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NORMAL FUNCTIONS OF THE PERICARDIUM
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The normal pericardium is a double-layered sac; the visceral pericardium is a serous membrane that is separated from the fibrous parietal pericardium by a small quantity (15–50 mL) of fluid, an ultrafiltrate of plasma. The normal pericardium, by exerting a restraining force, prevents sudden dilation of the cardiac chambers, especially the right atrium and ventricle, during exercise and with hypervolemia. It also restricts the anatomic position of the heart, and probably retards the spread of infections from the lungs and pleural cavities to the heart. Nevertheless, total absence of the pericardium, either congenital or after surgery, does not produce obvious clinical disease. In partial left pericardial defects, the main pulmonary artery and left atrium may bulge through the defect; very rarely, herniation and subsequent strangulation of the left atrium may cause sudden death.
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Acute pericarditis, by far the most common pathologic process involving the pericardium (Table 265-1), has four principal diagnostic features:
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Chest pain is usually present in acute infectious pericarditis and in many of the forms presumed to be related to hypersensitivity, autoimmunity, or of unknown cause (idiopathic). The pain of acute pericarditis is often severe, retrosternal and/or left precordial, and referred to the neck, arms, or left shoulder. Frequently the pain is pleuritic, consequent to accompanying pleural inflammation (i.e., sharp and aggravated by inspiration and coughing), but sometimes it is steady, radiates to the trapezius ridge, or into either arm, and resembles that of myocardial ischemia; therefore, confusion with acute myocardial infarction (AMI) is common. Characteristically, pericardial pain may be intensified by lying supine, and relieved by sitting up and leaning forward (Chap. 11). ...