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INTRODUCTION AND EPIDEMIOLOGY

The pulmonary vascular system is normally a high-flow, low-resistance circuit, with a mean pulmonary arterial pressure that constitutes approximately 15% to 20% of the systemic circulation.1 Normal pulmonary arterial systolic pressures range from 15 to 30 mm Hg, and diastolic pulmonary arterial pressures range from 4 to 12 mm Hg.1 Pulmonary hypertension exists when a mean pulmonary arterial pressure is >25 mm Hg at rest or >30 mm Hg during exertion.1,2

Pulmonary hypertension classification uses measurements of pulmonary arterial pressure, pulmonary vascular resistance, and pulmonary capillary wedge pressure (Table 58-1).1,3 Although echocardiography estimates pulmonary arterial pressure in a patient with suspected pulmonary hypertension, definitive diagnosis requires right heart catheterization.

TABLE 58-1World Health Organization Classification of Pulmonary Hypertension

Patients with group 1 pulmonary arterial hypertension have a mean pulmonary arterial pressure >25 mm Hg, a pulmonary vascular resistance >240 dynes/s/cm5, and a pulmonary capillary wedge pressure <15 mm Hg.2 Group 2 disease is caused by left heart disease and is the most common etiology.2 Group 3 occurs with chronic hypoxemic lung disease. Chronic thromboembolic pulmonary hypertension, group 4, develops in up to 4% of patients with thromboembolic disease.4-6 Regardless of the cause, pulmonary hypertension is associated with high rates of morbidity and mortality,4,7 with a 5-year death rate for patients with idiopathic pulmonary arterial hypertension exceeding 30%.8

PATHOPHYSIOLOGY

Pulmonary arterial hypertension consists of vascular remodeling in all layers of small and mid-sized pulmonary arterioles, plus inflammation and in situ thrombosis formation.9 Additional pathology includes alterations in microvascular permeability, hypoxic vasoconstriction, and plexiform lesion formation in arteriolar walls. The cumulative effect of these changes is sustained elevations of pulmonary vascular resistance and impaired pulmonary blood flow.

With persistent elevations in pulmonary vascular resistance, the right ventricle (RV) dilates. RV dilation leads to increased ventricular wall tension during systole, increased oxygen consumption, and eventually decreased contractility. With progressive RV dilation, the intraventricular septum displaces toward the left ventricle, which inhibits left ventricular filling and ultimately impairs cardiac output ...

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