How is the work of breathing (WOB) calculated?

The work of breathing (WOB) is a critical concept in respiratory physiology, defined as the energy expended to overcome the resistance of the airways and the elastic recoil of the lungs during inspiration and expiration. To calculate the work of breathing, it is essential to relate the changes in pressure and volume that occur during respiration.

The correct formula for calculating WOB incorporates both the change in pressure and change in volume, which can be expressed as the product of the pressure change and volume change. Specifically, this reflects the fact that work is a function of force applied over distance—where pressure can be considered as the force per unit area exerted on the airways and volume as the distance over which that pressure acts within the lungs. Therefore, the work done during breathing is expressed as the change in pressure multiplied by the change in volume.

This understanding forms the basis for option C being the correct choice, as it accurately represents the interdependence of pressure and volume during the respiratory cycle and provides a means of quantifying the energy required for ventilation.