PFTs evaluate the ventilatory system and alveoli in an indirect, overlapping way. The patient’s age, height, weight, ethnicity, and gender are recorded before testing because they are the basis for calculating predicted or normal reference values.
PFTs are generally divided into three categories:
Airway flow rates typically include measurements of instantaneous or average airflow rates during a maximal forced exhalation to assess airway patency and resistance. These tests also assess responses to inhaled bronchodilators or bronchial provocations.
Lung volumes and capacities measure the various air-containing compartments of the lung to assess air trapping (hyperinflation, overdistention) or reduction in volume. These measurements also help to differentiate obstructive from restrictive ventilatory impairments.
Gas exchange (diffusion capacity or transfer factor) measures the rate of gas transfer across the alveolar capillary membranes to assess the diffusion process. It can also monitor for side effects of drugs, such as bleomycin (antineoplastic agent) or amiodarone (antiarrhythmic agent), which can cause interstitial pneumonitis or pulmonary fibrosis. Diffusion capacity in the absence of lung disease (e.g., anemia) can also be evaluated.