Porth's Essentials of Pathophysiology, 4e

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Respiratory Function

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available for replacement therapy in persons with a hereditary deficiency of the enzyme. There are two commonly recognized types of emphy- sema: centriacinar or centrilobular, and panacinar (Fig. 23-9). The centriacinar type affects the bronchioles in the central part of the respiratory lobule, with initial preservation of the alveolar ducts and sacs. 16 It is the most common type of emphysema and is seen predomi- nantly in male smokers. The panacinar type produces initial involvement of the peripheral alveoli and later extends to involve the more central bronchioles. This type of emphysema is more common in persons with α 1 -antitrypsin deficiency. It also is found in smokers in association with centriacinar emphysema. Chronic Bronchitis Chronic bronchitis represents airway obstruction of the major and small airways. 15,16 The condition is seen most commonly in middle-aged men and is associated with chronic irritation from smoking and recurrent infec- tions. A clinical diagnosis of chronic bronchitis requires a history of a chronic productive cough that has per- sisted for at least 3 consecutive months in at least 2 con- secutive years. 44 Typically, the cough has been present for many years, with a gradual increase in acute exacer- bations that produce frankly purulent sputum. The earliest feature of chronic bronchitis is hyperse- cretion of mucus in the large airways, associated with hypertrophy of the submucosal glands in the trachea and bronchi. 15,16 Although mucus hypersecretion in the large airways is the cause of sputum overproduction, the accompanying changes in the small airways (small bron- chi and bronchioles) are now thought to be important in the airway obstruction that develops. 15 Histologically, these changes include a marked increase in goblet cells and excess mucus production with plugging of the air- way lumen, inflammatory infiltration, and fibrosis of the bronchiolar wall. It is thought that both the submuco- sal hypertrophy in the larger airways and the increase in goblet cells in the smaller airways are a protective reaction against tobacco smoke and other pollutants. Viral and bacterial infections are common in persons with chronic bronchitis and are thought to be a result rather than a cause of the disease. While infections are not responsible for initiating the disease process, they are probably important in maintaining it and may be critical in producing acute exacerbations. Manifestations The clinical manifestations of COPD usually have an insidious onset and persons characteristically seek medical attention in the fifth or sixth decade of life, with manifestations of excessive cough, sputum pro- duction, and shortness of breath. 10,44 The productive cough usually occurs in the morning and the dys- pnea becomes more severe as the disease progresses. Frequent exacerbations of infection and respiratory insufficiency are common, causing absence from work and eventual disability. The late stages of COPD are characterized by recurrent respiratory infections and

Terminal bronchiole

Respiratory bronchiole

Alveoli

Normal

Terminal bronchiole

Respiratory bronchiole

Alveoli

Centriacinar

Terminal bronchiole

Respiratory bronchiole

Alveoli

Panacinar

chronic respiratory failure. Death usually occurs dur- ing an exacerbation of illness associated with infection and respiratory failure. The mnemonics “pink puffer” and “blue bloater” have been used to differentiate the clinical manifes- tations of emphysema and chronic obstructive bron- chitis. 15 Persons with predominant emphysema are classically referred to as pink puffers, a reference to the lack of cyanosis, the use of accessory muscles, and pursed-lip (“puffer”) breathing. With loss of lung elasticity and hyperinflation of the lungs, the airways often collapse during expiration because pressure in surrounding lung tissues exceeds airway pressure. Air becomes trapped in the alveoli and lungs, producing an increase in the anteroposterior dimensions of the chest, the so-called barrel chest that is typical of persons with emphysema (Fig. 23-10). Such persons have a dra- matic decrease in breath sounds throughout the chest. Because the diaphragm may be functioning near its maximum ability, the person is vulnerable to diaphrag- matic fatigue and acute respiratory failure. Persons with a clinical syndrome of chronic bronchitis are classically FIGURE 23-9. Centriacinar and panacinar emphysema. In centriacinar emphysema, the destruction is confined to the terminal (TB) and respiratory bronchioles (RB). In panacinar emphysema, the peripheral alveoli (A) are also involved. (Adapted fromWest JB. Pulmonary Pathophysiology:The Essentials. 7th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2008:56.)