What term describes the ease with which the lungs expand and accept a gas?

• A. Elastance
• B. Capacitance
• C. Resistance
• D. Compliance

Answer: (D)

The ease with which the lungs expand and accept a gas is described by compliance. It measures how easily the lungs (and chest wall) stretch as pressure rises, so a small pressure change yields a relatively large volume change when compliance is high. Conversely, low compliance means the lungs are stiff and require a larger pressure change to achieve the same volume. Compliance is defined as ΔV/ΔP (volume change per unit pressure change) and is typically expressed in mL per cm H2O. This concept is the opposite of elastance, which describes how strongly the lungs recoil; higher elastance means stiffer lungs. Resistance concerns how hard it is for air to flow through the airways, not how the lungs inflate.