By contrast, in diffuse restrictive diseases, FVC is reduced and the expiratory flow rate is normal or reduced proportionately. Hence, the ratio of FEV to FVC is near normal. Restrictive defects occur in two general conditions: (1) chest wall disorders in the presence of normal lungs (e.g., with severe obesity, diseases of the pleura, and neuromuscular disorders, such as the Guillain-Barré syndrome [Chapter 22], that affect the respiratory muscles) and (2) acute or chronic interstitial lung diseases. The classic acute restrictive disease is ARDS, discussed earlier. Chronic restrictive diseases (discussed later) include the pneumoconioses, interstitial fibrosis of unknown etiology, and infiltrative conditions such as sarcoidosis.
In their prototypical forms, the four disorders in this group—emphysema, chronic bronchitis, asthma, and bronchiectasis—have distinct clinical and anatomic characteristics (
Table 13.1 ), but overlaps between emphysema, chronic bronchitis, and asthma are common.
It should be noted that emphysema is defined on the basis of morphologic and radiologic features, whereas chronic bronchitis is defined on the basis of clinical features (described later). The anatomic distribution of these disorders also is somewhat different, as chronic bronchitis initially involves the large airways, whereas emphysema affects the acinus. In severe or advanced cases of both, small airway disease (chronic bronchiolitis) is also present. Although emphysema may exist without chronic bronchitis (particularly in inherited α1-anti-trypsin deficiency, discussed later) and vice versa, the two diseases usually coexist. This is almost certainly because cigarette smoking is the major underlying cause of both. In view of their propensity to coexist, emphysema and chronic bronchitis often are grouped together under the rubric of chronic obstructive pulmonary disease (COPD). COPD affects more than 10% of the U.S. adult population and is the fourth leading cause of death in this country. The largely irreversible airflow obstruction of COPD distinguishes it from asthma, which, as discussed later, is characterized by reversible airflow obstruction (
Fig. 13.4
Emphysema is characterized by permanent enlargement of the air spaces distal to the terminal bronchioles, accompanied by destruction of their walls without significant fibrosis. It is classified according to its anatomic distribution. As discussed earlier, the acinus is the structure distal to terminal bronchioles, and a cluster of three to five acini is called a lobule (
Fig. 13.5A ). There are four major types of emphysema: (1) centriacinar, (2) panacinar, (3) distal acinar, and (4) irregular. Only the first two types cause significant airway obstruction, with centriacinar emphysema being about 20 times more common than panacinar disease.
• Centriacinar (centrilobular) emphysema. The distinctive feature of centriacinar emphysema is that the central or proximal parts of the acini, formed by respiratory http://ebooksmedicine.net
Table 13.1 Disorders Associated With Airflow Obstruction:The Spectrum of Chronic Obstructive Pulmonary Disease
ChronicbronchitisBronchusMucousglandhypertrophyandTobaccosmoke,airpollutantsCough,sputumproductionhyperplasia,hypersecretion
BronchiectasisBronchusAirwaydilationandscarringPersistentorsevereinfectionsCough,purulentsputum,fever
EmphysemaAcinusAirspaceenlargement,wallTobaccosmokeDyspneadestruction
Smallairwaydisease,BronchioleInflammatoryscarring,partialTobaccosmoke,airpollutantsCough,dyspneabronchiolitis *Canbepresentinallformsofobstructivelungdiseaseorbyitself.