A 45-year-old woman with idiopathic pulmonary fibrosis breathes spontaneously at a rate of 28 per minute with a tidal volume of 250 mL. This rapid, shallow pattern is best explained by:

• A Loss of the Hering-Breuer inflation reflex
• B Increased dead space ventilation forcing larger tidal volumes
• C Stimulation of central chemoreceptors by retained carbon dioxide
• D Reduced elastic work of breathing achieved by lowering tidal volume ✓

Explanation

Total work of breathing has an elastic component, proportional to tidal volume, and a resistive component, proportional to airflow velocity. Fibrosis raises elastic recoil, so the minimum-work strategy shifts toward small tidal volumes at higher frequencies, minimising elastic work. The patient remains normocapnic or hypocapnic early on, so central chemoreceptor drive does not explain the pattern, killing option C.

Reference: West's Respiratory Physiology: The Essentials, 10th ed.

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