Why is spirometry often challenging to perform in children under five years of age?

• A. They are unable to sit still for the test.
• B. They cannot understand the instructions without reading.
• C. They have low lung volumes that preclude measurement.
• D. Younger children have difficulty following instructions and producing reliable expiratory effort.

Answer: (D)

Spirometry hinges on the patient performing a rapid, maximal exhalation after a full inhalation, with good cooperation and a proper mouth seal. In children under five, there’s often limited ability to understand and follow the maneuvers, plus developing breath control and coordination. This leads to inconsistent effort, early termination of the blow, leaks around the mouthpiece, and variable results, making it hard to obtain reliable, acceptable measurements. The main barrier isn't simply sitting still, reading instructions, or having low lung volumes—the core issue is the difficulty in generating a reliable, maximal expiratory effort due to developmental factors.