In cystic fibrosis, pulmonary function tests typically show what pattern?

• A. Decreased expiratory flow and increased FRC
• B. Increased expiratory flow and increased FRC
• C. Decreased inspiratory capacity
• D. Normal expiratory flow and normal FRC

Answer: (A)

Pulmonary function tests in cystic fibrosis show an obstructive pattern with air trapping. The thick mucus and bronchial inflammation narrow the small airways, especially during expiration, so expiratory flow is reduced (lower FEV1 and often a reduced FEV1/FVC ratio). Because not all the air can be exhaled, air remains in the lungs at the end of expiration, increasing the functional residual capacity. In many patients, total lung capacity and residual volume are also elevated due to this hyperinflation, and inspiratory capacity can be reduced as resting lung volumes rise.

So the hallmark is decreased expiratory flow from airway obstruction with increased end-expiratory lung volumes from air trapping. Choices suggesting increased expiratory flow, normal flow with normal volumes, or decreased inspiratory capacity alone don’t fit this obstructive, air-trapping pattern.