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INTRODUCTION

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Diseases of the respiratory system are an important public health problem in all countries. The respiratory system, which includes the lungs and the upper airway that joins the trachea to the larynx, is exposed to a wide range of potentially injurious agents (Table 65-1). On average, an adult inhales about 5 L of air per minute; with exercise, the amount may increase 20-fold or more. With 10,000–20,000 L of air inhaled daily, agents present even in low concentrations may be toxic. The respiratory system is equipped with a remarkably effective system of defense mechanisms against inhaled particles and gases. Disease may result, however, if an acute exposure overwhelms the defenses (e.g., toxic gas inhalation), if an agent is particularly toxic even at low concentrations (e.g., toluene diisocyanate), if exposure is sustained (e.g., cigarette smoking), or if the exposed person is particularly susceptible (e.g., asthmatics).

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TABLE 65-1MECHANISMS OF LUNG INJURY AND EXAMPLES OF INJURIOUS AGENTS AND ASSOCIATED DISEASES
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Respiratory diseases are major causes of disability and death worldwide,1,2 with over 11 million deaths or about 20% of all deaths due to perinatal respiratory conditions, lower respiratory tract infections, chronic respiratory diseases, and lung cancer (Table 65-2). The distributions of causes-of-death from respiratory diseases varies between countries and regions with lower respiratory tract infections predominating in the developing countries of Africa, Eastern Mediterranean, and Southeast Asia; and chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma, and lung cancer deaths occurring more frequently in more developed regions including the Americas, Europe, and Western Pacific. Among children under 5 years of age, about 21% of all deaths, or 2.27 million deaths in 2000, were due to pneumonia;3 and about 90% of these deaths were among children from 42 developing countries. The markedly higher childhood mortality from acute respiratory tract infections in developing countries as compared with those in developed countries probably reflects poorer nutrition and immunization practices and more frequent low birth weight, crowding, and indoor and outdoor air pollution.4 Emerging infections (e.g., SARS) and increasing international travel are a growing public health concern for children and adults.5

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TABLE 65-2WORLDWIDE AND REGIONAL NUMBERS OF DEATHS(×1000) FROM RESPIRATORY DISEASES, 2002

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