Total work of breathing plotted against respiratory rate forms a U-shaped curve, with elastic work falling and resistive work rising as rate changes. In a normal adult at rest, total work of breathing is minimal at a respiratory rate of approximately:

• A 35 breaths per minute
• B 25 breaths per minute
• C 15 breaths per minute ✓
• D 6 breaths per minute

Explanation

Slow, deep breathing favors large elastic work from stretching lungs and chest wall, while rapid, shallow breathing favors large resistive work from moving air quickly. The two curves sum to a U shape whose minimum in healthy adults lies near 15 breaths per minute, matching the usual resting rate. In restrictive disease with stiff lungs the optimum shifts toward faster rates, and in obstructive disease toward slower rates.

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

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