Intrinsic work of breathing (WOB) is defined as the energy required to do what?

• A. Energy required to move blood through the circulatory system
• B. Energy required to ventilate the alveoli
• C. Energy required to move gas through the airways and expand the thorax
• D. Energy required to overcome chest wall resistance only

Answer: (C)

Intrinsic work of breathing is the energy the respiratory muscles must provide to ventilate the lungs. This specifically means the energy needed to move air through the airways and to expand the thorax and lungs against their elastic recoil. In other words, it encompasses both airway resistance and the elastic forces of the lungs and chest wall that must be overcome during inspiration and expiration.

This is not the energy tied to moving blood through the circulatory system, which is a cardiovascular function, nor is it limited to just ventilating the alveoli in isolation. It also isn’t correct to think it means only overcoming chest wall resistance, because the lungs’ elastic recoil and airway resistance contribute to the total work. The best description, therefore, is the energy required to move gas through the airways and expand the thorax.