Health Human Disease Blog

The normal pulmonary vasculature provides very low resistance to blood flow. However, when pulmonary hypertension occurs, right ventricular hypertrophy, dilation, and failure may develop. Pulmonary arterial hypertension results when there is increased flow in the pulmonary vascu­lature, when elevated pulmonary venous pressure is reflected back to the pulmonary arteries, or when the caliber of the pulmonary vasculature is decreased by either vasospasm or physical de­struction. Pulmonary heart disease (cor pulmon­ale) occurs when pulmonary arterial pressure is elevated secondary to dysfunction of the lungs and its vasculature and produces right heart fail­ure.

In primary pulmonary hypertension, intimal thickening of the pulmonary arteries and arter­ioles occurs with a characteristic “onion skin” vascular lesion. It occurs more frequently in women than in men. The pulmonary vascular re­sistance and pulmonary arterial pressure become markedly elevated. Left atrial and pulmonary cap­illary wedge pressures are normal, but right ven­tricular and right atrial pressures increase. The cardiac output may be normal or low, and the heart is unable to increase cardiac output with exercise. Functional tricuspid regurgitation may occur. Most patients become symptomatic late in the course of the disease. Fatigue and weakness are universal. Because of the low, fixed cardiac output, exertional syncope may result, which is an ominous sign; these patients may experience sudden cardiac death.

Secondary pulmonary hypertension can result from several etiologies. Pulmonary venous hy­pertension secondary to mitral stenosis often re­sults in a “reactive” pulmonary arterial vasocon­striction, increasing pulmonary vascular resis­tance and causing pulmonary hypertension. The cause of this reactive pulmonary hypertension is unclear, but upon relief of the mitral stenosis and decline of the pulmonary venous pressure, it usu­ally disappears. Various forms of congenital heart disease can result in pulmonary arterial hyper­tension, and many (for example, ventricular sep­tal defect) are not reversible once present. Pul­monary parenchymal diseases such as chronic obstructive pulmonary disease, restrictive lung disease, pneumoconiosis, and sarcoidosis can lead to pulmonary heart disease. Pulmonary vas­cular diseases such as recurrent pulmonary em­bolism and scleroderma can result in pulmonary hypertension. In addition, patients with disorders of their chest wall and muscles of respiration that lead to hypoventilation, such as kyphoscoliosis or sleep apnea syndrome, can develop right heart failure.

Acute pulmonary edema can occur in appar­ently normal patients exposed to the hypoxia of high altitudes. The precise mechanism is unclear, but these patients tend to have an exaggerated va­soconstrictive response of the pulmonary arter­ioles to hypoxia. This syndrome responds very quickly to oxygen administration.

Chronic obstructive pulmonary disease (COPD) is the most common cause of pulmonary heart dis­ease. Improvement of oxygenation is the best ther­apy for right heart failure associated with chronic lung disease. Aggressive treatment of the primary lung disorder with correction of hypoxia and aci­dosis decreases pulmonary vasoconstriction, and pulmonary hypertension improves.
Patients with pulmonary embolism may present with either dyspnea at rest, manifestations of pul­monary infarction including pleuritic pain, cough, and hemoptysis, circulatory collapse from massive pulmonary embolism, or unexplained ex­acerbation of known chronic heart failure. Large pulmonary emboli acutely elevate pulmonary ar­terial pressure and precipitate acute right heart failure.