Porth's Essentials of Pathophysiology, 4e

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Respiratory Function

U N I T 6

respiratory symptoms (shortness of breath, nonpro- ductive cough, chest pain) or constitutional signs and symptoms (e.g., fever, sweating, anorexia, weight loss, fatigue, myalgia). Eye involvement (anterior uveitis) and skin involvement (skin papules and plaques) are partic- ularly common extrathoracic manifestations, but there may be cardiac, neuromuscular, hematologic, hepatic, endocrine, and lymph node findings. Sarcoidosis is characterized by either progressive chronicity or periods of activity interspersed with remis- sions, sometimes permanent, that may be spontaneous or induced by corticosteroid therapy. Approximately 65% to 75% of persons recover with minimal clinical and radiographic abnormalities. 15 Other persons have persistent radiographic abnormalities and progression of their respiratory symptoms, with or without addi- tional extrathoracic disease. The diagnosis of sarcoidosis is based on history and physical examination, tests to exclude other diseases, chest radiography, and biopsy to obtain confirmation of noncaseating granulomas. A thorough ophthalmologic evaluation is recommended for most persons, even those without ocular symptoms. Treatment is directed at interrupting the granuloma- tous inflammatory process that is characteristic of the disease and managing the associated complications. When treatment is indicated, corticosteroid drugs are used. These agents produce clearing of the lung, as seen on the chest radiograph, and improve pulmonary func- tion, but it is not known whether they affect the long- term outcome of the disease. ■■ The interstitial lung diseases are a diverse group of lung disorders that produce similar inflammatory and fibrotic changes in the interstitium or alveolar septa of the lung. As a result, the lungs become stiff and difficult to inflate, increasing the work of breathing and causing dyspnea and decreased exercise tolerance due to hypoxemia, without evidence of wheezing or signs of airway obstruction. ■■ These diseases include drug- and radiation- induced lung disease, environmental and occupational lung diseases caused by inhalation of organic and inorganic dusts, immunologic lung disorders such as those that accompany scleroderma, idiopathic pulmonary fibrosis, and sarcoidosis. ■■ The restrictive lung disorders reduce the diffusing capacity of the lung, producing various degrees of hypoxemia, dyspnea, tachypnea, and eventual cyanosis. SUMMARY CONCEPTS

Disorders of the Pulmonary Circulation As blood moves through the pulmonary capillaries, the oxygen content increases and the carbon dioxide decreases. These processes depend on the matching of ventilation (i.e., gas exchange) and perfusion (i.e., blood flow). This section discusses two major prob- lems of the pulmonary circulation: pulmonary embo- lism and pulmonary hypertension. Pulmonary edema, another major problem of the pulmonary circulation, is discussed in Chapter 20. Pulmonary Embolism Pulmonary embolism develops when a blood-borne substance lodges in a branch of the pulmonary artery and obstructs blood flow. 15,16,59,61 The embolism may consist of a thrombus (Fig. 23-13), air that has acci- dentally been injected during intravenous infusion, fat that has been mobilized from the bone marrow after a fracture or from a traumatized fat depot, or amniotic fluid that has entered the maternal circulation during childbirth.

FIGURE 23-13. Pulmonary embolism. The main pulmonary artery and its bifurcation have been opened to reveal a large saddle embolus. (From McManus BM, Allard MF, Yanagawa R. Hemodynamic disorders. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2012:275. Courtesy of Dr. Greg J. Davis.)