Definition
Sustained elevation of mean pulmonary arterial pressure.

Pathogenesis
Elevated pressure, through endothelial cell dysfunction, produces structural changes in the pulmonary vasculature. These changes ultimately decrease pulmonary blood flow and stress the heart to the point of failure. Based on etiology, pulmonary hypertension is divided into two categories.

• Primary (idiopathic): The cause is unknown.
• Secondary: The hypertension is secondary to a variety of conditions which increase pulmonary blood flow or increase resistance to blood flow. Example: Interstitial fibrosis.

Pathology
The changes involve large and small pulmonary blood vessels and range from mild to severe. The major changes include atherosclerosis, striking medial hypertrophy and intimal fibrosis of small arteries and arterioles, and plexogenic arteriopathy. Refer to Figure 15-7 in your textbook.

Pathophysiology
Dyspnea and fatigue eventually give way to irreversible respiratory insufficiency, cyanosis and cor pulmonale.