Chapter 4

Robert A. Winn, MD, & Edward D. Chan, MD

### Essentials of Diagnosis

• • In most instances spirometry is adequate to diagnose the presence of lung disease, although a specific diagnosis cannot be made with spirometry alone; patient history is needed.
• • Categorization of the physiology of lung disease into either obstructive or restrictive allows development of a differential diagnosis.
• • Lung volumes and diffusion refine the diagnosis.
• • Testing of muscle strength and bronchial provocation aid in difficult cases.

### General Considerations

Pulmonary function tests (PFTs) evaluate airflow obstruction, bronchodilator response, lung volumes, and gas exchange (diffusion capacity). Indications for pulmonary function testing are broad and include (1) evaluation of pulmonary symptoms to detect impairment and assess its severity, (2) classification of obstructive, restrictive, or mixed patterns of disease, (3) evaluation of response to various treatments including bronchodilators for asthma and corticosteroids for interstitial lung disease, and (4) monitoring pulmonary side effects of treatment (eg, methotrexate, amiodarone). Less commonly, PFTs are used for evaluation of disability in symptomatic patients and for preoperative evaluation. The latter includes operative risk for general surgery, transplant risk of postoperative pulmonary complications, and evaluation of the postoperative function for patients scheduled to undergo lung resection. Pulmonary function testing can also help define disease prognosis, eg, forced expiratory volume in 1 s (FEV1) has a relatively high correlation with the presence of chronic obstructive pulmonary disease (COPD), lung cancer, coronary artery disease, and stroke. For persons with occupational exposures, serial tracking may determine onset of disease and need for removal from the exposure. Many conditions causing obstructive or restrictive lung disease will be discussed in this chapter. Treatments for these numerous conditions are discussed in the respective disease-focused chapters in this volume.

It is important to understand that PFT values vary in healthy people. Unlike other tests that have a narrow normal range (eg, electrolytes, arterial blood gas, cholesterol panel), PFTs have a wide range of normal. In fact, the results obtained from PFTs are greatly influenced by the individual’s height, weight, age (few normal values have been generated for those less than 20 or greater than 70 years of age), sex (some normal values are based on males only), and race (predicted values for Hispanic, African-American, and Asian ethnicity are often 10–15% lower than for whites). It is clear that spirometry is highly effort dependent. Therefore, obtaining accurate measurements depends on cooperation and maximum patient effort, correctly calibrated equipment, and the use of trained respiratory personnel to conduct all tests. Furthermore, when interpreting the results of PFTs, it is imperative to consider the clinical context in which the test was ordered.

It is appropriate to order the components of PFTs (airflow/spirometry, lung volumes, diffusion capacity) based on specific symptoms and physical examination of the patient. Simple spirometry measures airflow, whereas full PFTs include, in addition to the spirometry, the measurement ...

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