pulmonary hypertension. Over time, the increased pressure damages both the large and small pulmonary arteries. The walls of the smallest blood vessels thicken and are no longer able to transfer oxygen and carbon dioxide normally between the blood and the lungs. Thus, the levels of oxygen in the blood may fall. The low oxygen level can cause narrowing (constriction) of the pulmonary arteries. These changes contribute further to the increased pressure in the pulmonary circulation.

With pulmonary hypertension, the right side of the heart must work harder to push the blood through the pulmonary arteries into the lungs. Over time, the right ventricle becomes thickened and enlarged, leading to a condition called cor pulmonale. Heart failure develops (see Heart Failure).In some people, the bone marrow produces more red blood cells to compensate for less oxygen in the blood, leading to a condition called polycythemia (see Myeloproliferative Disorders: Polycythemia Vera). The extra red blood cells cause the blood to become thicker and stickier, further increasing the load on the heart. These changes also put a person with cor pulmonale at increased risk of pulmonary embolism (see Pulmonary Embolism), because the thickened blood may clump and form clots, mainly in the veins of the legs. These clots can dislodge and travel to the lungs.

Cor pulmonale and pulmonary hypertension are sometimes thought of as synonymous, but they are not. Pulmonary hypertension is the underlying cause of cor pulmonale. Everyone who has cor pulmonale has pulmonary hypertension. However, a person can have pulmonary hypertension and not have cor pulmonale, although pulmonary hypertension often eventually leads to cor pulmonale.