A 48-year-old woman with progressive dyspnea has HRCT-proven idiopathic pulmonary fibrosis. At rest her respiratory rate is 32/min with tidal volume 280 mL, and she becomes distressed if asked to breathe slowly and deeply. Which principle of the work of breathing best explains her ventilatory pattern?

• A Total work of breathing is independent of tidal volume in restrictive disease
• B Flow-resistive work predominates in fibrosis and is minimized by rapid breathing
• C Elastic work predominates in fibrosis and is minimized by small tidal volumes ✓
• D Rapid shallow breathing maximizes alveolar ventilation per unit work

Explanation

In pulmonary fibrosis, stiff lungs raise elastic work, which rises steeply with tidal volume. Patients minimize total work by taking small tidal volumes at higher rates, since flow-resistive work, which favors slow deep breathing, is comparatively minor. Option B describes obstructive disease such as emphysema or asthma, where patients breathe slowly and deeply. Rapid shallow breathing actually lowers alveolar ventilation by increasing the wasted fraction spent on dead space.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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