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The lung brings the ambient air that we breathe into close proximity with the systemic circulation. This allows for its essential function in gas exchange. However, this also exposes the lung to a variety of potentially injurious infectious and noninfectious environmental agents. The normal host response to such insults is to eradicate the etiologic agent and to repair the injury caused either directly by the agent or indirectly by the associated inflammatory process. This complex but well orchestrated and tightly regulated host response leads to eventual resolution of injury and restoration of normal lung architecture and function in most cases. However, if the inflammatory and/or repair response is dysregulated, a chronic alveolar/interstitial remodeling process with varying degrees of inflammation and fibrosis ensues. Damage to the pulmonary vascular endothelium via the circulation (e.g., drugs, systemic rheumatic disorders) may produce similar inflammatory/fibrotic reactions in the lung. This results in the restrictive physiology and gas-exchange abnormalities characteristic of the diffuse parenchymal lung diseases (DPLDs). When all potential etiologic agents and associations are considered, the list of DPLDs includes over 150 different clinical entities (Table 84-1). Thus, DPLDs comprise a large and heterogeneous group of diseases that are grouped into a single category based on common features in their clinical, radiographic, and physiological presentations.

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Table 84-1 Classification of Diffuse Parenchymal Lung Disease (DPLD)
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The most prevalent and devastating of all the DPLDs is idiopathic pulmonary fibrosis (IPF), a chronic fibrotic disease of unknown etiology. IPF is primarily a disease of elderly patients. Elderly patients maybe particularly susceptible to this disease because of inherent deficiencies in immune function and/or in their inability to mount an appropriate repair response. Alternatively, IPF may present in elderly patients as a result of accumulated ...

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