Russell J. Miller, Gregory Matwiyoff, and John Scott Parrish

The evaluation and management of obstructive airways disease is the most common out-patient issue faced by pulmonologists. The initial evaluation requires a thorough and focused history and physical examination. Disease processes that cause airflow obstruction increase airways resistance since the flow of air is proportional to the change in pressure divided by the resistance (i.e., Ohm’s law). Airway resistance can be increased by a variety of mechanisms such as retained material within the airways (e.g., localized foreign body, secretions, mucous plugs, endobronchial tumors), hypertrophy of airway walls (e.g., chronic inflammation, edema, or smooth muscle hypertrophy), external compression (e.g., malignancy, vascular sling, goiter), and loss of radial traction (e.g., emphysema). Table 33-1 lists the locations and mechanisms of the more common types of airway obstruction.

Although asthma and chronic obstructive pulmonary disease (COPD) are the most common causes of airflow obstruction, many other conditions beginning in the mouth and affecting passage of air to the small airways (bronchioles 2 mm or less) may produce similar and sometimes confusing presentations. Typically, asthma is characterized by intermittent wheezing, chest tightness, and shortness of breath. In contrast, COPD typically presents with progressive chronic dyspnea, cough, and sputum production. Pulmonary specialists often are consulted by primary care providers to evaluate patients labeled with COPD or asthma who are unresponsive to traditional therapy. Although a lack of response may be due to suboptimal treatment, the patient’s status may be due to incorrect diagnosis or unrecognized concomitant problems.

Spirometry should be the initial step in the evaluation of possible obstructive airways disease. A disproportionate reduction of FEV₁ as compared to FVC is characteristic of obstruction. Although “office spirometry” is increasingly popular, poorly performed spirometry may be deceptive and lead to over or under diagnosis of obstructive disease. For example, if exhalation is not performed vigorously, FEV₁ and FVC both appear diminished prompting misleading conclusions. It is crucial that patient demographics and clinical parameters are accurately accounted for when population based “normals” are used as a comparison. Spirometry of questionable quality or with clinically incongruous results should be repeated in a setting with properly trained technicians. The numerical values obtained with spirometry also may be misleading and a thorough visual review of flow-volume curves also is important in separating large from small airway obstruction. There are three classical appearances of a flow-volume loop that may alert clinicians to the presence of large airway obstruction and its probable location: (1) fixed obstruction, (2) variable extrathoracic obstruction, and (3) variable intrathoracic obstruction.

FIXED OBSTRUCTION

A truncation of both the inspiratory and expiratory limbs of the flow-volume loop should raise the suspicion of central airway occlusion. This can occur secondary to a variety of malignant and nonmalignant disorders causing either extrinsic or intrinsic narrowing of the central airway. Many patients with central airway obstruction from tumors or foreign bodies present acutely with obvious symptoms of impending respiratory failure. However, patients with slowly progressive disease may present with more insidious symptoms that can be misinterpreted as asthma or COPD unresponsive to treatment. In the absence of other associated pulmonary or cardiac pathology, dyspnea may be a late finding in these patients. In an adult, exertional symptoms typically indicate a tracheal diameter of less than 8 mm and rest dyspnea indicates a diameter of less than 5 mm. The suspicion for central airway obstruction may be raised if the history discloses a previous malignancy (which may recur in the central airway), prolonged mechanical ventilation (which may damage the tracheal wall), or inflammatory collagen vascular diseases (which may result in airway scarring). Although physical exam findings may be nonspecific, the presence of stridor, or unilateral wheezing, should always be taken seriously and prompt further investigation. In patients with evidence of obstruction, the absence of findings related to the small airways (prolonged exhalation, enhancement of wheezes during end exhalation, etc.) may also raise the suspicion for central airway obstruction.

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