Pulmonary Hypertension
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 Section 3, Chapter 25).
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 Section 14, Chapter 178). 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 Section 4, Chapter 46), 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.
 See the sidebar Cor Pulmonale: A Disorder Stemming From Pulmonary Hypertension.
Causes
There are two types of pulmonary hypertension: primary and secondary. Primary pulmonary hypertension is much less common than secondary pulmonary hypertension. In primary pulmonary hypertension, the cause is not known, but likely begins with spasm (contraction) of the muscle layer in the pulmonary arteries. Women are affected by primary pulmonary hypertension twice as often as men, and half of the people are 35 or older at the time of diagnosis. Secondary pulmonary hypertension means that the condition occurred because of another disorder that affects lung structure or function.
Secondary pulmonary hypertension can be caused by any disease that impedes the flow of blood through the lungs or that causes sustained periods of low oxygen in the blood. One of the most common causes is chronic obstructive pulmonary disease (see Section 4, Chapter 45). When the lungs are impaired by disease, it takes more effort to pump blood through them. Over time, chronic obstructive pulmonary disease destroys the small air sacs (alveoli) together with their small vessels (capillaries) in the lungs. The single most important cause of pulmonary hypertension in chronic obstructive pulmonary disease is the narrowing of the pulmonary artery that occurs as a result of low blood oxygen levels.
Another disease that can cause pulmonary hypertension is pulmonary fibrosis (see Section 4, Chapter 50), which causes extensive scar tissue to form in the lungs. The scar tissue destroys the pulmonary circulation and makes blood flow more difficult. Other lung diseases that may cause pulmonary hypertension include cystic fibrosis (see Section 4, Chapter 53) and certain occupational lung diseases, such as asbestosis (see Section 4, Chapter 49) and silicosis (see Section 4, Chapter 49).
Less often, pulmonary hypertension is caused by extensive loss of lung tissue from surgery or trauma, or by heart failure, scleroderma, obesity with reduced ability to breathe (Pickwickian syndrome), neurologic diseases involving the respiratory muscles, chronic liver disease, HIV infection, and diet drugs (for example, dexfenfluramine-phentermine [fen-phen]). A sudden cause of pulmonary hypertension is pulmonary embolism (see Section 4, Chapter 46), a condition in which blood clots become lodged in the arteries of the lung, causing serious problems.
Symptoms
Shortness of breath upon exertion is the most common symptom of pulmonary hypertension, and virtually everyone who has the condition develops it. Some people feel light-headed or fatigued upon exertion, and an angina-like chest pain is common. The person is likely to feel weak because body tissues are not receiving enough oxygen. Other symptoms, such as coughing and wheezing, are usually caused by the underlying lung disease. Swelling (edema), particularly of the legs, may occur because fluid may leak out of the veins and into the tissues, but this is usually a sign that cor pulmonale has developed.
Some people with pulmonary hypertension have connective tissue disorders, especially scleroderma (see Section 5, Chapter 68); when people have both conditions, Raynaud's phenomenon often develops before symptoms of pulmonary hypertension appear, sometimes as long as years earlier (see Section 3, Chapter 34).
For unknown reasons, some people with primary pulmonary hypertension develop achy joints, often years before the apparent onset of the disorder.
Diagnosis
Based on the symptoms, a doctor may suspect pulmonary hypertension in people who have an underlying lung disorder. A chest x-ray may show that the pulmonary arteries are enlarged. An electrocardiogram and an echocardiogram enable the doctor to look for certain problems with the right side of the heart even before cor pulmonale develops. For example, thickening of the right ventricle or a partial reversal (back flow) of blood through the tricuspid valve between the right atrium and right ventricle may be detected on an echocardiogram. Pulmonary function tests help the doctor assess the extent of lung damage. A sample of blood may be taken from an artery in an arm to measure the level of oxygen in the blood.
A definite diagnosis of pulmonary hypertension usually requires passing a tube through a vein in an arm or a leg into the right side of the heart to measure the blood pressure in the right ventricle and the pulmonary artery.
Treatment
Treatment of secondary pulmonary hypertension is often directed at the underlying lung disease. Vasodilators (drugs to dilate blood vessels), such as calcium channel blockers, nitric oxide, and prostacyclin, are often helpful for secondary pulmonary hypertension associated with scleroderma, chronic liver disease, and HIV infection. In contrast, these drugs have not been proven effective for people with secondary pulmonary hypertension due to an underlying lung disease. For most people with primary pulmonary hypertension, vasodilators, such as prostacyclin, drastically reduce blood pressure in the pulmonary arteries. Prostacyclin given intravenously through a catheter surgically implanted in the skin improves the quality of life, increases survival, and reduces the urgency of lung transplantation. However, a doctor will first test the effectiveness of vasodilators in a given person in a cardiac catheterization laboratory, because their use may be dangerous in some people. A subcutaneous (under the skin) form of prostacyclin is now available and has been effective in some people.
Bosentan, a new drug given by mouth, has been effective in some people. A drug similar to prostacyclin, called iloprost, can be administered by inhalation and, as a result, has a much lower risk of complications than prostacyclin. However, this drug is not available in the United States.
If a person with pulmonary hypertension has a low oxygen level in the blood, the continuous use of oxygen through nasal prongs or an oxygen mask may reduce blood pressure in his pulmonary arteries and may help relieve his shortness of breath. A diuretic drug may improve the exchange of gases in the lungs, presumably by relieving the buildup of fluid as well as diminishing the buildup of fluid in the rest of the body. An anticoagulant may be prescribed to reduce the risk of blood clots and subsequent pulmonary embolism (see Section 4, Chapter 46).
Single or double lung transplantation is an established procedure for treating primary pulmonary hypertension. Without a transplant, most people die 2 to 5 years after the disease is diagnosed. Transplantation may be a possible treatment for severe secondary pulmonary hypertension if treatment of the underlying disorder fails.
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