What is pulmonary hypertension?
Primary pulmonary hypertension begins as hypertrophy of the small arteries of the lungs. The medial and intimal muscle layers of these blood vessels thicken, decreasing reflexibility and increasing resistance. The disorder then progresses to vascular sclerosis (narrowing) and the destruction of small blood vessels. Because this form of pulmonary hypertension occurs in association with collagen diseases, it is thought to result from altered immune mechanisms.
Usually, pulmonary hypertension is secondary to hypoxemia (low oxygen levels) from an underlying disease process, including alveolar hypoventilation (insufficient respiration) from Chronic obstructive pulmonary disease (COPD), sarcoidosis, diffuse interstitial pneumonia, malignant metastases, and scleroderma. These diseases may cause pulmonary hypertension through alveolar destruction and increased pulmonary vascular resistance. Other disorders that cause alveolar hypoventilation without lung tissue damage include obesity and kyphoscoliosis. Vascular obstruction may occur because of pulmonary embolism, vasculitis, or disorders that cause obstructions of small or large pulmonary veins, such as fibrosing mediastinitis or mediastinal neoplasm.
Heart disease is another underlying possible cause of pulmonary hypertension. Congenital or acquired heart disease that causes left-to-right shunting of blood—such as patent ductus arteriosus and atrial or ventricular septal defect—increases blood flow into the lungs and consequently raises pulmonary vascular pressure. Acquired heart disease, such as rheumatic valvular disease and mitral stenosis, increases pulmonary venous pressure by restricting blood flow returning to the heart.
The symptoms of pulmonary hypertension include complaints of increasing dyspnea (shortness of breath) on exertion, weakness, syncope, and fatigue. Many patients also show signs of heart failure, including peripheral edema (swelling), ascites (fluid in the abdomen), neck vein distention, and hepatomegaly (enlarged liver). Characteristic diagnostic findings in patients with pulmonary hypertension include abnormalities associated with the underlying disorder heard on auscultation; hypoxemia, determined by arterial blood gases; right ventricular hypertrophy, as diagnosed by electrocardiogram; increased pulmonary artery pressures, with pulmonary systolic pressure above 30 millimeters of mercury and pulmonary capillary wedge pressure increased; filling defects in the pulmonary vasculature, detected by pulmonary angiography; and decreased flow rates and increased residual volume found on pulmonary function testing.
Secondary pulmonary hypertension is difficult to recognize clinically in the early stages, when symptoms and signs are primarily those of the underlying disease. Dyspnea occurs initially on exertion and later at rest. Dull chest pain resembling angina pectoris may be present. Fatigue and fainting on exertion occur as a result of reduced cardiac output related to elevated pulmonary artery pressures or bradycardia (slow heartbeat).
Laboratory findings include electrocardiographic changes of right axis deviation, right ventricular hypertrophy, right ventricular strain, or right arterial enlargement. Echocardiography is helpful in evaluating patients thought to have mitral stenosis and pulmonary valvular disease. Doppler ultrasonography is a reliable noninvasive means of estimating systolic pulmonary artery pressure. Depending upon the suspected cause of pulmonary hypertension, ventilation-perfusion lung scanning, pulmonary angiography, and open lung biopsy are occasionally helpful. Ventilation-perfusion lung scanning is very helpful in identifying patients with pulmonary hypertension caused by recurrent blood clots in the lungs. Transbronchial biopsy carries an increased risk of bleeding.
Conventional treatment of pulmonary hypertension includes oxygen therapy to decrease hypoxemia and resulting pulmonary vascular resistance. For patients with right ventricular failure, treatment also includes fluid restriction and diuretics to decrease intravascular volume and extravascular fluid accumulation. Most medications used to treat pulmonary hypertension are aimed at relaxing the blood vessels in the lungs and reducing excess cell growth. These include phosphodiesterase-5 inhibitors such as sildenafil (Revatio), prostanoids such as epoprostenol (Flolan), endothelin receptor antagonists such as bosentan (Tracleer), and calcium channel blockers such as diltiazem (Cardizem). An important goal of treatment is correction of the underlying cause.
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