The amount of pressure required to inflate the lungs is dependent on which factors?

• A. Static compliance and airway resistance
• B. Dynamic compliance and airway resistance
• C. Lung volumes and airway resistance
• D. Static compliance and PEEP

Answer: (A)

Inflating the lungs mainly comes down to two opposing forces: elastic recoil and airway resistance. The elastic recoil of the lung and chest wall acts like a spring—the stiffer the system (lower static compliance), the more pressure you must generate to achieve a given volume. Static compliance isolates this elastic property when there’s no gas flow, so it is the best measure of how much pressure is needed to overcome the lung/chest wall elasticity. As air moves in, it also encounters resistance in the airways, which creates an additional pressure drop that you must overcome to drive the flow. So the pressure required to inflate the lungs reflects both static compliance (elastic load) and airway resistance (resistive load). Lung volumes and baseline pressures like PEEP influence overall pressures but don’t set the core relationship as directly as these two factors.