Pulmonary hypertension occurs when pulmonary artery pressure (PAP) rises above normal and isn’t attributable to the effects of aging or altitude. There isn’t a definitive set of values used to diagnose pulmonary hypertension; however, the National Institutes of Health requires that the resting mean PAP measures 25 mm Hg or more.
Primary, or idiopathic, pulmonary hypertension is rare, occurring most commonly in women between ages 20 and 40; pregnant women have the highest mortality. Secondary pulmonary hypertension results from existing cardiac or pulmonary disease. The prognosis depends on the severity of the underlying disorder.
Primary pulmonary hypertension begins as hypertrophy of the small pulmonary arteries. The medial and intimal muscle layers of these vessels thicken, decreasing distensibility and increasing resistance. This disorder then progresses to vascular sclerosis and obliteration of small vessels. Because this form of pulmonary hypertension occurs in association with collagen diseases, it’s thought to result from altered immune mechanisms.
Usually, pulmonary hypertension is secondary to hypoxemia from an underlying disease process, including:
alveolar hypoventilation from chronic obstructive pulmonary disease (most common cause in the United States), sarcoidosis, diffuse interstitial pneumonia, pulmonary metastasis, and certain diseases such as sclero-derma.
These diseases may cause pulmo-nary hypertension through alveolar destruction and increased pulmonary vascular resistance. Other disorders that cause alveolar hypoventilation without lung tissue damage include obesity, kyphoscoliosis, and obstructive sleep apnea.
vascular obstruction from pulmonary embolism, vasculitis, and disorders that cause obstructions of small or large pulmonary veins, such as left atrial myxoma, idiopathic veno-occlusive disease, fibrosing mediastinitis, and mediastinal neoplasm.
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