Robert A. Winn, MD, & Edward D. Chan, MD
- • 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
- • Lung volumes and diffusion refine the diagnosis.
- • Testing of muscle strength and bronchial provocation
aid in difficult cases.
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 ...