Chapter 251

The majority of diseases of the respiratory system fall into one of three major categories: (1) obstructive lung diseases; (2) restrictive disorders; and (3) abnormalities of the vasculature. Obstructive lung diseases are most common and primarily include disorders of the airways such as asthma, chronic obstructive pulmonary disease (COPD), bronchiectasis, and bronchiolitis. Diseases resulting in restrictive pathophysiology include parenchymal lung diseases, abnormalities of the chest wall and pleura, as well as neuromuscular disease. Disorders of the pulmonary vasculature are not always recognized and include pulmonary embolism, pulmonary hypertension, and pulmonary venoocclusive disease. Although many specific diseases fall into these major categories, both infective and neoplastic processes can affect the respiratory system and may result in myriad pathologic findings, including obstruction, restriction, and pulmonary vascular disease (see Table 251-1).

Table 251–1. Categories of Respiratory Disease

The majority of respiratory diseases present with abnormal gas exchange. Disorders can also be grouped into the categories of gas exchange abnormalities, including hypoxemic, hypercarbic, or combined impairment. Importantly, many diseases of the lung do not manifest gas exchange abnormalities.

As with the evaluation of most patients, the approach to a patient with disease of the respiratory system begins with a thorough history. A focused physical examination is helpful in further categorizing the specific pathophysiology. Many patients will subsequently undergo pulmonary function testing, chest imaging, blood and sputum analysis, a variety of serologic or microbiologic studies, and diagnostic procedures, such as bronchoscopy. This step-wise approach is discussed in detail below.

### Dyspnea and Cough

The cardinal symptoms of respiratory disease are dyspnea and cough (Chaps. 33 and 34). Dyspnea can result from many causes, some of which are not predominantly caused by lung pathology. The words a patient uses to describe breathlessness or shortness of breath can suggest certain etiologies of the dyspnea. Patients with obstructive lung disease often complain of “chest tightness” or “inability to get a deep breath,” whereas patients with congestive heart failure more commonly report “air hunger” or a sense of suffocation.

The tempo of onset and duration of a patient's dyspnea are helpful in determining the etiology. Acute shortness of breath is usually associated with sudden physiological changes, such as laryngeal edema, bronchospasm, myocardial infarction, pulmonary embolism, or pneumothorax. Patients with underlying lung disease commonly have progressive shortness of breath or episodic dyspnea. Patients with COPD and idiopathic pulmonary fibrosis ...

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