Which expression correctly defines work of breathing in this context?

• A. Tidal volume X Frequency
• B. Pressure (force) X Volume (displacement)
• C. Change in pressure/Change in flow
• D. Power X Time

Answer: (B)

Work of breathing represents the energy muscles spend to move air into and out of the lungs, overcoming elastic recoil and airway resistance. For a breath, the energy required is the pressure the muscles must generate times the amount of air moved—the tidal volume. In physics terms, work is the integral of pressure with respect to volume, W = ∫ P dV, and a practical approximation is ΔP × ΔV. Therefore, pressure (force) × volume (displacement) best defines work of breathing in this context. The other expressions describe different concepts: tidal volume × frequency gives minute ventilation, a flow-resistance relationship isn’t the direct work, and power × time would give total energy over a period, not the per-breath work.